Flood Resistant Bridge Design in PNG rev0117 draft

FLOOD RESISTANT BRIDGE DESIGN in Papua New Guinea

Solution to Flood affected Bridges Gibson Ali Holemba

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Flood Resistant Bridge Design in Papua New Guinea

Gibson Holemba

Title Page

Flood Resistant Bridge Design in Papua New Guinea by

Gibson Ali Holemba B Eng. (Civil), PE, MJSCE, MIEPNG, Civil Engineer

A research proposal submitted in partial fulfilment of the requirements for the

award of Master of Engineering Degree in Civil Engineering Division of Engineering and Policy for Sustainable Environment,

Graduate School of Engineering, Hokkaido University

January 2017

The author holds the copyright of this research proposal, and the content of this proposal is the opinion of the author. All materials and citations from borrowed sources are in the reference section.

Division of Engineering and Policy for Sustainable Environment Graduate School of Engineering

Hokkaido University

© 2017 Gibson Ali Holemba

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Abstract Papua New Guinea has been experiencing frequent bridge washouts and collapses due to flooding rivers in the last Five (5) years. According to the record from Department of Works – PNG has shown that over Two Hundred and Eighty (280) bridges, fords (causeways) and major culverts were damaged by flood action. The damage of bridges has been observed to be mainly at the bridge foundations. More specifically, the flooding waters basically wash away the abutments or scour the piers to weaken the load capacity and eventually destroy the bridge. In addition, it is also attested that bank and embankment erosion by flooding rivers and subsequent leading to the further damage of the bridge structure has been accepted widely in Papua New Guinea. Therefore, this study will undertake field studies on the flood-affected bridges in PNG and Japan and provide recommended flood resilient bridge design policies and guidelines for use in Papua New Guinea. The outcome of the research will take into account the constructability and technological issues in Papua New Guinea, which a more practical policy paper that is economical and sustainable for the growing economy of the nation is prepared for approval and implementation. All in all, the flood resistant improved design will pave the way forward to bridge design engineers, consultants and contractors to design and construct bridges that are flood resilient, providing more innovative, safe and reliable methods that are economically viable for bridges in PNG. This is a need and will make a big difference for the government and the road transport organisations that are spending beyond their budgetary allocations for emergency restoration works and construction of new bridges to provide service to the people. Key Words: Flood, Resistant, Bridge damage, Abutment, Pier, Embankment,

Scour, and Bank.

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Acknowledgement I wish to acknowledge the following people for their utmost contribution and support to this research paper:

To my Almighty God for his countless wisdom and knowledge. To my beautiful wife Melissa and the kids, Davis and Alissa. To my Supervisor Professor Takashi Matsumoto for his guidance

and advises in the successful completion of this research. Mr David Wereh, Secretary of Works & Implementation in approving my

study application Mr Steven Pup, Deputy Secretary (Operations) of Department of Works

in Papua New Guinea. Mr Andrew Kendaura, Provincial Works Manager – Department of

Works Provincial Office – Madang Province, PNG for the field data. JICA and AsiaSEED my Scholarship Program Managers and

Coordinators. The Government of Japan for the establishment and funding of the

Pacific Leaders’ Educational Assistance for the Development of States Scholarship Program (Pacific LEADS).

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Table of Contents

Title Page --------------------------------------------------------------------------------------- II

Abstract ---------------------------------------------------------------------------------------- III

Acknowledgement -------------------------------------------------------------------------- IV

List of Figures ------------------------------------------------------------------------------- VII

List of Tables ------------------------------------------------------------------------------- VIII

List of Equations -------------------------------------------------------------------------- VIII

Glossary of Terms -------------------------------------------------------------------------- X

Chapter 1.0 Introduction ----------------------------------------------------------------- 30 1.1 Background to Study --------------------------------------------------------------- 30 1.2 Problem Statement ----------------------------------------------------------------- 31 1.3 Purpose of the Research --------------------------------------------------------- 31 1.4 Scope of the Research ------------------------------------------------------------ 32 1.5 Hypothesis ---------------------------------------------------------------------------- 32 1.6 Importance of Study ---------------------------------------------------------------- 32 1.7 Study Limitations -------------------------------------------------------------------- 34 1.8 Preview of this Study -------------------------------------------------------------- 34

Chapter 2.0 Theory and Literature Review ---------------------------------------- 35 2.1 Introduction ------------------------------------------------------------------------------- 35 2.2 Flood --------------------------------------------------------------------------------------- 35 2.3 History of Bridge Damaged by Flood ---------------------------------------------- 37 2.4 Bridge Abutment Design -------------------------------------------------------------- 39

2.4.1 Types of Abutments -------------------------------------------------------------- 40 2.4.2 Constriction Flow at Bridge Abutments -------------------------------------- 41 2.4.3 Bridge Abutment on Flood Plain ---------------------------------------------- 44

2.5 Bridge Pier Design --------------------------------------------------------------------- 45 2.5.1 Methods for Estimating Scour at Bridge Piers ----------------------------- 46 2.5.2 General Scour ---------------------------------------------------------------------- 46 2.5.3 Local Scour ------------------------------------------------------------------------- 48 2.5.4 Combined Scour ------------------------------------------------------------------- 50 2.5.5 Hydrodynamic Flow Pressure on Bridge Piers ---------------------------- 50 2.5.6 Drag and Lift Forces on Bridge Pier ------------------------------------------ 51

2.6 Bridge Foundation Design ------------------------------------------------------------ 54 2.6.1 Hydrostatic Earth Pressures on Bridge Foundations -------------------- 55 2.6.2 Methods for Estimating Active (Pa) and Passive (Pp) Earth Pressure Forces --------------------------------------------------------------------------------------- 60

2.7 Design of Flow ----------------------------------------------------------------------- 71 2.7.1 Introduction ------------------------------------------------------------------------ 71 2.7.2 Flood Design and Estimation ------------------------------------------------- 72 2.7.3 Regional Flood Frequency Method ----------------------------------------- 73 2.7.4 Rational Method ------------------------------------------------------------------ 76 2.7.5 Estimation of Large and Extreme Floods ---------------------------------- 77

2.8 Design for Structural Stability ---------------------------------------------------- 78 2.8.1 Design for Structural Adequacy ---------------------------------------------- 78 2.8.2 Design for Foundation Adequacy-------------------------------------------- 78 2.8.3 Design for Flood Protection Structures ------------------------------------ 79

2.9 Design of Afflux in Bridges ------------------------------------------------------- 79

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2.9.1 What is Afflux? ------------------------------------------------------------------- 79 2.9.2 Importance of Afflux in Bridge Design -------------------------------------- 80 2.9.3 Afflux Estimation Methods ----------------------------------------------------- 80 2.9.4 Afflux at Arch Bridges----------------------------------------------------------- 81

2.10 Bridge Scour and Countermeasures --------------------------------------------- 83 2.10.1 Introduction --------------------------------------------------------------------- 83 2.10.2 Countermeasure Planning and Design --------------------------------- 83 2.10.3 Bridge Protection Measures ----------------------------------------------- 85

2.11 Riverbed Aggradation and Degradation -------------------------------------- 86 2.11.1 What is Aggradation and Degradation? -------------------------------- 86 2.11.2 Degradation Countermeasures ------------------------------------------- 87 2.11.3 Aggradation Countermeasures ------------------------------------------- 88

2.12 Specific Design Considerations ------------------------------------------------- 90 2.12.1 Hydrostatic Force ------------------------------------------------------------- 90 2.12.2 Buoyancy Force --------------------------------------------------------------- 90 2.12.3 Stream Pressure and Lift Force------------------------------------------- 91 2.12.4 Wave Forces ------------------------------------------------------------------- 92 2.12.5 Effects of Debris -------------------------------------------------------------- 92 2.12.6 Effects of Ice ------------------------------------------------------------------- 93 2.12.7 Vessel Collision --------------------------------------------------------------- 94

2.13 Summary of Related Literature Review --------------------------------------- 95

Chapter 3.0 Research Methodology ------------------------------------------------- 97 3.1 General Overview of Research Methods ----------------------------------------- 97 3.2 Research Schedule -------------------------------------------------------------------- 97 3.3 Site Inspection Procedure ------------------------------------------------------------ 98 3.4 Site Investigation Reports ------------------------------------------------------------ 99 3.5 Data Analysis Procedure ------------------------------------------------------------- 99

Chapter 4.0 Site Investigation Reports ------------------------------------------- 100 4.1 Introduction ----------------------------------------------------------------------------- 101 4.2 Locality Map ---------------------------------------------------------------------------- 101 4.3 Bridge Inspection and Site Investigation --------------------------------------- 101 4.4 River Hydraulics and Hydrology -------------------------------------------------- 102 4.5 Geology and Geomorphology ----------------------------------------------------- 102 4.6 Discussions and Recommendations --------------------------------------------- 103

Chapter 5.0 Results and Discussions --------------------------------------------- 104 5.1 General Overview -------------------------------------------------------------------- 104 5.2 Results ----------------------------------------------------------------------------------- 104 5.3 Discussions ----------------------------------------------------------------------------- 104

Chapter 6.0 Conclusion and Recommendations ------------------------------ 107 6.1 Conclusion of the Study ------------------------------------------------------------- 107 6.2 General Flood Resistant Bridge Foundation Design Guidelines --------- 107

References --------------------------------------------------------------------------------- 113

Appendices --------------------------------------------------------------------------------- 114 Appendix A: Department of Works Bridge Inspection Form -------------------- 114 Appendix B: Tensar Geogrid Specification------------------------------------------ 115 Appendix C: Bidim Non-Woven Geotextile ------------------------------------------ 116 Appendix D: Preliminary Bridge Hydraulic Design Process -------------------- 117 Appendix E: FHWA Scour and Stream Stability Flow Chart ------------------- 118

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Appendix F: Standard Template for Scour and Stream Stability Plan of Action -------------------------------------------------------------------------------------------------- 119 Appendix G: PNG Flood Estimation Manual Tables & Figures ---------------- 124

List of Figures Figure 1.0 Flood damaged Surinam Bridge along Ramu Highway in Madang Province ..................... 30 Figure 2.0 Flood damaged Bena Bridge in Eastern Highlands Province ............................................. 33 Figure 3.0 Flood damaged Kumusi Bridge in Oro Province, PNG. ..................................................... 38 Figure 4.0. Typical components of a Bridge Abutment ......................................................................... 41 Figure 5.0 River Channel Flow Constriction Plan ................................................................................ 42 Figure 6.0 Section A - A of the constricted river channel ..................................................................... 42 Figure 7.0 Types of Bridge Pier Shapes ................................................................................................ 45 Figure 8.0 Local scour at bridge pier ................................................................................................... 46 Figure 9.0 Drag and Lift Forces on Bridge Piers ................................................................................. 52 Figure 10.0 Typical Bridge Foundation Details ................................................................................... 54 Figure 11.0 Relationship between wall and earth pressure movement [Clough and Duncan, 1991] ... 59 Figure 12.0 Relationship between compacted backfill wall movement and earth pressure [Clough and

Duncan, 1991] ...................................................................................................................... 59 Figure 13.0 Coulomb Active Earth Pressure Force .............................................................................. 61 Figure 14.0 Coulomb Passive Earth Pressure Force ............................................................................ 62 Figure 15.0 Rankine's Theory for Active Earth Pressure in a Frictionless Wall .................................. 66 Figure 16.0 Caquot and Kerisel Log Spiral Failure Surface ................................................................ 67 Figure 17.0 Active and Passive Pressure Coefficients for Vertical Wall and Horizontal Backfill based

on Log Spiral Failure Surfaces............................................................................................. 68 Figure 18.0 Caquot and Kerisel Active Pressure Coefficient (Ka) Values for Log Spiral Failure

Surfaces ................................................................................................................................ 69 Figure 19.0 Caquot and Kerisel Passive Pressure Coefficient (Kp) Values for Log Spiral Failure

Surfaces ................................................................................................................................ 70 Figure 20.0 Side Elevation at a Bridge Contraction ............................................................................. 80 Figure 21.0 Flow Chart for Scour and Stream Stability analysis and evaluation ................................. 84 Figure 22.0. Shows damaged embankment of Girua Bridge in Oro Province ...................................... 85 Figure 23.0 Aggradation and Degradation in river channel ................................................................ 87 Figure 24.0 Data Analysis Procedure ................................................................................................. 100 Figure 25.0 DoW Bridge Inspection Form. Source: Department of Works – PNG. ........................... 114 Figure 26.0 Tensar Geogrid Specification Notes. Source: Markham Culverts Ltd ............................. 115 Figure 27.0 Geotextile Summary Guide for PNG. Source: Markham Culverts Ltd – PNG. ............... 116 Figure 28.0 Procedure for preliminary hydraulic bridge design. Source: Scottish Design Manual for

Roads and Bridges (1994). ................................................................................................. 117 Figure 29.0 Map of 2-Year Daily Point Rainfall (P2) ......................................................................... 126 Figure 30.0 Map of 100-year Daily Point Rainfall (P100) ................................................................... 127 Figure 31.0 Short Duration Rainfall Generalized Curves for DT,tc/PT Ratio ....................................... 128 Figure 32.0 Tropical Cyclones and Rainfall Seasonality .................................................................... 129 Figure 33.0 Regional Flood Frequency Method Definition of Slope and Shape Indexes ................... 130 Figure 34.0 Regional Flood Frequency Method Swamp Adjustment Factor (KS) .............................. 131 Figure 35.0 Regional Flood Frequency Method Area-P2 Matrix ........................................................ 132 Figure 36.0 Regional Flood Frequency Method Area-Slope Matrix ................................................... 133 Figure 37.0 Regional Flood Frequency Method Slope-P2 Matrix ....................................................... 134 Figure 38.0 Rational Method Frequency Factors ............................................................................... 135

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List of Tables Table 1.0 Common Types of Flooding ................................................................................................... 36 Table 2.0 Flood Damaged Bridges in Papua New Guinea ................................................................... 39 Table 3.0 AASHTO recommended Pier Shape Factor (K) Values ........................................................ 51 Table 4.0 Drag Coefficient (Cd) Value .................................................................................................. 53 Table 5.0 AS5100 Lift Coefficient (CL) Values....................................................................................... 54 Table 6.0 Performance Factors for Shallow Foundations .................................................................... 57 Table 7.0 Approximate Magnitudes of Movements required to reach the Minimum Active and

Maximum Passive Earth Pressure Conditions ..................................................................... 58 Table 8.0 Ultimate Friction Angles US Department of Navy (1982) ..................................................... 63 Table 9.0 Summary of Aggradation and Degradation Countermeasures ............................................. 89 Table 10.0 Tentative Research Schedule ............................................................................................... 97 Table 11.0 Site Inspection General Outline .......................................................................................... 99 Table 12.0. Shows the Table of Results format .................................................................................... 104 Table 13.0. Presents the general flood resistant design guidelines. .................................................... 108 Table 14.0 Short Duration Rainfall Ratios (DT,tc/PT) .......................................................................... 124

List of Equations Equation 1.0 Pier Abutment analogy Method ....................................................................................... 43 Equation 2.0 FHWA Constriction Flow Estimation Method ................................................................. 43 Equation 3.0 Froude Number ................................................................................................................ 43 Equation 4.0 Effective Length of Abutment ........................................................................................... 44 Equation 5.0 FHWA General Scour Estimation Method ....................................................................... 47 Equation 6.0 Scouring due to constriction flow over the Floodplain .................................................... 48 Equation 7.0 Local scour estimation for well-aligned piers.................................................................. 48 Equation 8.0 Melville and Sutherland Method ...................................................................................... 48 Equation 9.0 Colorado State University (CSU) Method ....................................................................... 49 Equation 10.0 Combined Scour Equation ............................................................................................. 50 Equation 11.0 Designed Bed Level Equation ........................................................................................ 50 Equation 12.0 Hydrodynamic Flow Pressure........................................................................................ 51 Equation 13.0 Apelt and Isaacs Drag Force Equation.......................................................................... 52 Equation 14.0 Apelt and Isaacs Lift Force Equation ............................................................................ 52 Equation 15.0 AS5100 Ultimate Design Drag Force ............................................................................ 53 Equation 16.0 AS5100 Serviceability Design Drag Force .................................................................... 53 Equation 17.0 AS5100 Ultimate Design Lift Force ............................................................................... 53 Equation 18.0 AS5100 Serviceability Design Lift Force ....................................................................... 53 Equation 19.0 AASHTO LRFD Equation .............................................................................................. 56 Equation 20.0 AASHTO LRFD maximum Load Modification Factor ................................................... 56 Equation 21.0 AASHTO LRFD minimum Load Modification Factor ................................................... 56 Equation 22.0 Coulomb Active Earth Pressure Force (Pa) ................................................................... 61 Equation 23.0 Active Earth Pressure Coefficient (Ka) .......................................................................... 61 Equation 24.0 Coulomb’s Active Earth Pressure Equation .................................................................. 62 Equation 25.0 Coulomb Passive Earth Pressure Force (Pp) ................................................................. 62 Equation 26.0 Rankine Active Earth Pressure Force (Pa) .................................................................... 64 Equation 27.0 Rankine' Active Earth Pressure Coefficient (Ka) ........................................................... 64 Equation 28.0 Rankine Passive Earth Pressure Coefficient (Kp) .......................................................... 65 Equation 29.0 Rankine Passive Earth Pressure Force (Pp) .................................................................. 65 Equation 30.0 Mannings’s Equation for Open Channel Flow .............................................................. 72 Equation 31.0 Two Year Return Period (Q2) Peak Flood Estimate ...................................................... 74 Equation 32.0 Alternate Two Year Return Period (Q2) Peak Flood Estimate ....................................... 74 Equation 33.0 100-Year Return Period (Q100) Peak Flood Estimate .................................................... 75 Equation 34.0 Alternate Q100 Return Period if Slope only is outside the limits ..................................... 75 Equation 35.0 Alternate Q100 Return Period if both P2 and Slope are outside the limits ...................... 75 Equation 36.0 Flood Discharges of other return periods (QT) .............................................................. 75 Equation 37.0 Rational Flood Design Method ...................................................................................... 76 Equation 38.0 Ramser-Kirpich Formula ............................................................................................... 76

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Equation 39.0 Runoff Coefficient (C2) ................................................................................................... 77 Equation 40.0 USBPR Method .............................................................................................................. 80 Equation 41.0 Velocity Head ................................................................................................................. 81 Equation 42.0 Backwater Coefficient (k)............................................................................................... 81 Equation 43.0 Method of Estimating Afflux depth at Upstream of Arch Bridge ................................... 82 Equation 44.0 Method of Estimating Afflux depth at Downstream of Arch Bridge ............................... 82

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Glossary of Terms Term Definition Abrasion Wearing or grinding away of material by water laden

with sand, gravel, or stones Abutment

A substructure supporting the end of a single span or the extreme end of a multi-span superstructure and, in general, retaining or supporting the approach embankment

Aggradation General and progressive raising of the streambed by deposition of sediment

Aggregate The sand, gravel, or broken stone with which a cementing material is mixed to form a mortar or concrete

Alignment The relative horizontal and vertical positioning between the bridge and approaches

Anchorage

The complete assemblage of members and parts, designed to hold in correct position a portion or part of a structure

Appraisal rating A judgment of a bridge component condition in comparison to current standards

Approach slab

A reinforced concrete slab placed on the approach embankment adjacent to and usually resting upon the abutment back wall.

Apron

A form of scour protection consisting of timber, concrete, riprap, paving, or other construction placed adjacent to abutments and piers to prevent undermining

Armor

A secondary steel member installed to protect a vulnerable part of another member, e.g., steel angles placed over the edges of a joint

AS 5100 Australian Bridge Design Standard Asphalt

Black surface material made from mineral hydrocarbons containing petroleum; the distinction between asphalt and bitumen is mainly chemical, in that asphalt is for solid surfacing and bitumen is a liquid suitable for coating aggregates

ASTM American Society for Testing and Materials AHC Australian High Commission Axial In line with the centroid of the area Axle Load

The load is borne by one axle of a traffic vehicle, a movable bridge, or other motive equipment or device and transmitted through a wheel or wheels

Backfill Material, usually soil used to fill the unoccupied portion of a substructure excavation

Back-wall

The topmost portion of an abutment above the elevation of the bridge seat, functioning primarily as a retaining wall with a live load surcharge; it may serve also as a support for the extreme end of the bridge deck and the approach slab backwater - the water

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upstream from an obstruction in which the free surface is elevated above the normal water surface profile

Bailey Bridge Is a prefabricated kit bridge system comprised of K – Truss steel Panels that makes up the superstructure

Bank Sloped sides of a waterway channel or approach roadway, short for embankment

Bascule Bridge

A bridge over a waterway with one or two leaves which rotate from a horizontal to a near-vertical position, providing unlimited clear headway

Base Plate

A rectangular slab of steel, whether cast, rolled or forged, connected to a column, bearing or another member to transmit and distribute its load to the substructure

Batter

The inclination of a surface in relation to a horizontal or a vertical plane; commonly designated on bridge detail plans as so many feet to one foot

Battered Pile A pile driven in an inclined position to resist horizontal forces as well as vertical forces

Bay The area of a bridge floor system between adjacent multi-beams or between adjacent floor beams

Beam A linear structural member designed to span from one support to another

Bearing

A support element transferring loads from superstructure to substructure while permitting limited movement capability

Bearing Capacity The load per unit area which a structural material, rock, or soil can safely carry

Bearing Failure A crushing of material under extreme compressive load

Bearing Pile A pile which provides support through the tip (or lower end) of the pile

Bearing Pressure The bearing load divided by the area to which it is applied

Bearing Seat A prepared horizontal surface at or near the top of a substructure unit upon which the bearings are placed

Bed Rock The undisturbed hard rock layer below the surface of the soil

Bedding The soil or backfill material used to support pipe culverts

Bench Mark An established reference point used to document dimensions, elevations and movement

Bending Moment The internal force within a beam, which causes a bending effect.

Berm

The line which defines the location where the top surface of an approach embankment or causeway is intersected by the surface of the side slope

Bituminous A black sticky mixture of hydrocarbons obtained from natural deposits or from distilling petroleum

Blanket A stream bed protection against scour placed adjacent to abutments and piers

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Bolt A mechanical fastener with machine threads at one end to receive a nut, and a hexagonal head at the other end

Box Beam A hollow structural beam with a square, rectangular, or trapezoidal cross-section

Box Culvert A culvert of rectangular or square cross-section Bracing A system of secondary members that maintain the

geometric configuration of primary members Breast-wall

The portion of an abutment between the wings and beneath the bridge seat; the breast wall supports the superstructure loads and retains the approach fill.

Bridge A structure carrying a road, path, railroad, or canal across a river, ravine, road, railroad, or another obstacle.

Bridge Deficiency A defect in a bridge component or member that makes the bridge less capable or less desirable for use

Bridge Pad

The raised, levelled area upon which the pedestal, masonry plate or another corresponding element of the superstructure takes bearing by contact; also called bridge seat bearing area

Bridge Seat

The top surface of an abutment or pier upon which the superstructure span is placed and supported; for an abutment, it is the surface forming the support for the superstructure and from which the back-wall rises; for a pier, it is the entire top surface

Bridge Site The selected position or location of a bridge and its surrounding area

Buckle To fail by an inelastic change in alignment as a result of compression

Buoyancy Upward pressure exerted by the fluid in which an object is immersed

Buried Pipe

A subsurface structure that incorporates both the strength properties of the pipe and the support properties of the soil surrounding the pipe

Buttress

A bracket-like wall, of full or partial height, projecting from another wall; the buttress strengthens and stiffens the wall against overturning forces; all parts of a buttress act in compression

Buttressed Wall A retaining wall designed with projecting buttresses to provide strength and stability

Cable

A tension member comprised of numerous individual steel wires twisted and wrapped in such a fashion to form a rope of steel.

Cable-Stayed Bridge

A bridge in which the superstructure is directly supported by cables, or stays, passing over or attached to towers located at the main piers

Caisson A rectangular or cylindrical chamber for keeping water or soft ground from flowing into an excavation

Camber

The slightly arched form or convex curvature provided in beams to compensate for dead load deflection, in

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general, a structure built with perfectly straight lines appears slightly sagged

Cantilever

A structural member which has a free end projecting beyond its supporting wall or column; length of span overhanging the support

Cantilever Abutment

An abutment which resists the lateral thrust of earth pressure through the opposing cantilever action of a vertical stem and horizontal footing

Cantilever Bridge A general term applying to a bridge having a superstructure utilising cantilever design

Cap

The topmost piece of a pier or a pile bent serving to distribute the loads upon the columns or piles and to hold them in their proper relative positions

Cast-In-Place The act of placing and curing concrete within formwork to construct a concrete element in its final position

Catch Basin

A receptacle, commonly box shaped and fitted with a grilled inlet and a pipe outlet drain, designed to collect the rain water and floating debris from the roadway surface and retain the solid material so that it may be periodically removed

Catchment Area Is the drainage area of a bridge site Cellular Abutment

An abutment in which the space between wings, breast wall, approach slab, and footings is hollow. Also known as a vaulted abutment

Cement A powder that hardens when mixed with water; an ingredient used in concrete

Center of Gravity The point at which the entire mass of a body acts; the balancing point of an object

Centroid That point about which the static moment of all the elements of area is equal to zero

Channel

A waterway connecting two bodies of water or containing moving water; a rolled steel member having a C-shaped cross section

Channel Profile A cross-section of a channel along its centerline Clear Headway The vertical clearance beneath a bridge structure

available for navigational use Clear Span The unobstructed space or distance between support

elements of a bridge or bridge member Clearance The unobstructed vertical and horizontal space

provided between two objects Coarse Aggregate Aggregate which stays on a sieve of 5 mm square

opening Cofferdam A temporary dam-like structure constructed around an

excavation to exclude water Column

A general term applying to a vertical member resisting compressive stresses and having, in general, a considerable length in comparison with its transverse dimensions

Compaction The process by which a sufficient amount of energy is applied to soil to achieve a specific density

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Component

A general term reserved to define a bridge deck, superstructure or substructure; subcomponents e.g. floor beams are considered elements

Composite Action The contribution of a concrete deck to the moment resisting capacity of the superstructure beams

Composite Construction

A method of construction whereby a concrete deck is mechanically attached to a steel floor system by shear connectors

Compression A type of stress involving pressing together; tends to shorten a member; opposite of tension

Compression Failure

Buckling, crushing, or collapse caused by compression stress

Concentrated Load

A force applied over a small contact area; also known as point load

Concrete A mixture of aggregate, water, and a binder, usually portland cement, which hardens to a stone-like mass

Concrete Beam A structural member of reinforced concrete Concrete Pile

A pile constructed of reinforced concrete either precast and driven into the ground or cast-in-place in a hole bored into the ground

Consolidation

The time-dependent change in volume of a soil mass under compressive load caused by pore-water slowly escaping from the pores or voids of the soil

Construction Joint A pair of adjacent surfaces in reinforced concrete where concreting was intentionally stopped and continued later

Continuous Beam A general term applied to a beam which spans uninterrupted over one or more intermediate supports

Continuous Bridge A bridge designed to extend without joints over one or more interior supports

Continuous Spans Spans designed to extend without joints over one or more intermediate supports

Continuous Truss

A truss having its chord and web members arranged to continue uninterrupted over one or more intermediate points of support

Contraction The action of drawing together Corbel

A piece constructed to project from the surface of a wall, column or other portion of a structure to serve as a support for another member

Corrosion The general disintegration of surface metal through oxidation

Counterfort

A bracket-like wall projecting from a retaining wall on the side of the retained material to stabilise it against overturning; a counterfort, as opposed to a buttress, acts entirely in tension

Counter-forted Abutment

An abutment, which develops resistance to bending moment in the stem by use of counterforts. This permits the breast wall to be designed as a horizontal beam or slab spanning between counterforts, rather than as a vertical cantilever slab

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Counter-forted Wall

A retaining wall designed with projecting counterforts to provide strength and stability

Counterweight

A weight which is used to balance the weight of a movable member; in bridge applications counterweights are used to balance a movable span so that it rotates or lifts with minimum resistance

Course A layer of bricks or stone bedded in mortar Cover In reinforced concrete, the clear thickness of concrete

between a reinforcing bar and the surface of the concrete; the depth of backfill over the top of a pipe

Covered Bridge An indefinite term applied to a wooden bridge having its roadway protected by a roof and enclosing sides

Crack A break without complete separation of parts; a fissure Cracking Visible cracks in an overlay indicating cracks in the

concrete underneath Creep An inelastic deformation that increases with time while

the stress is constant Crib

A structure consisting of a foundation grillage combined with a superimposed framework providing compartments or coffers which are filled with gravel, concrete or other material satisfactory for supporting the structure to be placed thereon

Cribbing

A construction consisting of wooden, metal or reinforced concrete units so assembled as to form an open cellular-like structure for supporting a superimposed load or for resisting horizontal or overturning forces acting against it

Cross Bracing Transverse bracings between two main longitudinal members.

Cross Girders Girders supported by bearings which supply transverse support for longitudinal beams or girders

Cross Section The shape of an object cut transversely to its length Cross-Sectional Area

The area of a cross-section

Crown

The highest point along the internal surface of the transverse cross section of a pipe or arch; also known as soffit or vortex

Crown of Roadway

The vertical dimension describing the total amount the surface is convex or raised from gutter to centerline; this is sometimes termed the cross fall of roadway

Culvert A drainage structure beneath an embankment Curtain Wall

A term commonly applied to a thin wall between main supports not designed to withstand superimposed loads either vertically or transversely

Cutwater A sharp-edged structure built around a bridge pier to protect it from the flow of water and debris in the water

Dead Load A static load due to the weight of the structure itself Debris Any material including floating wood trash, suspended

sediment, or bed load, moved by a flowing stream

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Deck That portion of a bridge which provides direct support for vehicular and pedestrian traffic

Deck Bridge A bridge in which the supporting members are all beneath the roadway

Deflection Elastic movement of a structural member under a load Deformation Distortion of a loaded structural member; includes

plastic, non-recoverable movement Deformed Bars

Concrete reinforcement consisting of steel bars with projections or indentations to increase the mechanical bond between the steel and concrete

Degradation General progressive lowering of the channel stream bed by erosion

Design Load The force for which a structure is designed; the worst possible combination of loads

Deterioration Decline in quality over a period of time due to chemical or physical action of the environment

Diagonal A sloping structural member of a truss or bracing system

Diagonal Tension The principal tensile force due to horizontal and vertical shear in a beam

Diaphragm

A member placed within a member or superstructure system to distribute stresses and improve strength and rigidity

Differential Settlement

Uneven settlement of individual or independent elements of a substructure

Dike

An earthen embankment constructed to retain floodwater; when used in conjunction with a bridge, it prevents stream erosion and localised scour and so directs the stream current such that debris does not accumulate; also known as a dyke.

Discharge The volume of fluid per unit of time flowing along a pipe or channel

Distributed Load A load uniformly applied along the length of an element or component of a bridge

Dolphin

A group of piles driven close together and placed to protect portions of a bridge exposed to possible damage by collision with river or marine traffic

DoT Department of Transport – Papua New Guinea DoW Department of Works – Papua New Guinea Dowel A short length of bar embedded in two parts of a

structure to hold the parts in place and to transfer stress

Drain Hole

Hole in a box-shaped member or a wall to provide means for the exit of accumulated water or other liquid matter; also known as drip hole

Drain Pipes Pipes below the ground that remove rainwater Drainage A system designed to remove water from a structure Drainage Area

An area in which surface run-off collects and from which it is carried by a drainage system; also known as catchment area

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Drawbridge

A general term applied to a bridge over a navigable body of water having a movable superstructure span of any type permitting the channel to be freed of its obstruction to navigation; popular but imprecise term

Drip Notch

A recess cast on the underside of a parapet which prevents water from following the concrete into the supporting beams and causing deterioration of the members

Drop Inlet

A type of inlet structure which conveys the water from a higher elevation to a lower outlet elevation smoothly without a free fall at the discharge

Ductile Capable of being moulded or shaped without breaking Ductile Fracture A fracture characterised by plastic deformation Ductility The ability to withstand non-elastic deformation

without rupture Dumbbell Pier A pier consisting of two cylindrical or rectangular

shaped piers joined by a web constructed integrally with them

E Modulus of elasticity of a material; the stiffness of a material

Elastic Capable of sustaining deformation without permanent loss of shape

Elastic Deformation

Non-permanent deformation; when the stress is removed, the material returns to its original shape

Elasticity

The property whereby a material changes its shape under the action of loads but recovers its original shape when the loads are removed

Elastomer A natural or synthetic rubber-like material Elongation The elastic or plastic extension of a member Embankment

A bank of earth constructed above the natural ground surface to carry a road or to prevent water from passing beyond desirable limits; also known as bank

End Section

A concrete or steel appurtenance attached to the end of a culvert for the purpose of hydraulic efficiency and anchorage

End-Span A span adjacent to an abutment Equilibrium In statics, the condition in which the forces acting upon

a body are such that no external effect (or movement) is produced

Equivalent Uniform Load

A load having a constant intensity per unit of its length producing an effect equal to that of a live load consisting of vehicle axle or wheel concentrations spaced at varying distances

Erosion Removal of soil by flowing water Expansion An increase in size or volume Expansion Joint

A joint designed to provide means for expansion and contraction movements produced by temperature changes, loadings or other forces

Exterior Girder An outermost girder supporting the bridge floor

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Factor of Safety

A factor applied to the failure stress assumed to exist in a structure to provide a conservative margin in the strength of a structure compensating for irregularities existing in structural materials and workmanship, uncertainties involved in mathematical analysis and stress distribution, service deterioration and other unevaluated conditions

Failure

A condition at which a structure reaches a limit state such as cracking or deflection; usually does not involve fracture since failing structures are deemed unsafe, therefore unusable, before they collapse

False-work

A temporary wooden or metal framework built to support the weight of a structure during the period of its construction and until it becomes self-supporting

Fatigue

The tendency of a member to fail at a lower stress when subjected to cyclical loading than when subjected to static loading

Fatigue Crack Any crack caused by repeated cycle loading Fatigue Damage Member damage (crack formation) due to cyclic

loading Fatigue Life The length of service of a member Fender

A structure that acts as a buffer to protect the portions of a bridge exposed to floating debris and water-borne traffic from collision damage; sometimes called an ice guard in regions with ice flaws

Fender Pier A pier-like structure which performs the same service as a fender but is generally more substantially built

FHWA United States Federal Highway Administration Fill Material, usually earth, used to change the surface

contour of an area or to construct an embankment Fine Aggregate Sand or grit for concrete which passes a sieve mesh

of 5 mm square Fixed End Movement is restrained Fixed Span A superstructure span having its position practically

immovable, as compared to a movable span Flood An overflowing of a large amount of water beyond its

normal confines, especially in a river or stream. Flood Frequency The average time interval in years in which a flow of a

given magnitude will recur Flood Plain Area adjacent to a stream or river subject to flooding Gabion Rock filled wire baskets used to retain earth and

provide erosion control Girder

A flexural member which is the main or primary support for the structure, and which usually receives loads from floor beams and stringers; any large beam, especially if built up

Girder Bridge

A bridge whose superstructure consists of two or more girders supporting a separate floor system as differentiated from a multi-beam bridge or a slab bridge

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Grade The fall or rise per unit horizontal length Gradient

The rate of inclination of the roadway and/or sidewalk surface(s) from horizontal applying to a bridge and its approaches; it is commonly expressed as a percentage relation of horizontal to vertical dimensions

Gravity Abutment A heavy abutment which resists horizontal earth pressure through its own dead weight

Gravity Wall A retaining which is prevented from overturning its weight alone

Groin A wall built out from a river bank to check scour Guardrail A safety feature element intended to redirect an errant

vehicle - away from the approach embankment H-Beam A rolled steel member having an H-shaped cross

section and commonly used for piling Head

A measure of water pressure expressed in terms of an equivalent weight or pressure exerted by a column of water; the height of the equivalent column of water is the head

Head-loss The loss of energy between two points along the path of a flowing fluid due to fluid friction reported in feet of head

Headwall

A concrete structure at the ends of a culvert to protect the embankment slopes, anchor the culvert and prevent undercutting

Headwater The source or the upstream waters of a stream High Strength Bolt Bolt and nut made of high strength steel, usually A325

or stronger Hinged Joint

A joint constructed with a pin, cylinder segment, spherical segment or other device permitting movement by rotation

Horizontal Cracks Cracks which are parallel to the longitudinal axis of the member and thus parallel to the primary stress

Hydraulics The mechanics of fluids, primarily water Hydrology

The science of water related to its properties and distribution in the atmosphere, on the land surface, and beneath the surface of the land

Hydroplaning

Loss of contact between a tire and the deck surface when the tire planes or glides on a film of water covering the deck

I-Beam A structural member with a cross-sectional shape similar to the capital letter "I"

Impact Amplification effect on live load due to dynamic and vibratory effects of a moving load

Inelastic Compression

Compression beyond the yield point

Inlet An opening in the floor of a bridge leading to a drain Inspection Frequency

The frequency with which the bridge is inspected - normally every two years

Integral Abutment

An abutment cast monolithically with the end diaphragm of the deck; such abutments usually

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encase the ends of the deck beams and are pile supported

Integral Deck

A deck which is design to share with the superstructure, the load carrying capabilities of the bridge and not merely to transfer loads to the superstructure

Intercepting Ditch

A ditch constructed to prevent surface water from flowing in contact with the toe of an embankment or causeway or down the slope of a cut

Inventory Item

Data contained in the structure file pertaining to bridge identification, structure type and material, age and service, geometric data, navigational data, classification, load rating and posting, proposed improvements, and inspections

Invert The bottom or lowest point of the internal surface of the transverse cross section of a pipe

Joint

In stone masonry, the space between individual stones; in concrete, a division in continuity of the concrete; in a truss, point at which members of a truss frame are joined

K-Truss

A truss having a web system wherein the diagonal members intersect the vertical members at or near the mid-height; the assembly in each panel forms a letter "K"

Lateral Bracing

The bracing assemblage engaging a member perpendicular to the plane of the member; intended to resist lateral movement and deformation; also provides resistance against raking movement of primary parallel elements in truss bridges and girder bridges

Levee An embankment built to prevent flooding of low-lying land

Light-Weight Concrete

No-fines concrete, aerated concrete, or concrete made of lightweight aggregate

Live Load

A dynamic load such as vehicular traffic that is applied to a structure suddenly; also accompanied by vibration or movement affecting its intensity

Load The weight carried by a structure Load Rating

An office exercise to determine the ability of a bridge to carry load based on the conditions reported by an inspector

Longitudinal Bracing

Bracing that runs lengthwise with a bridge and provides resistance against longitudinal movement and deformation of transverse members

Main Beam A beam which supports the span and bears directly onto a column or wall

Masonry

That portion of a structure composed of stone, brick or concrete block placed in layers and in some cases cemented with mortar

Masonry Cement A cement, usually Portland, that hardens slowly and holds water well

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Mattress

A mat-like protective covering composed of brush and poles compacted by wire and placed upon river beds and banks to prevent erosion and scour by stream flow

MDG Millennium Development Goals Meander

A twisting, winding action from side to side; characterises the serpentine curvature of a narrow, slow flowing stream in a wide flood plain

Member

An individual angle, beam, plate, or built piece intended ultimately to become an integral part of an assembled frame or structure

Mid-span A general reference point half-way between the supports of a beam or span

Moisture Content The amount of water in a soil mass expressed as a percent by weight

Moment The coupling effect of forces about a given point Monolithic Forming a single mass without joints Mortar A paste of cement, sand, and water laid between

bricks, stones or blocks Movable Bridge

A bridge having one or more spans capable of being raised, turned, lifted, or slid from its normal service location to provide for the passage of navigation

Moving Load A live load which is moving, for example, vehicular traffic

NBIS

National Bridge Inspection Standards, first established in 1971 to set national policy regarding bridge inspection frequency, inspector qualifications, report formats, and inspection and rating procedures

Necking The elongation and contraction in area which occurs when a ductile metal fails in tension

Nose A projection acting as a cutwater on the upstream end of a pier

Out-of-Plane Distortion

Distortion of a member in a plane other than that which the member was designed to resist

Outlet In hydraulics, the discharge end of drains, sewers, or culverts

Overload A weight greater than the structure is designed to carry

Overturning Tipping over, rotational movement Panel The portion of a truss span between adjacent points of

intersection of web and chord members Parapet A low wall along the outmost edge of the roadway of a

bridge to protect vehicles and pedestrians Pedestal

Concrete or built-up metal member constructed on top of a bridge seat for the purpose of providing a specific bearing seat elevation

Penetration

When applied to creosoted lumber, the depth to which the surface wood is permeated by the creosote oil; when applied to pile driving; the depth a pile tip is driven into the ground

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Pier

A substructure unit that supports the spans of a multi-span superstructure at an intermediate location between its abutments

Pier Cap The topmost portion of a pier which distributes uniformly over the pier the concentrated loads from the bridge

Pile

A shaft-like linear member which carries loads through weak layers of soil to those which are capable of supporting such loads

Pile Bent A row of driven or placed piles with a pile cap to hold them in their correct positions

Pile Bridge A bridge carried on piles or pile bents Pile Cap

The uppermost portion of a pile which acts to secure the piles in position and provides a bridge seat to receive and distribute superstructure loads

Pile Foundation

A foundation reinforced by driving piles in sufficient number and to a depth adequate to develop the bearing resistance required to support the substructure load

Piling General term applied to group of piles in a construction

Pin A cylindrical bar used to connect Pin Joint A joint in a truss or other frame in which the members

are assembled upon a cylindrical pin Pin-Connected Truss

A general term applied to a truss of any type having its chord and web members connected at the panel points by pins

Pipe A hollow cylinder used for the conveyance of water, gas, steam etc.

Plain Concrete Concrete with no structural reinforcement except light steel to reduce shrinkage and temperature cracking

Plan Drawing that represents the top view of a structure and structure site

Pneumatic Caisson

A caisson in which the working chamber is kept full of compressed air at a pressure nearly equal to the water pressure outside it

PNG Papua New Guinea PNG Vision 2050

A detailed outline of the vision statements of Papua New Guinea National Government to achieve its goals and aspirations to be in top 50 countries of the world according to Human Development Index in the year 2050

Ponding Water backed up in a channel or ditch as the result of a culvert of inadequate capacity

Portable Bridge

A bridge that may be readily erected for a temporary communication-transport service disassembled and its members again reassembled and the entire structure rendered ready for further service

Portal The clear unobstructed space of a through truss bridge forming the entrance to the structure

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Portal Bracing A system of sway bracing placed in the plane of the end posts of the

Post

A member resisting compressive stresses, located vertical to the bottom chord of a truss and common to two truss panels; sometimes used synonymously for vertical

Pratt Truss

A truss with parallel chords and a web system composed of vertical posts with diagonal ties inclined outward and upward from the bottom chord panel points toward the ends of the truss; also known as N-truss

Pre-stressed Concrete

Concrete in which cracking and tensile forces are greatly reduced by compressing it with tensioned cables or bars

Pre-stressing Applying forces to a structure to deform it in such a way that it will withstand its working loads more effectively

Pre-tensioning

A method of pre-stressing concrete in which the cables are held in a stretched condition until the concrete has hardened, then the pull on the cables is released inducing internal compression into the concrete

Precast Concrete

Concrete members which are cast and cured before being placed into their final positions on a construction site

Protective System

A system used to protect bridges from environmental forces that cause steel and concrete to deteriorate and timber to decay, typically a coating system

Punching Shear Shear stress in a slab due to the application of a concentrated load

Quality Assurance

An independent evaluation of a service (i.e., an inspection) to establish that a pre-described level of quality has been met

Quality Control Checks necessary to maintain a uniform level of quality

Railing

A fence-like construction built at the outermost edge of the roadway or the sidewalk portion of a bridge to protect pedestrians and vehicles

Ramp An inclined traffic-way leading from one elevation to another

Reaction The resistance of a support against the pressure of a loaded member

Reinforced Concrete

Concrete with steel reinforcing bars bonded within it to supply increased tensile strength and durability

Reinforced Concrete Pipe

A concrete pipe designed with reinforcing bars to increase its surcharge-carrying capability

Reinforcement Rods or mesh embedded in concrete to strengthen it Reinforcing Bar

A steel bar, plain or with a deformed surface, which bonds to the concrete and supplies tensile strength to the concrete

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Retaining Wall A structure designed to restrain and hold back a mass of earth

Rigid Frame A structural frame in which the members are connected together without hinges

Rip-Rap

Gabions, stones, blocks of concrete or other protective covering material of like nature deposited upon river and stream beds and banks, lake, tidal or other shores to prevent erosion and scour by water flow, wave or another movement

Roadway The portion of the road intended for the use of vehicular traffic

Roller A steel cylinder intended to provide longitudinal movements by rolling contact

Rubble Irregularly shaped pieces of stone in the undressed condition obtained from a quarry and varying in size

Runoff The part of precipitation which flows from a catchment area past a given point over a certain period

Safe Load The load which a structure can safely support Sag To sink or bend downward due to weight or pressure Scour Erosion of a river bed area caused by stream flow Scour Protection

Protection of submerged material by steel sheet piling, rip rap, a mattress, or combination of such methods

Scupper

An opening in the floor portion of a bridge to provide means for rain or other water accumulated upon the roadway surface to drain through it into space beneath the structure

Seat A base on which an object or member is placed Seepage The slow movement of water through a material Segregation The state of being separated Shear The load acting on a beam near its support Shear Stress The shear force per unit of cross-sectional area; also

referred to as diagonal tensile stress Sheet Piles

Flattened Z-shaped interlocking piles driven into the ground to keep earth or water out of an excavation or to protect an embankment

Sheet Piling

A general or collective term used to describe a number of sheet piles installed to form a crib, cofferdam, bulkhead, etc.; also known as sheeting

Shoe

A pedestal-shaped member beneath the superstructure bearing that transmits and distributes loads to the substructure bearing area

Sidewalk The portion of the bridge floor area serving pedestrian traffic only

Silt

Very finely divided siliceous or other hard rock material removed from its mother rock through erosive action rather than chemical decomposition

Simple Span The span of a bridge or element which begins at one support and ends at an adjacent support

The angle produced when the longitudinal members of a bridge are not perpendicular to the substructure; the

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Skew Angle skew angle is the acute angle between the alignment of the bridge and a line perpendicular to the centerline of the substructure units

Slab A flat beam, usually of reinforced concrete, which supports load by flexure

Slab Bridge

A bridge having a superstructure composed of a reinforced concrete slab constructed either as a single unit or as a series of narrow slabs placed parallel with the roadway alignment and spanning the space between the supporting abutments

Slide A sliding down of the soil on a slope because of an increase in load or a removal of support at the foot; also known as landslide

Slope The inclination of a surface expressed as one unit of the rise and fall for so many horizontal units

Slope Protection

A thin surfacing of stone, concrete or other material deposited on a sloped surface to prevent its disintegration by rain, wind or other erosive action

SMEC Snowy Mountain Engineering Company Sounding Determining the depth of water by an echo-sounder or

sounding line Span

The distance between the supports of a beam; the distance between the faces of the substructure elements; the complete superstructure of a single span bridge or a corresponding integral unit of a multiple span structure

Specifications

A detailed description of requirements, materials, dimensions, etc. for a bridge which cannot be shown on the drawings; also known as specs

Spread Footing

A footing which is wide and usually made of reinforced concrete; ideally suited for foundation material with moderate bearing capacity

Spur Dike

A projecting jetty-like construction placed adjacent to an abutment to prevent stream scour and undermining of the abutment foundation and to reduce the accumulation of stream debris against to the upstream side of the abutment

Statics The study of forces and bodies at rest Steel An alloy of iron, carbon, and various other elements

and metals Stem The vertical wall portion of an abutment retaining wall,

or solid pier Stirrup

U-shaped bar providing a stirrup-like support for a member in timber and metal bridges; U- shaped bar placed in concrete constructions to resist diagonal tension (shear) stresses

Stone Masonry The portion of a structure composed of stone Straight Abutment

An abutment whose stem and wings are in the same plane or whose stem is included within a length of retaining wall

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Strain

The change in length of a body produced by the application of external forces, measured in units of length; this is the proportional relation of the amount of change in length divided by the original length

Stress The force acting across a unit area in a solid material Stringer A longitudinal beam supporting the bridge deck Structural Analysis An analysis of a structure (bridge) to determine the

interaction of members and their consequent stresses Structural Member An individual piece, like a beam or strut, which is an

integral part of a structure Structural Stability

The ability of a structure to maintain its normal configuration, not collapse or tip in any way, under existing and expected loads

Structure Something, such as a bridge, that is built and designed to sustain a load

Substructure The abutments, piers, or other constructions built to support the span of a bridge superstructure

Super-Elevation

The difference in elevation between the inside and outside edges of a roadway in a horizontal curve; required to counteract the effects of centrifugal force

Superimposed Dead Load

Dead load that is applied to a bridge after the concrete deck has cured; for example, the weight of parapets or railings placed after the concrete deck has cured

Superstructure

The entire portion of a bridge structure which primarily receives and supports traffic loads and in turn transfers these loads to the bridge substructure

Suspension Bridge

A bridge in which the floor system is supported by catenary cables which are supported by towers and are anchored at their extreme ends

Suspension Cable

A catenary cable which is one of the main members upon which the floor system of a suspension bridge is supported

Sway Bracing

Diagonal bracing located at the top of a through truss, perpendicular to the truss itself and usually in a vertical plane, to resist horizontal forces

Temporary Bridge A structure built for emergency or interim use to replace a previously existing bridge rendered unserviceable

Tensile Force A force caused by pulling at the ends of a member Tensile Strength The maximum load at which a specimen breaks under

tension Tension Type of stress involving an action which pulls apart Thermal Movement

Movement of a bridge structure due to a change in temperature

Through Bridge A bridge where the floor elevation is nearly at the bottom and traffic travels between the supporting parts

Toe

The front portion of a footing from the intersection of the front face of the abutment to the front edge of the footing; the line where the side slope of an embankment meets the existing ground

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Toe of Slope

The location defined by the intersection of the embankment with the surface existing at a lower elevation; also known as toe

Toe Wall

A relatively low retaining wall placed near the "toe-of-slope" location of an embankment to protect against erosion or to prevent the accumulation of stream debris; also known as foot-wall

Ton A unit of weight equal to 2,000 pounds Torque The angular force causing rotation Torsion Twisting perpendicular to the longitudinal axis of a

member Tower A pier or frame supporting the catenary cables of a

suspension bridge Traffic Control Modification of normal traffic patterns by signs, cones,

flagmen, etc. Truss

A jointed structure made up of individual members arranged and connected usually in a triangular pattern, so as to support longer spans

Truss Bridge A bridge having a pair of trusses for a superstructure Tunnel An underground passage, open to daylight at both

ends Ultimate Strength The highest stress which a material can withstand

before breaking Uniform Load A constant load across a member Unit Stress The stress per unit of surface or cross-sectional area Uplift A negative reaction or a force tending to lift a beam,

truss, pile, or any other bridge element upwards Upper Chord The top longitudinal member of a truss Vertical Curve A sag or crest in the profile of a roadway Viaduct A series of spans carried on piers at short intervals Vibration The act of vibrating concrete to compact it Voided Slab A precast concrete deck unit containing cylindrical

voids to reduce dead load Voids An empty or unfilled space in concrete Warren Truss

A triangular truss consisting of sloping members between the top and bottom chords and no verticals; members form the letter W

Washer A small metal ring used beneath the nut or the head of a bolt to distribute the pressure

Water/Cement Ratio

The weight of water divided by the weight of cement in a concrete; ratio controls the strength of the concrete

Waterway The available width for the passage of water beneath a bridge

Wearing Surface

The topmost layer of material applied upon a roadway to receive the traffic loads and to resist the resulting disintegrating action; also known as wearing course

Web The portion of a beam located between and connected to the flanges; the stem of a dumbbell type pier

Weep-hole A hole in a concrete retaining wall to provide drainage of the water in the retained soil

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Welded Bridge Structure

A structure whose metal elements are connected by welds

Welded Joint A joint in which the assembled elements and members are united through fusion of metal

Wheel Load

The load carried by and transmitted to the supporting structure by one wheel of a traffic vehicle, a movable bridge, or other motive equipment or device

Wind Bracing The bracing systems which function to resist the stresses induced by wind forces

Wing-wall

The retaining wall extension of an abutment intended to restrain and hold in place the side slope material of an approach roadway embankment

Wire Mesh Reinforcement

A mesh made of steel wires welded together at their intersections used to reinforce concrete

Working Stress The unit stress in a member under service or design load

Yield Permanent deformation (permanent set) which a metal piece takes when it is stressed beyond the elastic limit

Yield Stress The stress at which noticeable, suddenly increased deformation occurs under slowly increasing load

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Chapter 1.0 Introduction

1.1 Background to Study Bridge failures due to flooding are common and are ever present all around the globe in the recent past. The effects and aftermath of the flood disasters damaging vital infrastructures such as bridges are so detrimental in Papua New Guinea that it warrants a thorough research and study to improve design and construction of bridges that are prone to be affected by flooding natural rivers and streams. Most floods today are caused by typhoons, tropical cyclones, tornadoes, hurricanes or strong winds as a result of climate change. Many today have come to conclude that all these natural disasters are the direct or indirect cause of climate change effects, which have changed the global climatic pattern.

Figure 1.0 Flood damaged Surinam Bridge along Ramu Highway in Madang Province

As seen in the signing of the Paris Agreement on Climate Change by world leaders to decrease the rate of carbon emission into the atmosphere in September 2016. The effects of climate change causing devastating disasters is now a major focus on global front and as engineers, we are entrusted with more responsibility to provide innovative ideas into engineering and technology that can be sustainable to the lives of people using the infrastructure. Whether it is an effect of climate change or an occurrence of a natural phenomenon, we need to provide solutions to counterbalance these forces of nature, especially the flooding waters that cause damage to the vital structures such as bridges in this study.

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1.2 Problem Statement Working against nature is always a challenging task for an engineer trying to design a most workable solution in any given project. As nature surprises us with so many wonderful creations, thus it amazes us with so many challenging issues as we try to adapt to the environment that we live in. Application of numerous engineering techniques to restore the flood damaged and affected bridges have not lasted the test of time in Papua New Guinea. The damages to road bridges by the flood are so frequent that it warrants more detailed investigation and research to determine the causes of failure to the bridges along the main economic highways and rural roads to provide solutions in the design and construction of bridges. The damage of bridges has been observed to be mainly at its foundations. More specifically, the flooding waters wash away the abutments and damage the structure or scour the abutments and piers to weaken the load capacity and eventually destroy the bridge. In addition, it is also attested that bank and embankment erosion by flooding rivers and subsequent leading to the further damage of the bridge structure has been accepted widely in Papua New Guinea. These damages have caused the Government huge sum of funding outside of its budgetary allocations when undertaking emergency restoration works all in the name of providing vital government services as reported by Australian High Commission in PNG (November 2014). However, there is no adequate solution to this problem of flood-damaged bridges, thus giving rise to this research.

1.3 Purpose of the Research The main purpose or rationale of this research is to develop a Flood Resistant Bridge Design policy document after determining the flood resistant bridge design techniques, philosophies and methods from the study. This policy will be formally approved and implemented by Department of Work – PNG that will provide flood resistant bridge design guidelines for bridge designers and contractors to design and construct flood resilient structures in Papua New Guinea. The Loop PNG News Reporter, Yagi (Oct 2015) reported that many business operators have made losses in their businesses, developers such as Marengo and Kurumbu-Kari Mine (Nickel & Copper Mine) in Madang Province of Papua New Guinea have failed to implement projects on time leading to huge company losses. Many government services such as schools and hospitals have been badly disrupted due to damaged bridges along these important roads that link them. Hence, similar related rationales to this study and why this research topic was selected are that Papua New Guinea do not have Bridge Design Standards and Codes and have been adopting Australian and New Zealand Standards (AS5100) when undertaking Bridge Designs. Secondly, Papua New Guinea Bridge Designers and Consultants have been using Flood Estimation Manual prepared by SMEC (Snowy Mountain Engineering Company) for Papua New Guinea Department of Environment, Conservation and Bureau of Water

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Resources produced in 1990 when designing bridge hydraulics and hydrology. The manual provides flood estimation methods ranging to 100 year Flood Return Period, in which most of the bridges designed in accordance with the manual have been damaged by flood and warrants a review to the guide to have current climatic conditions since the beginning of climate change. All in all, Papua New Guinea urgently requires design and construction standards and specifications of major infrastructures to be flood resilient such as bridges in this case. There are no bridge design specifications and this research will provide flood resistive bridge design guidelines to the Government and Transport Organisations to use in future bridge designs through a policy paper.

1.4 Scope of the Research The research scope will be undertaken in two folds, theory and field study. The field study will be undertaken at the flood damaged and affected bridge sites in Japan to collect field data and undertake bridge inspections and investigation, structural assessment and analysis of the substructure and superstructure to determine their failure cases. This research will collaborate with Papua New Guinea Department of Works, Consulting Companies in Japan and Papua New Guinea who have undertaken bridge investigations and designs on the affected bridges, Contractors who constructed the bridges and other relevant government bodies that the scope of this study covers. The site investigations help will determine the bridge structures that were affected or damaged by flood events and provide design guidelines on how to improve the affected bridge structures in the design process to be more flood defiant during the service stage of the structure. The theoretic nature of the study will be more into research of literature of similar studies conducted around the globe and the selection of effective solutions that is within the requirements of Papua New Guinea with regards to flood-damaged bridges in this research.

1.5 Hypothesis The hypothesis to this research is “How can we improve flood affected bridge foundations in Papua New Guinea?”

1.6 Importance of Study Definition of Bridge Before we go into the heart of this study, let us define the word Bridge and understand what bridge is. By the way, one who is not familiar with the word bridge would ask, “What is a bridge? And why is it so important to the livelihood of the people?

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According to New Oxford American Dictionary, a bridge is a structure carrying a road, path, railroad, or canal across a river, ravine, road, railroad, or other physical and natural obstacle. More importantly, as we see in the definition, the bridge is a vital structure that connects two physical or natural barriers like rivers, canals or valleys. And, when a bridge is damaged by flood or any other action, people cannot access the other end of the world that may have vital services like shops, banks, seaports, airports, businesses, etc., which does affect the livelihood of people in an enormous way or even lives are lost while struggling to negotiate through it. Therefore, this research is so vital as frequent bridge damaged by flood in Papua New Guinea has affected many major companies that depend entirely on road transport to have access to major shipping ports, business sites that have made huge company losses. This has caused the company’s profit losses and unaccounted expenses in operating business in Papua New Guinea. Failing transport infrastructure gives a bad image on the investor confidence in any country.

During the collapse of Bena Bridge in Eastern Highlands Province of Papua New Guinea along the main Highlands Highway, the Depot Manager of Puma Energy a fuel supplying company to the mine sites and towns in the Highlands Region, Mr. John Wamp told Post-Courier that the company was running short of fuel to supply to its customers as their fuel trucks were left stranded waiting for the bridge to be fixed. This is an ongoing dilemma encountered by many government service providers and private business all around the ground during the bridge failures. Our road network does not have alternate routes in case of such emergencies; thus, it becomes unbearable during the phenomenon. The daily life of a rural Papua New Guinean is made very difficult when vital infrastructure like roads and bridges are damaged. Eighty percent (80%) of the

Figure 2.0 Flood damaged Bena Bridge in Eastern Highlands Province

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population live in rural areas of the country, which is very rugged terrain and mountainous in nature within the hinterlands. Furthermore, most of this rural populace heavily depends on the road transport to ferry their agricultural produce to sell to the markets in towns and cities and have access to essential government services. Social and economic developments are also denied such as Students, Teachers, Health Workers and Sick Patients cannot access basic education and health care services, as their basic access to the service centre is now affected due to the flood-damaged bridge. Economically, poor road infrastructure such as bridge collapse has cost the government to spend more than the budgeted amount to provide basic services to the people with considerable loss on the revenue generating government businesses. This has contributed to the government’s lack in implementing the many fiscal government policies like Millennium Development Goals (MDGs), Medium Term Development Plan (2011-2017), Development Strategic Plan (2010-2030) and the PNG Vision 2050. Thus, the outcome of this research and its recommended flood resistant design improvements is more important and valuable as a bee is to the honeycomb.

1.7 Study Limitations This research is relevant to the case scenarios faced in Papua New Guinea and will be carried out in Japan. It is limited to natural rivers, creeks and stream bridges damaged by river flooding within the designed discharge or design flood return period. The researcher is unable to undertake site investigations, assessments and information gathering in the country where this report is addressing due to scholarship program limitations of this study. However, all case studies, site investigations and assessments of flood-damaged bridges will be undertaken in Japan in some of the flood affected bridge sites considered to be relevant to this study. After the flood assessments are carried out, the data collected will form the basis of flood resilient bridge design policy development. In some cases, the time period after the flood and the time of inspection for this study may be quite extensive, which can have an impact on the accuracy of site investigation and data collection. Finally, there are three types of flooding that mainly affect the bridge structures during adverse weather conditions, which are:

a) River Flooding b) Flash Flooding, and c) Ocean Flooding.

This study will delve into bridges that have been affected by River and Flash Flooding in Papua New Guinea and undertake investigations and make improvements in the design of the structure.

1.8 Preview of this Study The preview of the research will be as follows:

Chapter 2.0 Related Literature Review Chapter 3.0 Research Methodology Chapter 4.0 Site Investigation Reports

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Chapter 5.0 Bridge Modeling and Experiment Chapter 6.0 Results and Discussions Chapter 7.0 Conclusion and Recommendations

Chapter 2.0 Theory and Literature Review

2.1 Introduction It is widely accepted that the critical infrastructure must be designed, located, and or sufficiently protected to remain operational during an emergency, including floods, storm surges and power outages, or for long-term sustainability. With the recent climate change effects, flooding is becoming more frequent than ever estimated. Many vital infrastructures now are vulnerable to be damaged during flood events, such as bridges in this case. Snell, Smith (2012, p. 1) debated that the damage was done to bridges and their approach embankments during the major floods in South Africa, Mozambique and Zimbabwe suggests that a review of bridge design procedures be implemented. This statement in itself clearly states that there is now a big need on a global scale to review the bridge design methods and techniques used in flood and storm assessment as it is now experienced everywhere in any country today. The time you turn on your TV or radio, there is news about a natural disaster that involves flood in many parts of the world. Flooding is becoming so frequent due to the climate change pattern that we experience today and it is destroying essential infrastructures, homes and killing lives of people more than a civil war or a deadly disease such as AIDS or Cholera in a world scale. The latest news of Hurricane Mathew, which has destroyed hundreds of lives in Haiti and parts of the southeastern coast of USA, is a fact to this discussion. Large scale frequent flooding is becoming a global phenomenon in the recent times. Snell, Smith (2012, p.2) further stated that our concepts in handling floods at bridges, specifically in relation to the design of approach embankments, abutment fills and scour protection facilities must be relooked. Thus, this research will look more detail in improving the design guidelines of bridges such as bridge superstructure, bridge abutments; bridge piers and bank protection work so that the structure can withstand the estimated designed flood events in the service life of the structure. We cannot get rid of rain nor flood, all we can do is re-look on our engineering techniques and technology that we have today and refine them to best fit the action of flood against the bridges that we have and to be built in future. As we have made a breakthrough in earthquake resistive bridge design methods and its application to our experiences with earthquakes, I believe flood resistive bridge design is achievable and this research will provide a light to a further development in this direction.

2.2 Flood What is a flood? According to New Oxford American Dictionary, the flood is an overflowing of a large amount of water beyond its normal confines, especially

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over what is normally dry land. In this study, we will define flood as overflowing of a large body of water beyond its natural clear water level or main river channel. There are three main types of flooding:

River Flooding after a long period of heavy rainfall, Flash Flooding after heavy rainfall over a short duration, and Ocean Flooding, which is an unusual inflow of seawater onto land. This

is mainly caused by storms such as hurricanes (storm surge), high tides (tidal flooding), seismic events (tsunami) or large landslides.

Table 1.0 Common Types of Flooding

Ocean Flooding

Flash Flooding

River Flooding

This study will mainly focus on River Flooding and Flash Flooding in a natural river or stream, as these are the common flood types experienced in Papua New Guinea. River and flash flooding usually results from abnormally high

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rainfall over a relatively short period such as in hours for flash floods and days for river floods. Rapid snowmelt can bring more water into the hydrological system than can be adequately drained, leading to what is generally called spring floods. Heavy rainfall during the tropical rainy season can lead to monsoon floods, which can affect rivers and may also occur as flash flooding. Interestingly, the sedimentation of riverbeds and deforestation of water catchment areas can exacerbate conditions leading to river valley floods. Deforestation and paving over land can significantly increase the risk of flash floods. Building in flood plains or in environmentally degraded areas and changing the natural drainage systems, can significantly increase the risk of flood damage. Thus, all these conditions must be investigated during the initial bridge design stage and require hydrology experts to undertake detail assessment with the help of other specialists. Richard Davies, a News Reporter with Floodlist Asia, published on 16th October 2016 that Papua New Guinea is vulnerable to both inland and coastal flooding. The country has suffered from severe coastal flooding in 2008 as many as 75,000 people were displaced from eight (8) different provinces. Earlier this year (2016), around 10,000 people were affected by flooding in West New Britain Province with thirty-five (35) houses; bridges, roads and agricultural farms were damaged across both provinces of Gulf and Southern Highlands. Rain and its effect of flooding are a natural phenomenon and are here to stay whether we like it or not. It will continue to affect the livelihood of people as long as the natural law of Water Cycle exists. The only way out to reduce and provide a sustainable solution is an innovative way of engineering and technology and better flood mitigation planning. And this is now the course of this research, where we can innovate new methods of bridge design that can withstand the predicted flood events.

2.3 History of Bridge Damaged by Flood According to United States Federal Highway Administration (FHWA), Hydraulic Engineering Circular No. 18 (2012) published that the most common cause of bridge failures in the USA is from floods scouring bed material from around bridge foundations. During the spring floods of 1987, 17 bridges in New York and New England were damaged and destroyed by scouring. In 1985, floods in Pennsylvania, Virginia, and West Virginia destroyed 73 bridges. A national study for the Federal Highway Administration (1973) revealed that catastrophic floods caused 383 bridge failures in the US. Furthermore, of these bridge failures, twenty-five percent (25%) involved pier damage and seventy-five percent (75%) were abutment damage (FHWA, 1973). A second more extensive study in 1978 indicated that local scour at bridge piers was a problem about equal to abutment scour problems (FHWA, 1978). The flooding rivers than any other action caused most of these bridge failures in the US and many other countries. The antiquity of bridges damaged by a flood in Papua New Guinea dates back to the prehistoric days when a man have not invented these modern style

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bridges like Cable-Stayed Bridges, Suspension Bridges, Arch Bridges, Truss Bridges and etc. It was when local people used logs and vines to weave the first ever-manmade temporary bridges in the forests and jungles of Papua New Guinea as the country has the third largest rainforest in the world. The most common type of bridge in Papua New Guinea is a steel truss panel bridge system manufactured in Britain by Mabey Group of Companies and named after its inventor Sir Donald Bailey in World War I and II known as Bailey Bridge. The bridge is common as the national government introduced bridging the community program in 2002, which resulted in the engagement of Mabey Group of Companies to supply and construct bridges across the main highways, district roads and local community roads right across the country where it was applicable. The program was successfully carried out and most communities were linked through the bridge program.

Figure 3.0 Flood damaged Kumusi Bridge in Oro Province, PNG.

However, during the service stage of these bridges, it has now become that most of them have been badly damaged by flooding waters completely or structurally affected at the bridge abutment and approaches as can be seen in Figure 3.0 above. This can be assumed that there was no adequate hydraulics and hydrological investigation and studies carried out on those bridge sites before construction or maybe the structure were built on the poor foundation. According to the records held by Department of Works and Implementation in Papua New Guinea, an agency of the government responsible for roads, bridges and rural infrastructure has shown more bridge damage caused by flooding action of the river than any other means of bridge failure. The table below (Table 1.0) gives an estimated figure of bridges that have been damaged by flooding rivers in Papua New Guinea in the last Five (5) Years in each province.

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Table 2.0 Flood Damaged Bridges in Papua New Guinea

No. Provinces of PNG Number of Bridges 1 Autonomous Region of

Bougainville 20

2 Central 12 3 East New Britain 5 4 East Sepik 15 5 Eastern Highlands 13 6 Enga 8 7 Gulf 7 8 Hela 9 9 Jiwaka 4

10 Madang 25 11 Manus 6 12 Milne Bay 7 13 Morobe 23 14 National Capital District 0 15 New Ireland 16 16 Oro 25 17 Sandaun 14 18 Simbu 11 19 Southern Highlands 18 20 West New Britain 24 21 Western 4 22 Western Highlands 19

Total number of Bridges 280 Bridges Source: Papua New Guinea Department of Works As given in the table above, the number speaks for itself, as this study is so eminent to address the problem of flood-damaged bridges. Most of these damaged bridges have not been maintained and are still waiting for funding from the government since they were damaged. The cost of reconstruction is very high and with economic crisis faced in the country due to a decrease in the world market prices, this is now a dilemma for poor local people. Infrastructure managers are always faced with the challenge to get the affected structure fixed for public use, however, they are always affected by the little funding allocation to repair these damages. Innovative engineering techniques using affordable construction material and simple engineering construction methods are way forward for a developing country such as PNG in meeting its everyday challenges such as this.

2.4 Bridge Abutment Design Bridge Abutment is a substructure member supporting the end of a single span or the extreme end of a multi-span bridge superstructure and, in general, retaining or supporting the approach embankment. Single-span bridges have abutments at each end, which provide vertical and lateral support for the bridge, as well as acting as retaining walls to resist lateral movement of the earthen fill

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of the bridge approach. Multi-span bridges require piers to support ends of spans unsupported by abutments. An abutment performs the following functions:

a) Transfer loads from a superstructure to its foundation elements, b) Resist and transfer self-weight lateral loads such as the earth pressure,

wind and earthquake loads, and c) Support one end of an approach slab.

Abutments are equivalent to stump posts, frames or shear walls to a building. To demolish a building, you simply remove its post and there you go, the building collapses. Damages to most bridges in Papua New Guinea have been seen in this similitude. Flood erodes the approach embankments or scour the bridge pier and abutments and eventually sweeps away the structure. Short span bridges protruding into the waterway have been known to be easy prey than the long span bridges with intermediate pier supports on piled foundations. As the saying goes, “bridges are as good as its foundation”.

2.4.1 Types of Abutments There are different types of bridge abutments and are categorised as follows:

i. Gravity Abutment is an abutment which resists horizontal earth pressure with its own dead weight,

ii. U Abutment is a ‘U’ shaped gravity abutment, iii. Cantilever Abutment, has a cantilever retaining wall designed for large

vertical loads, iv. Full Height Abutment has a cantilever abutment that extends from the

underpass grade line to the grade line of the overpass roadway, v. Stub Abutment, is a short abutment at the top of an embankment or

slope that is usually supported on piles, vi. Semi-Stub Abutment has a size between full height and stub abutment, vii. Counterfort Abutment is similar to counterfort retaining walls, viii. Spill-through Abutment has vertical buttresses with open spaces

between them, ix. MSE (Mechanically Stabilized Earth) or Reinforced Earth Abutment

(REA) has modular units and metallic reinforcement, and x. Pile Bent abutment, are similar to Spill-through Abutment.

Any type of abutments can be satisfactorily utilised for a particular bridge site depending on its functionality and site requirements. This study is not limited to any of the abutment types, however, is undertaken to provide general abutment design guidelines to effectively resist the flooding action and its subsequent damage of the bridge abutments during designed flood return periods. Economics is usually the primary factor in selecting the type of abutment to be used in bridge construction widely. For river or stream crossings, the minimum required channel area and section are considered higher than other factors. While, highway overpasses, minimum horizontal clearances and sight distances are maintained to ensure public safety and geometric requirements of the road. These requirements mostly preside on the abutment height and horizontal spacing between the abutments and piers within the vicinity.

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An abutment built on a slope or on top of a slope is less likely to become a collision obstacle than one on the bottom of the slope and is more desirable from a safety standpoint. Aesthetics is also a factor when selecting the most suitable abutment type. The main abutment type that is often constructed for bridges in Papua New Guinea is Gravity Abutment with shallow Spread Footing Foundation and stone filled gabion baskets as retaining structure on earth-fill approach embankments. This bridge foundation is most preferred when comparing to the budget constraints, constructability issues, and availability of construction materials and engineering technology that is available in the country.

Figure 4.0. Typical components of a Bridge Abutment

Factors that contribute to the selection of abutments are: Bridge Length Bridge Skew Horizontal curves Wing-wall Presence of retaining wall Front face abutment exposure Beam depth or superstructure type, and Desired joint location.

2.4.2 Constriction Flow at Bridge Abutments Snell, Smith (2012, p.4) argued that design of bridge abutments and embankments across rivers and large watercourses located along shallow floodplains and estuaries must encompass a wide variety of design concepts. And that is to say that, selection of abutment types of bridges must not be limited to structural design only. It must consider, upstream and downstream development of the river, urbanisation effects, agricultural aspects, deforestation increasing sedimentation rates, and the climate change patterns that we face today. Thus, the multi-disciplinary studies during bridge

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investigation and design in a river crossing will help reduce the risk of the bridge to be damaged in the event of a flood. Available equations do not satisfactorily predict scour depths in bridge abutments; therefore, it is recommended that adequate abutment protection measures must be explored during the investigation and design stage. Protection measures like allowance for additional relief openings in the case of the bridge located in flood plains, construction of guide banks, river training works and installation of ripraps are some examples to minimise the adverse flow conditions at bridge abutments during the flood. Diagrams below further illustrate the channel constriction caused by bridge abutment and piers.

where: WA Width of the Abutment WB Channel width within the constricted section WP Width of the Pier WU Main Channel Width upstream of the constriction channel Lp Length of Pier

Figure 6.0 Section A - A of the constricted river channel

Figure 5.0 River Channel Flow Constriction Plan

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where: dg General scour depth dl Local scour depth dt Total scour depth df Foundation depth yu Average channel depth upstream of the constricted section

Most researchers recommend these two methods for estimating abutment scour if the abutment projects into the river channel or if the riverbank are vertical. The first method is the Pier to Abutment analogy method when assessing the flow around the projecting abutment, which is assumed that the flow around the projecting abutment is one-half of a hypothetical pier within the channel. The formula for local scour at piers is used, with an effective width, twice the length of the projecting abutment. Thus, the local scour can be estimated using the Neill Formula for well-aligned piers.

Equation 1.0 Pier Abutment analogy Method

l 1.5 p where:

Wp Pier width dl Local scour depth

This method is simple but may not be accurate as riverbank influences the flow such that the flow around the projected abutment could not be the same as flows around one-half of the pier, thus, is not be applicable if the riverbank is not vertical. Where the abutment has wing-walls, this may improve the flow past the projection, causing significantly less scouring effect than an abutment that abruptly projects into the flow. The second method is the American Federal Highway Administration (FHWA) Method. This method is used to predict the local scour at abutments on flood plains or in the main river channel. It has been developed from the laboratory data and is also of limited accuracy.

Equation 2.0 FHWA Constriction Flow Estimation Method

2.27′ .

. 1

where: a' Effective length of the abutment normal to the flow Fr Froude number k1 Abutment shape factor k2 Angle of embankment to the flow ya Flow depth at the abutment

Equation 3.0 Froude Number

√

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where: U Flow Velocity upstream of the pier g Gravitational acceleration constant (9.81m/s2) Fr Froude Number yu Average flow depth upstream of pier

Equation 4.0 Effective Length of Abutment

where: Ae Flow area affected by projected abutment ya Flow depth at the abutment

These methods may assist in giving approximate estimates for the selection and design of preferred abutment types when determining the foundation depth during preliminary design stage. Accurate estimates can then be calculated basing on sound engineering judgment when undertaking site investigation or by means of physical modelling technique if more reliable data is required.

2.4.3 Bridge Abutment on Flood Plain Interestingly, some designers prefer the use of spill-through abutments where the flood is estimated to overtop in service stage or when located in a flood plain. Thus, detail assessment and selection of abutment type and protection measures is very vital to bridges located in river or stream crossings. However, most methods used for calculating scour at abutments are notoriously inaccurate thus using engineering judgment is recommended for further assessment of the calculated results using the available equations. More improved estimates can be provided by undertaking physical modelling in accurately determining local scour at bridge abutments. This section considers the case of an abutment founded on the flood plain and set back from the riverbank. If the abutment is near to the riverbank and found on shallow foundations, a small amount of bank erosion could undermine the abutment or cause instability of the foundation. This may not be due to scour at the abutment, but to the erosion of the river channel. No formulae are available to predict the latter effect. The risk of bank erosion and undermining of an abutment, located on the flood plain, should be assessed, taking into account the stability of the river and any history of bank erosion. Appropriate bank protection measures should be provided where this type of failure is considered to be a risk. Local scour at an abutment on a flood plain is likely to be less severe than at an abutment in the main river channel. Flow velocities and depths are likely to be lower, and soils may be more resistant to erosion. Equation 2.0 of FWHA can be used, in which case the Froude number, flow depth and velocity refer to flow conditions on the flood plain rather than in the main channel. However, the method will probably overestimate local scour depths in the use of the equation. In the absence of suitable prediction methods, it is again suggested that adequate engineering judgment using specialist studies or physical modelling must be used.

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This can be concluded, that the frequent bridge abutment damages in Papua New Guinea are a proof of inadequate full-scale assessment of contributing factors affecting selection and design of bridge foundations like abutments and piers to resist the predicted flood conditions in the service life of the structure.

2.5 Bridge Pier Design Bridge Pier is a substructure unit that supports the spans of a multi-span superstructure at an intermediate location between its abutments. Wherever possible, water crossing piers should be aligned with the stream flow to avoid the creation of eddies and turbulence, which can result in scour. Two piers close to each shoreline may be more hydraulically efficient and economical to construct than one deep-water pier. Pier located near the marine environments must have the reinforcement protected from corrosion and concrete should include corrosion inhibitors. To offset abrasive action of water, bridge pier should have HPC (High-Performance Concrete) at the outer layers or form liners protection. Anerson et al, (2012) presented a technical report to the FHWA recommending that bridge foundations for new bridges should be designed to withstand the effects of scouring caused by hydraulic conditions from floods larger than the design flood. It is preferred that the pier shaft should be solid to a height of 0.9 meters above navigable elevation or 0.6 meters above 100-year flood level. Thus, affirming that the upstream face of piers should be round or ‘V’ shaped to improve hydraulics. If ice or debris is a problem, the upstream face should be battered 15 degree and armoured with steel angle to a point 0.9 meters above design high water. The wing walls on the upstream side should be aligned to flow direction of the river through the bridge opening. In the case where wing walls are at or near the water’s edge, the wing walls should be flared to improve the hydraulic entrance condition.

Figure 7.0 Types of Bridge Pier Shapes

The basic mechanism causing local scour at piers or abutments is the formation of vortices at their base. Bridge scour is the removal of sediments such as sand and rocks from around bridge abutments or piers. Scour, caused by swiftly moving water, can scoop out scour holes, compromising the integrity of a structure.

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Wikipedia (2016) published that in the United States; bridge scour is one of the three main causes of bridge failure. It has been estimated that 60% of all bridge failures result from scouring and other hydraulic-related causes. It is the most common cause of highway bridge failure in the United States where 46 of 86 major bridge failures resulted from scouring near piers from 1961 to 1976.

2.5.1 Methods for Estimating Scour at Bridge Piers Scouring at bridge piers has been a major cause of bridge failures all around the world due to the hydraulic action of the flowing stream during the flood and in clear water flow. Many researchers have undertaken considerable studies providing design guidelines, procedures and methods of scour at bridge piers and abutments. Local Scour at piers and abutments is one of the contributing factors of bridge failures in Papua New Guinea (Figure 5.0). Water normally flows faster around piers and abutments making them susceptible to local scour. At bridge openings, contraction scour can occur when water accelerates as it flows through an opening that is narrower than the channel upstream from the bridge.

Degradation scour occurs both upstream and downstream from a bridge over large areas. Over long periods of time, this can result in lowering of the streambed. Stream channel instability resulting in river erosion and changing angles-of-attack can contribute to the bridge scour. There are several equations used to determine the scour at bridge piers in bridge design. The following are the more established methods and equations.

2.5.2 General Scour General scour is the removal of riverbed material due to the constriction flow caused by the presence of pier and projecting abutment against the flow in the river channel. The simplest general scour equation is the FHWA Method, where all of the flow is contained within the riverbanks.

Figure 8.0 Local scour at bridge pier

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Equation 5.0 FHWA General Scour Estimation Method

where:

dg General scour depth WB Channel width within the constricted section WU Main Channel Width upstream of the constriction channel k1 The riverbed sediment size that is a function of shear stress and fall

velocity of the sediment. k1 values ranges from 0.59 – 0.69 yu Average channel depth upstream of the constricted section

The parameter k1 depends on the mode of sediment transport. The value of k1 ranges from 0.59 if the sediment is mostly transported as bed load, to 0.69 if the sediment is mostly transported in suspension. The value of k1 is given as a function of the shear stress on the riverbed and the fall velocity of the sediment and may be difficult to determine for real rivers. With the exception of the effect of k1, the Contraction Scour calculated from the above equation is independent of flow velocity. The depth, however, must be known, and therefore the water level should be calculated from hydraulic studies. Several approximations are made by the above approach. The formula calculates the equilibrium scour, which would occur towards the downstream end of a long contraction. In reality, it is likely that the contraction will be due to bridge abutments and piers, and will not be of sufficient length for the full depth of scouring indicated by Equation 5.0 to develop. The method neglects the effect of armouring, whereby the average bed material size increases in time due to the preferential erosion of finer material. Armoring may significantly reduce scour depths in rivers with bed sediments possessing wide grading bands. The calculated general scour depth is the average across the width of the channel. In general, scour will not be distributed uniformly across the channel width. Factors to account for this effect are given by Faraday and Charlton, who suggest that the maximum scoured flow depth can be estimated from the average scoured depth by using a scale factor. The value of the factor depends on whether the bridge crossing is located on a straight reach of the river or on a bend. Factors range from 1.25 for a straight reach to 2.0 for a right-angled abrupt turn. The location of the maximum scour will normally be towards the outside of a bend. The second method is the channel constriction with the flow over the flood plain, and abutments set back from the edge of the channel. The bridge approach embankments restrict the floodplain flow, forcing a portion of the floodplain flow back into the main channel and increasing the general scour. This implies that this case cannot be accurately analysed without knowledge of the distribution of flow between the channel and floodplain. Specialist studies may be required to establish the actual flow conditions. If the flow distribution is known, the following equation can be used to estimate general scour in the main channel beneath the bridge:

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Equation 6.0 Scouring due to constriction flow over the Floodplain

where: QmcB Main channel flow at the bridge crossing QmcU Main channel flow upstream of the bridge crossing

More interestingly, debris can also have a substantial impact on bridge scour in several ways. A build-up of material can reduce the size of the waterway under a bridge causing contraction scour in the channel. A build-up of debris on the abutment can increase the obstruction area and increase local scour. Debris can deflect the water flow, changing the angle of attack, increasing local scour. Debris might also shift the entire channel around the bridge causing increased water flow and scour in another location like bridge embankments and river banks leading into attacking the abutment.

2.5.3 Local Scour It is based on the assumption that local scour and general scour are independent, that local scour can be calculated based on hydraulic parameters which do not take account of the effect of general scour. An alternative approach is to re-calculate the hydraulic parameters such as velocity and flow depth based on the General Scour bed levels. The latter approach is more complex but could be more accurate, particularly in cases where there is significant general scour. The basic design equation for Local Scour for Well-aligned Piers by Neill (1973) is:

Equation 7.0 Local scour estimation for well-aligned piers

1.5 52.2 5

The second method is by Melville and Sutherland (1988), the basic scour depth equation 2.4Wp is modified by so many correcting factors taking into account for the pier skew as a function of the angle of flow incidence and length to width ratio of the pier. Function fu takes account of the erosion resistance of the bed, allowing for the flow velocity U, the critical velocity for the bed material Uc and armouring effects Ua. The value of fu depends on the size and grading of the bed material. If this information is not available, a conservative estimate of scouring may be obtained if a value of 1.0 is assumed for fu.

Equation 8.0 Melville and Sutherland Method

2.4 . , , . . . . ,

where: α Angle of flow incidence with respect to the pier axis d Sediment size of the streambed material

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fα Angle of flow incidence factor with respect to pier length to width ratio fd Sediment size factor fs Shape factor of the upstream pier nose fu Erosion resistance factor of the bed fy Scour reduction factor for shallow depth with respect to pier width Lp Length of pier U Flow Velocity Ua The armouring effects Uc Critical velocity for the bed material Wp Width of pier yu Average flow depth upstream of pier

Function fy is included for reducing estimates of scouring where the flow depth is shallow compared with the pier width. A conservative estimate will be obtained if fy is taken to be 1.0. This is only when the flow depth reduces to below 2.5Wp approximately, does the function fy have a significant effect in reducing estimates for local scour. Function fd is included to take account of the effects of sediment size. This factor is generally 1.0, except where the sediment size [d] is larger than yu/25. In the absence of further information, the conservative approach is to assume that fd is 1.0. Function fs take into account of the shape of the upstream nose of the pier. Rounded or streamlined bridge pier normally have less scour than the rectangular-nosed pier. The factor for a circular nose is 1.0. The function fα take into account of the angle of flow incidence and the pier length to width ratio. This was evaluated from the Neill (1973) report. The final method is the Colorado State Equation Method, which is highly recommended by the American Federal Highway Administration (FHWA). The equation basically takes into account of the Froude Number, pier nose shape factor [k1] and angle of flow incidence factor [k2].

Equation 9.0 Colorado State University (CSU) Method

. 2.0.

.

where: k1 Pier nose shape factor k2 Angle of incidence flow factor with respect to pier axis Fr Froude Number

Wp Width of pier yu Average flow depth upstream of pier

Froude Number is determined by the equation (3.0):

√

where: U Flow Velocity upstream of the pier g Gravitational acceleration constant (9.81m/s2)

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Fr Froude Number yu Average flow depth upstream of pier

These are the main available equations to estimate for the bridge scour around bridge piers.

2.5.4 Combined Scour At each bridge foundation subject to scouring action of the flowing stream, the total scour [dt] is given by the simple arithmetic equation:

Equation 10.0 Combined Scour Equation

where:

dt Total Scour depth dg General scour depth dl Local scour depth

The design bed elevation zd is calculated by subtracting the total scour dt from the natural bed elevation zo. Surveys of bed levels should be used to establish the pre-construction bed levels at the bridge site. These levels may be modified to take account of long-term aggradation or degradation to obtain the bed levels z.

Equation 11.0 Designed Bed Level Equation

Z where:

dt Total Scour depth Zd Design Bed Elevation Zo Natural Bed Elevation

Improved estimates of scour depth may be obtained if site measurements of scour are available from nearby existing bridges of similar construction to the proposed bridge, particularly if scour have been monitored during flood periods. It is recommended that bed levels and foundation levels be plotted onto several cross sections of the bridge site. General scour levels can then be adjusted to take account of its non-uniformity across the section. Local scour depths may then be superimposed on the General Scour, bed profiles.

2.5.5 Hydrodynamic Flow Pressure on Bridge Piers During the flood, the bridge pier is subject to many loads including the hydrodynamic forces induced by a flood on foundation soil, debris mat, log impact and even ice force in cold regions. This section will provide an overview of the current methods used in design when estimating loads caused by a flood on bridge piers. Hydrodynamic forces from the action of flowing water past the submerged parts of a bridge act in addition to hydrostatic forces. The Indian Road Congress (IRC) and American Association of State Highway and Transportation Officials (AASHTO) recommend the following equation for the hydrodynamic flow

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pressure [P].

Equation 12.0 Hydrodynamic Flow Pressure

0.51 where:

P Hydrodynamic Flow pressure (kN/m2) K Pier Shape Factor U Flow velocity at the point where pressure intensity is being calculated

The shape factor K is dependent upon the shape of the pier and U is the velocity of the current at the point where the pressure intensity is being calculated. The current velocity U is assumed to vary linearly from zero at the point of deepest scour to a maximum at the free water surface. The method is not suitable for cases where the current strikes the pier at an angle rather than head on, hence for these conditions the drag and lift coefficients increases rapidly with the angle of current and the hydrodynamic forces may be seriously underestimated. The following table gives the recommended values for pier shape factor. Table 3.0 AASHTO recommended Pier Shape Factor (K) Values

Pier nose shape Recommended Value (K) Square ended piers 1.5 Circular piers 0.66 Pier with triangular or angle (<30°) 0.5 Pier with cutwater or angle (30° to 60°) 0.5 to 0.7 Pier with flow angle (>60° to 90°) 0.7 to 0.9

2.5.6 Drag and Lift Forces on Bridge Pier

Apelt and Isaacs Method: A method proposed by Apelt and Isaacs has separate equations for the component of the force in the direction of flow and that normal to the flow. The component parallel to the flow is termed "drag" and that normal to the flow as “lift". Drag forces act on the pier in the direction of the flow and lift forces act upon the exposed longitudinal face, normal to the flow, in the direction of the pier centre. The equations are suitable for use for cases where the current strikes the pier at an angle as well as head on. The diagram below further describes the drag and lift force actions during flow conditions on a bridge pier. In a study undertaken in 1966, values determined from the Apelt and Isaacs equations were compared with those derived from a model study of the River Exe Bridge piers, Exeter, UK. The forces derived from the model study were found to be smaller than those derived from the Apelt and Isaacs equations that the apparent conservativeness of the equations may be due to the difference in the pier length to width ratio of the River Exe Bridge to the ratios available from the Apelt and Isaacs charts. They proposed the following equations in their study:

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Equation 13.0 Apelt and Isaacs Drag Force Equation

2000

Equation 14.0 Apelt and Isaacs Lift Force Equation

2000

where:

CD Drag coefficient CL Lift coefficient ρ Density of water (1000kg/m3)

Uo Approach flow velocity (m/s) yo Depth upstream of pier (m) L Length of pier or diameter of pier for single cylindrical pier (m)

The drag and lift coefficients for various shapes of pier and angles of approach flow are available in chart form presented in Apelt and Isaacs study. The forces are assumed to act at the mid-depth of the flow and through the pier centroid. This was confirmed by the model study undertaken for River Exe Bridge. In the case of rectangular piers, coefficients are given for piers with a length to width ratio of 6.52 only. The latter values were used, by default, for the River Exe Bridge study where the length to width ratio was 17.5.

Australian Bridge Design Standard (AS5100, 2004) The Australian Bridge Design Standard (AS5100, 2004) specifies that the bridge structures subject to water flow effects; the fluid forces on the piers are dependent on the pier shape, the water velocity and the direction of the flow. The diagram below further describes how the body of water behaves against the submerged body of the structure during a flood or in a normal flow condition.

Figure 9.0 Drag and Lift Forces on Bridge Piers

Thus the resultant drag and lift forces parallel and perpendicular respectively

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are calculated as given in the following equations.

Equation 15.0 AS5100 Ultimate Design Drag Force

0.5

Equation 16.0 AS5100 Serviceability Design Drag Force

0.5 where:

Cd Drag coefficient depending upon pier shape Vs Mean velocity of the water flow at the serviceability limit state at the level

of the superstructure or debris as appropriate Vu Mean velocity of the water flow at the ultimate limit state at the level of the

superstructure or debris as appropriate Ad Area, equal to the thickness of the pier normal to the direction of the flow,

multiplied by the height of the water flow AS5100.2 (2004) further states that in the absence of more exact estimates the values of Cd shall be assumed as follows: Table 4.0 Drag Coefficient (Cd) Value

Pier nose shape Drag Coefficient (Cd) value Semi-circular 0.7 Square 1.4 Wedge (>90°) 0.8

The Australian Bridge Design Standard (AS5100) further stipulates that the design lift forces, perpendicular to the plane containing the pier as shown in Figure 8.0 shall be calculated as per the equation given in Equations 17.0 and 18.0 for the two differently limit states respectively. In the absence of the exact estimates for the lift coefficients, the specification recommends the values provided in Table 4.0 below.

Equation 17.0 AS5100 Ultimate Design Lift Force

0.5

Equation 18.0 AS5100 Serviceability Design Lift Force

0.5 where:

CL Lift coefficient depending on the angle between the water flow direction and the plane containing the pier

Vs Mean velocity of the water flow at the serviceability limit state at the level of the superstructure or debris as appropriate

Vu Mean velocity of the water flow at the ultimate limit state at the level of the superstructure or debris as appropriate

AL Area, equal to the width of the pier parallel to the direction of the water flow, multiplied by the height of the water flow

θw Angle between the flow direction and the transverse centerline of the pier

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Table 5.0 AS5100 Lift Coefficient (CL) Values

Angle of Flow Direction (θw) Lift Coefficient (CL) Value θw ≤ 30° 0.9

θw > 30° 1.0 Thus, it is noted that in a plate or wall-type bridge piers angled to the direction of flow, transverse lift-type forces can be significant during the flood event, which requires adequate assessment during the design stage.

2.6 Bridge Foundation Design As commonly known, the foundation is the lowest load-bearing part of a structure whether it be a bridge, building, tower, lighthouse etc. Foundation supports the structure and carries all the design loads that the structure exhibits during its construction and service life. There are two main types of foundations: (a) Shallow Foundation, and (b) Deep Foundation.

Shallow Foundation The substructure with a little depth from the ground surface. Shallow foundations are preferred when there is competent soil bearing capacity or when firm bedrock is located near the foundation level. Examples are Spread and Pad Footing Foundations.

Deep Foundation The substructure of greater depth from the ground level. Most deep foundations are constructed where the soil bearing capacity is poor or where major load-carrying structures are required such as Skyscrapers and Suspension Bridges. Examples are Pile Footing and Caisson Foundations.

Figure 10.0 Typical Bridge Foundation Details

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Bridges are constructed with either of the two foundations or combination of them. The type of foundations to be constructed is determined through site investigation, geotechnical investigation and testing, river hydraulics, structure type and most of all its service requirements. These factors have been used basically in selecting the applicable foundation type of a bridge. The abutments, bridge piers, piles, footings, retaining walls and approach embankments are all part of the bridge substructure which transfers the load to the soil. Foundation selection considerations to be evaluated includes but not limited to:

The ability of the foundation type to meet performance requirements for all ultimate and serviceability limit states, given the soil or rock conditions encountered. (E.g. deformation, bearing resistance, uplift resistance, lateral resistance),

The constructability of the foundation type, The impact of the foundation installation in terms of time and space

required on traffic and right-of-way, The environmental impact of the foundation construction, The constraints that may impact the foundation installation (e.g.

overhead clearance, access, and utilities), The impact of the foundation on the performance of adjacent foundations,

structures, or utilities, considering both the design of the adjacent foundations, structures, or utilities, and the performance impact the installation of the new foundation will have on these adjacent facilities, and

The cost of the foundation, considering all of the issues listed above.

2.6.1 Hydrostatic Earth Pressures on Bridge Foundations The foundations of a bridge are particularly critical because they must support the entire weight of the bridge and the traffic loads that it will carry over its service life. Most bridges are constructed on reinforced concrete abutments acting as retaining structures on each end of the bridge superstructure with an intermediate pier support on driven-pile footing foundations or caissons. The foundation must be checked to make sure it has required the bearing capacity of the soil, the sliding resistance and the overturning stability to withstand the applied loads in its service stage. Several methods and theories are used in the design of foundation structures to cater for the hydrostatic pressure force acting on the foundation. Different theories and methods used in the design of foundation structures will be further discussed in this section. Coulomb (1776) and Rankine (1857) assumed planar failure surface and proposed methods for the estimation of earth pressure on the retaining walls. Later Terzaghi (1943) proposed a failure mechanism in which, the failure surface consisted of a log spiral originating from the wall base, followed by a tangent, which met the ground surface at an angle corresponding to Rankine’s (1857) passive state. Several research workers have adopted this mechanism. Caquot & Kerisel (1948) and Kerisel & Absi (1990) proposed a log spiral mechanism and presented their results in the form of charts. Janbu (1957), Sheilds & Tolunay (1973), Basudhar & Madhav (1980), and Kumar & Subba Rao (1997) used the method of slices for computing passive pressure coefficients in respect to cohesionless soil by considering soil mass in the state

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of limit equilibrium. Soubra & Macuh (2002) proposed a method based on rotational log-spiral failure mechanism with the upper-bound theorem of limit analysis for the computation of passive earth pressure coefficients. Lancellotta (2002) provided an analytical solution for the passive earth pressure coefficients based on the lower bound theorem of plasticity. Shiau et al., (2008) used an approach based on upper and lower bound theorems of limit analysis coupled with finite element formulation and nonlinear programming techniques for the analysis of passive earth pressures. In 2000, the American Association of State Highway and Transportation Officials (AASHTO) recommended, and the Federal Highway Administration (FHWA) concurred, that all State departments of transportation (DOTs) should follow Load and Resistance Factor Design (LRFD) principles in the design of all new highway bridges by October 2007. The AASHTO (2012) bridge specifications require the use of the load and resistance factor design (LRFD) method in the substructure design. The mathematical statement of the load and resistance factor is expressed in the equation below, which all limit states are considered of equal importance.

Equation 19.0 AASHTO LRFD Equation

Σ In this case, the load modifying factors are considered for both maximum and minimum load conditions. For loads with a higher value of load factor, the following equation is used to determine the load-modifying factor.

Equation 20.0 AASHTO LRFD maximum Load Modification Factor

0.95 For loads with a minimum value of load factor, Equation 21.0 is applicable. Equation 21.0 AASHTO LRFD minimum Load Modification Factor

11.0

where: γi Load factor is a statistically based multiplier applied to force effects ϕ Resistance factor is a statistically based multiplier applied to nominal

resistance ηi Load modifier is a factor relating to ductility, redundancy, and operational

classification ηD Factor relating to ductility ηR Factor relating to redundancy ηI Factor relating to operational classification Qi Force effect Rn Nominal resistance Rr Factored resistance (ϕRn)

Load factors are applied to loads to account for uncertainties in selecting loads

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and load effects. Performance or resistance factors are used to account for uncertainties in structural properties, soil properties, variability in workmanship, and inaccuracies in the design equations used to estimate the capacity. The ultimate limit state design suggested values of performance factors for shallow foundations and listed in the table below are values obtained from Clough and Duncan (1991) for use in the design of retaining foundation structures. Table 6.0 Performance Factors for Shallow Foundations

Type of Limit State Performance Factor

Bearing Capacity

Sand

Semi-empirical procedure (SPT)

0.45

Semi-empirical procedure (CPT)

0.55

Rational method using ϕf estimated from SPT

0.35

Rational method using ϕf estimated from CPT

0.45

Clay

Semi-empirical procedure (CPT)

0.50

Rational method using shear strength in lab test

0.60

Rational method using shear strength from field vane tests

0.60

Rational method using shear strength estimated from CPT data

0.50

Rock Semi-empirical procedure 0.60

Sliding

Precast Concrete placed on

sand

Using ϕf estimated from SPT 0.90 Using ϕf estimated from CPT 0.90

Concrete cast in place on

sand

Using ϕf estimated from SPT 0.80 Using ϕf estimated from CPT 0.80

Clay (σ<0.5P)a

Using shear strength in lab tests 0.85 Using shear strength from field vane tests

0.85

Using shear strength estimated from CPT

0.80

Clay (σ>0.5P)b Shear strength is greater than 0.5 times the normal pressure

0.85

Clough and Duncan Earth Pressure Movements (1991) During the flood event, the shear strength of the foundation soil is reduced as the water content in the soil rises. The moving load on the bridge and road surface exerts the pressure on the foundation soil, which exhibits movement on a σ<0.5P = Where shear strength is less than 0.5 times the normal pressure b σ>0.5P = Where shear strength is greater than 0.5 times the normal pressure

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the bridge foundations. Therefore, a careful study and selection of adequate fill material that can withstand excessive earth pressure during a flood are required basing on established methods and equations. Earth pressures exerted on an abutment can be classified according to the direction and the magnitude of the abutment movements. When the wall is fixed rigidly and does not move when the load is applied the pressure exerted by the soil on the wall is called at-rest earth pressure. When the foundation wall moves away from the backfill, the earth pressure decreases, which is called active earth pressure, however, when the wall moves toward the backfill, the earth pressure increases and is referred to as passive earth pressure. The experimental data and finite element analyses (Clough and Duncan, 1991), gives approximate magnitudes of wall movements required to reach minimum active and maximum passive earth pressure conditions. Table 7.0 Approximate Magnitudes of Movements required to reach the Minimum Active and Maximum Passive Earth Pressure Conditions

Type of Backfill Material Values of Δc/Hd Active Pressure Passive Pressure

Dense sand 0.001 0.01 Medium dense sand 0.002 0.02 Loose sand 0.004 0.04 Compacted silt 0.002 0.02 Compacted lean clay 0.01 0.05 Compacted fat clay 0.01 0.05

Under stress conditions close to the minimum active or maximum passive earth pressures, cohesive soils creep continually. The movements shown in the graphs below would produce active or passive only temporarily. With respect to time, the movements would continue if pressures remain constant, however, if the movements remain constant, active pressures will increase with time approaching at-rest earth pressure condition and passive pressure will decrease with time. The required movements for the extreme conditions are approximately proportional to the wall height. The movement required to reach the maximum passive pressure is about ten times as great as that required to reach the minimum active pressure for walls of the same height. The movements required to reach the extreme conditions for dense and incompressible soils is smaller than those for loose and compressible soil. The value for the earth pressure coefficient varies with wall displacement and eventually remains constant after sufficiently large displacements. The change of pressures also varies with the type of soil, that is, the pressures in the dense sand change more quickly with wall movement. c Δ = Movement of top wall to reach minimum active or maximum passive earth pressure by tilting or lateral translation d H = Height of wall

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Figure 11.0 Relationship between wall and earth pressure movement [Clough and Duncan, 1991]

Figure 12.0 Relationship between compacted backfill wall movement and earth pressure [Clough and Duncan, 1991]

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2.6.2 Methods for Estimating Active (Pa) and Passive (Pp) Earth Pressure Forces Coulomb (1776) and Rankine (1856) developed simple methods for calculating the active and passive earth pressures exerted on retaining structures. Caquot and Kerisel (1948) developed the more generally applicable log spiral theory, where the movements of walls are sufficiently large so that the shear strength of the backfill soil is fully mobilized, and where the strength properties of the backfill can be estimated with sufficient accuracy, these methods of calculation are useful for practical purposes. Coulomb’s trial wedge method can be used for irregular backfill configurations and Rankine’s theory and the log spiral analysis can be used for more regular configurations. Each of these methods will be discussed below.

Lateral earth pressure is the soil pressure that applies pressure force in the horizontal direction. The lateral earth pressure is important because it affects the consolidation behaviour and strength of the soil and because it is considered in the design of geotechnical engineering structures such as retaining walls, basements, tunnels, deep foundations and braced excavations.

The coefficient of lateral earth pressure, K, is defined as the ratio of the horizontal effective stress, σ’h, to the vertical effective stress, σ’v. The effective stress is the intergranular stress calculated by subtracting the pore pressure from the total stress as described in soil mechanics. K for a particular soil deposit is a function of the soil properties and the stress history. The minimum stable value of K is called the active earth pressure coefficient, Ka; the active earth pressure is obtained, for example, when a retaining wall moves away from the soil. The maximum stable value of K is called the passive earth pressure coefficient, Kp; the passive earth pressure would develop, for example against a vertical plough that is pushing soil horizontally. For a level ground deposit with zero lateral strain in the soil, the "at-rest" coefficient of lateral earth pressure, K0 is obtained.

Coulomb’s Theory: Coulomb (1776) first studied the problem of lateral earth pressures on retaining structures. He used limit equilibrium theory, which considers the failing soil block as a free body in order to determine the limiting horizontal earth pressure. The limiting horizontal pressures at failure in extension or compression are used to determine the Ka and Kp respectively. Since the problem is indeterminate, a number of potential failure surfaces must be analysed to identify the critical failure surface, that is, the surface that produces the maximum or minimum thrust on the wall. Mayniel (1908) later extended Coulomb's equations to account for wall friction, symbolised by δ to account for the friction angle. Müller-Breslau (1906) further generalised Mayniel's equations for a non-horizontal backfill and a non-vertical soil-wall interface represented by angle θ from the horizontal. Hence, Coulomb’s theory was further developed and was named after him. The coulomb theory, the first rational solution to the earth pressure problem, is based on the concept that the lateral force exerted on a wall by the backfill can be evaluated by analysis of the equilibrium of a wedge-shaped mass of soil

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bounded by the back of the wall, the backfill surface, and a surface of sliding through the soil. The assumptions in this analysis are:

a) The surface of sliding through the soil is a straight line, and b) The full strength of the soil is mobilised to resist sliding shear failure

through the soil.

1. Active Pressure Force (Pa) The active pressure in Coulomb’s Theory can be expressed as a function of the height of backfill along the failure plane as shown in Figure 13.0 below. Thus the active earth pressure equation is derived from this theory in which

Figure 13.0 Coulomb Active Earth Pressure Force

Equation 22.0 Coulomb Active Earth Pressure Force (Pa)

12

Ka is a coefficient of active earth pressure along the failure plane. Therefore, Ka is expressed mathematically as follows:

Equation 23.0 Active Earth Pressure Coefficient (Ka)

cos 1sin sin cos cos

Therefore, the Active Earth Pressure Equation is now expressed finally in this form.

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Equation 24.0 Coulomb’s Active Earth Pressure Equation

12


where: Pa Active Earth Pressure Force (kN/m) Pp Passive Earth Pressure (kN/m) Ka Coefficient of active earth pressure γ Unit weight of backfill soil material (kN/m3) H Wall height (m) ϕf Internal friction angle of soil (degrees) β Slope of the stem face (degrees) δ The friction angle between wall and soil (degrees) i Slope of backfill surface (degrees)

2. Passive Earth Pressure

The coulomb theory can be used to evaluate passive earth resistance, using the same basic assumptions. Figure 14.0 shows the failure mechanism for the passive case. The passive earth pressure force, [Pp] is expressed in the following equation basing on the figure below.

Equation 25.0 Coulomb Passive Earth Pressure Force (Pp)

12


Figure 14.0 Coulomb Passive Earth Pressure Force

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The basic assumption in the coulomb theory is that the surface of sliding is a plane. This assumption does not affect appreciably the accuracy for the active case. However, for the passive case, values of Pp calculated by the coulomb theory can be much larger than can actually be mobilised, especially when the value of δ exceeds about one-half of ϕf. In this case, Rankine’s Theory uses the friction angle behind the foundation wall to determine the earth pressures against the wall.

Rankine’s Theory: Rankine's Theory assumes that failure will occur when the maximum principal stress at any point reaches a value equal to the tensile stress in a simple tension specimen at failure. This theory does not take into account the effect of the other two principal stresses, yet is satisfactory for brittle materials, and is not applicable to ductile materials. This theory is also called the Maximum Stress Theory and assumes a frictionless soil-wall interface and a vertical wall with no wall slope, which considers the soil to be in a state of plastic equilibrium and makes the assumptions that the soil is homogeneous, isotropic and has internal friction. The pressure exerted by soil against the wall is referred to as active pressure. The resistance offered by the soil to an object pushing against it is referred to as passive pressure thus; Rankine's theory is applicable to incompressible soils. Friction between the wall and backfill has an important effect on the magnitude of earth pressures and an even more important effect on the direction of the earth pressure force. The Rankine theory is applicable to conditions where the wall friction angle (ϕ) is equal to the slope of the backfill surface (I). As in the case of the coulomb theory, it is assumed that the strength of the soil is fully mobilised. The table below presents the values of the maximum possible wall friction angle (δ) for various wall materials and soil types from United States Department of Navy (1982). Table 8.0 Ultimate Friction Angles US Department of Navy (1982)

Interface Materials (Soil Type) Friction Angle (δ) in degrees

Mass concrete on the following

foundation materials

Clean sound rock 35 Clean gravel, gravel-sand mixtures, coarse sand

29-31

Clean fine to medium sand, silty medium to coarse sand and silty or clayey gravel

24-29

Clean fine sand, silty or clayey fine to medium sand

19-24

Fine sandy silt, non-plastic silt 17-19 Very stiff and hard residual or pre-consolidated clay

22-26

Medium stiff and stiff clay and silty clay 17-19 Masonry on foundation

materials has

Steel sheet piles against the following soils:

Clean sand, gravel-sand mixtures, well- 22

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same friction factors

graded rock fill with spalls Clean sand, silty sand gravel mixture, single-size hard rock fill

17

Silty sand, gravel or sand mixed with silt or clay

14

Fine sandy silt, non-plastic silt 11

Formed precast concrete or

concrete sheet piling against the

following soils

Clean gravel, gravel-sand mixture, well-graded rock fill with spalls

22-26

Clean sand, silty sand-gravel mixture, single-sized hard rock fill

17-22

Silty sand, gravel or sand mixed with silt or clay

17

Fine sandy silt, non-plastic silt 14

Various structural materials

Masonry on igneous and metamorphic rocks:

Dressed soft rock on dressed soft rock 35 Dressed hard rock on dressed soft rock 33 Dressed hard rock on dressed hard rock

29

Masonry on wood in direction of gross grain

26

Steel on steel at sheet pile interlocks 17

1. Rankine’s Active Earth Pressure The active earth pressure considered in the Rankine theory is illustrated in Figure 15.0 (a) for a levelled backfill condition. The Active Earth Pressure Force is calculated using the following equation.

Equation 26.0 Rankine Active Earth Pressure Force (Pa)

The coefficient of active earth pressure, Ka, can be expressed in the following equation as:

Equation 27.0 Rankine' Active Earth Pressure Coefficient (Ka)

cos

where: Pa Active Earth Pressure Force (kN/m2) Pp Passive Earth Pressure (kN/m2) Ka Coefficient of active earth pressure Kp Coefficient of Passive Earth Pressure γ Unit weight of backfill soil material (kN/m3) h Wall height (m)

ϕf Internal friction angle of soil (degrees) β Angle that the soil top surface makes with horizontal (degrees) δ The friction angle between wall and soil (degrees) c Cohesion Pressure Force (kN/m2)

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The variation of active pressure with depth is linear, as shown in figure 15.0 (b). If the backfill is cohesive, the soil is theoretically in a tension zone down to a depth of .

However, a tension crack is likely to develop in that zone and may be filled with water, so that hydrostatic pressure will be exerted on the wall, as shown in figure 15.0.(c).

2. Rankine’s Passive Earth Pressure Force The Rankine theory can also be applied to passive pressure conditions. The passive earth pressure coefficient (Kp) can be expressed as:

which, can be expanded in this form below

Equation 28.0 Rankine Passive Earth Pressure Coefficient (Kp)

coscos

cos √

Therefore, the Rankine’s Passive Earth Pressure Force is better expressed as:

Equation 29.0 Rankine Passive Earth Pressure Force (Pp)

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Figure 15.0 Rankine's Theory for Active Earth Pressure in a Frictionless Wall

Caquot and Kerisel Theory: Albert Caquot and Jean Kerisel (1948) developed an advanced theory that modified Muller-Breslau's equations or better known as Coulomb-wedge Theory of Active and Passive Earth Pressure Forces to account for a non-planar rupture surface. They used a logarithmic spiral to represent the rupture surface instead. This modification is extremely important for passive earth pressure where there is soil-wall friction. Mayniel and Muller-Breslau's equations are un-conservative in this situation and are dangerous to apply. For the active pressure coefficient, the logarithmic spiral rupture surface provides a negligible difference compared to Muller-Breslau. These equations are too complex to use, so tables or computer software are used instead to determine the earth pressure forces.

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Active and passive pressure coefficients Ka and Kp obtained from analysis using log spiral surfaces are listed in Figures 18.0 and 19.0 (Caquot and Kerisel, 1948). Values of Ka and Kp for walls with level backfill and vertical stem are also shown in Figure 17.0. These values are also based on the log spiral analyses performed by Caquot and Kerisel. A log spiral more closely approximates the failure surface in most cases than a straight line using the Coulomb wedge theory, as shown in figure 16.0 below.

Figure 16.0 Caquot and Kerisel Log Spiral Failure Surface

Selecting a proper earth pressure coefficient is essential for successful wall design. A number of methods previously discussed can be used to decide the magnitude of the coefficients. A decision on what type of earth pressure coefficient should be used is based on the direction and the magnitude of the wall movement.

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Figure 17.0 Active and Passive Pressure Coefficients for Vertical Wall and Horizontal Backfill based on Log Spiral Failure Surfaces

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Figure 18.0 Caquot and Kerisel Active Pressure Coefficient (Ka) Values for Log Spiral Failure Surfaces

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Figure 19.0 Caquot and Kerisel Passive Pressure Coefficient (Kp) Values for Log Spiral Failure Surfaces

Based on the geotechnical site investigation reports and preliminary design calculations, use which method that is applicable to the failure cases and determine the hydrostatic active and passive pressure force for the bridge foundation. These methods have certain limitations and it is advisable to use applicable computer software to determine the pressure to ascertain the values from the suggested methods.

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2.7 Design of Flow Hydrology is a branch of science that deals with water, related to its properties and distribution in the atmosphere, on the land surface and beneath the earth’s surface. Adequate knowledge and understanding of this field assist bridge designers and builders to build flood resistant structures. Poor application of it often results in its disadvantage that can lead to the subject of this study. In addition, the field of bridge engineering that mainly deals with the mechanics of fluid especially water during bridge design is known as hydraulics. One’s bridge over a natural stream crossing is as strong as the better design of its hydraulics; the better assessment and design saves the bridge from being affected by the estimated storm or flood event. Zevenbergen et al (2012, p.4) reported that hydraulic issues remain a leading factor in bridge failures in many parts of the world. American Federal Highway Administration recognised that these activities need to include efforts to better collect, understand and deploy more recent and robust guidance and techniques to the accepted state of hydraulic and waterway related practices.

2.7.1 Introduction It gives us more evidence that bridge failures due to hydraulic effects and its related causes require detail investigation, study and development of more rigorous oversight of bridge failures due to flood. Many significant aspects of bridge hydraulic design that will be explored in this study include, flood estimation, design discharges, overtopping, bridge design impacts on scour and stream instability, and sediment transportation. The impacts of bridge design and construction on the highways, safety to the travelling public, and the natural environment can be significant. An economically viable and safe bridge is one that is properly sized, designed, constructed, and maintained. The structure at most must withstand the design flood in the serviceability limit state and able to accommodate overtopping with no or less structural damage in the ultimate limit design state. In general, although longer bridges are more expensive to design and build than shorter bridges, they cause fewer backwater issues, experience less scouring, and can reduce impacts to the environment. Increased scour from too short a bridge requires deeper foundations and necessitate countermeasures to resist these effects that lead to higher maintenance costs during service life. A properly designed bridge is one that balances the cost of the bridge with concerns of safety to the travelling public, impacts to the environment, and regulatory requirements that do not cause harm to those that live or work in the floodplain upstream and downstream of the bridge. Thus, it reduces maintenance cost and withstands major design flood events. Richardson et al, (2001, p.11) also stated that bridge design engineers, and those involved in transportation, navigation, and flood control often mistakenly consider a natural river to be static; that is to say, unchanging in shape, dimensions, and pattern. However, natural alluvial river generally continuous to

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change its position and shape as a consequence of hydraulic forces acting on its bed and banks or river channel during normal and flood flows. These effects of different flow characteristics of the river increase the risks of streambed erosion and channel diversion which eventually affects the bridge foundations such as, abutments, piers and embankments. Therefore, this section will present flood estimation methods for flood resistant bridge design in Papua New Guinea.

2.7.2 Flood Design and Estimation Mannings's Equation One of the most commonly used equations governing Open Channel Flow is known as the Mannings’s Equation. It was introduced by the Irish Engineer Robert Manning in 1889 as an alternative to the Chezy Equation. The Mannings equation is an empirical equation that applies to uniform flow in open channels and is a function of the channel velocity, flow area and channel slope. Under the assumption of uniform flow conditions the bottom slope is the same as the slope of the energy grade line and the water surface slope. The Manning’s “n’’ is a coefficient which represents the roughness or friction applied to the flow by the channel. Mannings’s n-values are often selected from tables, but can be back calculated from field measurements. In many flow conditions the selection of a Manning’s roughness coefficient can greatly affect computational results. The equation can be used to determine the flow velocity of the channel

Equation 30.0 Mannings’s Equation for Open Channel Flow

1∗ ∗ √

where: Q Flow rate (m3/s) V Flow velocity (m/s) A Flow area (m2) n Mannings Roughness Coefficient R Hydraulic Radius (m) S Channel Slope

Papua New Guinea Flood Estimation Manual The Papua New Guinea Flood Estimation Manual (1990) provide a standard guidelines for the estimation of floods in Papua New Guinea. This manual is intended for general use in the planning and design of small to medium sized engineering works in particular for the planning and design of bridges, culverts, small dams, drainage works and flood mitigation works in the country. Therefore, this section will present the various design methods and procedures from this manual and select the applicable methods for this study and its related works. However, the manual has limitations as the methods cannot be used for large engineering works such as large dams, major bridges or extensive flood

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mitigation works. The manual recommends special investigation by hydrologist for specialist advice and assessment. It covers the design of works to 100-year ARI (Annual Recurrence Interval) or referred to as “Return Period” in the manual. The procedures in the manual provides for “best estimates” of flood, as such as there is no factor of safety to allow of inaccuracies as in the case of other flood estimation manual. The procedures and methods in the manual are primarily directed to the estimation of design peak flood discharges, yet provide for the complete estimation of hydrographs for the design floods. The various flood estimation methods used in Papua New Guinea for flood design presented in Papua New Guinea Flood Estimation Manual (1990) are:

Regional Flood Frequency Method Local Flood-level Data Analysis Local or Nearby Flood Discharge Data Analysis Regional Flood Hydrograph Shape Estimation Method Rational Method Runoff Routing Method Computation of Design Water Levels Flood Estimation in Urban Catchments, and Estimation of Large and Extreme Floods.

The selection of the appropriate flood estimation method for a specific situation depends on the number factors including:

a) Type of data required. Whether a design peak discharge is sufficient or a complete design hydrograph is required

b) Availability of flood data on the same river or nearby similar catchment c) Locality of the catchment, either is rural or urban d) Abnormal characteristics of the catchment such as swamp or karst e) The catchment size or area, and f) The importance or type of works (e.g. Bridge, Culvert or Dam).

Thus, with the selection criteria of applicable flood design estimation methods given above, and in conjunction with the scope of this study, three flood design methods from this manual are applicable for this study and hence will be explored in detail. The three methods listed below are mostly recommended for use in flood design of bridges in Papua New Guinea and they are:

1) Regional Flood Frequency Method 2) Rational Method, and 3) Estimation of Large and Extreme Floods; which is specialized procedure

for works not catered by other methods and the return period is more than 100 years.

2.7.3 Regional Flood Frequency Method This method is used for design of works in rural catchments for the design period up to 100 years and is based on regression analysis sixty-six flood records with various catchment parameters. The assessed catchments were located throughout Papua New Guinea and contain catchment areas ranging

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from 5km2 to 40, 900km2. The method is used in conjunction with Regional Flood Hydrograph Shape Estimation Method or the Runoff Routing Method and is applicable when the flood estimation works fulfill the following requirements:

For rural catchments Catchment areas of 4km2 and greater Return periods up to 100 years When design peak discharges are required, and When design flood hydrographs are required in conjunction with other

methods mention in the paragraph above. The method uses six input catchment parameters for the flood design estimation and they are:

a) Catchment Area (km2) obtained from the topographic maps b) P2-The Daily Rainfall Intensity (mm) from the rainfall intensity maps

attached in Appendix G c) The Slope Index of the main channel (m/km) d) 1.0 + decimal proportion of swamp or flood-prone land along the main

river channel as defined on the 1:100 000 topographic maps e) Catchment Shape Index, and f) Percentage of Karstic Land in the catchment in the 1:100 000

topographic maps. The Flood Design Estimation Procedure

1) Determine the values of the catchment input parameters described above

a. Catchment Area (km2) b. P2 (mm) c. Slope (m/km) d. Swamp adjustment factor e. Shape index f. Karst (%)

2) Compute the “Swamp adjustment factor” KS 3) Check that the combinations of the variables Areas, P2 and Slope are

within the limits used for the procedure. If the combinations are not consistent then use the alternative regression equations to determine Q2 and Q100.

4) Determine the 2-year (Q2) return period peak flood estimate using the following equation:

Equation 31.0 Two Year Return Period (Q2) Peak Flood Estimate

0.028 ∗ . ∗ . ∗ If P2 is outside the limits then use the alternate regression Equation 32.0 given below.

Equation 32.0 Alternate Two Year Return Period (Q2) Peak Flood Estimate

4.0 ∗ . ∗

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5) Compute the 100-year return period peak flood estimate

Equation 33.0 100-Year Return Period (Q100) Peak Flood Estimate

0.059 ∗ . ∗ . ∗ . ∗ If the combinations are outside the limits then use the alternate regression Equation 34 if slope only is outside of the limits and Equation 35 if both P2 and slope are outside of the limits. Equation 34.0 Alternate Q100 Return Period if Slope only is outside the limits

0.095 ∗ . ∗ .

Equation 35.0 Alternate Q100 Return Period if both P2 and Slope are outside the limits

13.4 ∗ .

6) Determine the flood discharges of other return periods (QT).

Equation 36.0 Flood Discharges of other return periods (QT)

where: KQ5 = 0.27 KQ10 = 0.45 KQ20 = 0.62 KQ25 = 0.67 KQ50 = 0.83

7) Other return periods (T) the value of QT maybe determined by graphical interpolation of the estimates calculated in Step 6. Use of Gumbel Probability paper in Appendix H is recommended for this purpose.

8) For catchments located in regions subjected to heavy rainfall during the south-east season or the regions of Milne Bay and North Solomon Provinces in Papua New Guinea which are affected by tropical cyclones, it is recommended that design discharge estimates be increased by an arbitrary 50%.

This flood estimation method is subjected to certain independent factors for its accuracy such as, the accuracy and representation of basic flood data used in deriving the procedure, the accuracy of the flood frequency analysis of each flood record used, the accuracy of the derived regression equations, the representativeness of the catchments used in the study and those catchments to be applied by this procedure. For catchments which do not satisfy these conditions, the range of standard errors can be increased and that they must conform to the following criteria:

Combinations of AREA, P2 ad SLOPE are outside the derivation range Occurrence of Karst is greater than 10% Occurrence of Swamp is greater than 1.05

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Occurrence of Shape is greater than 5.0, and The location of the catchment is located in a region subjected to heavy

rainfall due to tropical cyclones.

2.7.4 Rational Method This method is used for design of works in rural catchment areas less than 4km2 for the design return period up to 100 years. The procedure was derived from measured flood data on thirty streams with catchment areas ranging from 5km2 to 350km2 in Papua New Guinea. The method is used when design peak discharges are required and is more suitable than the Regional Flood Frequency Method for catchments less than 4km2, (SMEC, 1990). This method uses the following equation to determine peak design of the channel.

Equation 37.0 Rational Flood Design Method

∗ , ∗3.6

where: QT Is the peak design discharge (m3/s) for the return period, T (years) CT Is the runoff coefficient for return period, T IT,tc Is the point of rainfall intensity (mm/h) of duration, tc (hours) of

return period, T A Is the catchment area (km2)

Flood Design Estimation Procedure This method uses the following procedure to determine the peak design discharge of the required return period (T).

1) Measure the following physical parameters from the topographic maps Catchment Area (km2), Length of main channel (km) Slope Index of main channel (% and m/km) Mean Catchment Elevation (m above sea level), and P2 – Daily Rainfall Intensity index (mm).

2) Determine the time of concentration (tc, hours) for the catchment using the Ramser-Kirpich Formula in Equation 38.0.

Equation 38.0 Ramser-Kirpich Formula

0.387√

.

where: L Is the main stream length (km) S Slope index (%) tc Time of Concentration (hours)

3) Derive the point rainfall intensity (IT, tc) for the catchment for the required return period (T) and duration (tc).

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4) Using the P2 values extracted in Step 3 and Width (Width = Area/Length), compute the runoff coefficient (C2) from Equation 39.0. In all cases adopt C2 minimum value of 0.10 and maximum of 0.40.

Equation 39.0 Runoff Coefficient (C2)

0.39 0.0006 0.036 ln 0.03 ln where:

ln Is the natural logarithm (loge) S Slope index (m/km) Elevation Height above the sea level (m) Width Width of main channel (km) which can be calculated as

(Area/Length)

5) Determine the value of CT for the required return period (T) by extracting the ratio, CT/C2.

6) Finally, calculate the design peak discharge using Equation 37.0

2.7.5 Estimation of Large and Extreme Floods The Papua New Guinea Flood Estimation Manual (SMEC 1990) do not provide standard guidelines and procedures on how to estimate the design discharge for the extreme flood conditions. However, recommends that a specialist investigation and assessment is required in this case. The design floods with a return period exceeding 100 years was beyond the scope of the manual. This type of design floods generally, with return periods beyond 100 years will require the estimation of the Probable Maximum Flood (PMF) which is termed as the maximum flood that is expected to occur in the service life of the bridge. PMF does not have a have a fixed return period associated with it but it is considered to be equivalent to a flood with a return period ranging from 10, 000 years to 10,000,000 years. For design of major bridges, most times estimation of design peak discharges greater 100 years and less than the PMF is sometimes required such as return periods between Q200 to Q2000. This can be estimated by application of a design storm of the assigned return period (e.g. Q1000) to the unit hydrograph or runoff routing model, and even it can be estimated by interpolating 100-year return period (Q100) and the PMF alternatively. The PMF is the largest flood that could conceivably occur at a particular location, usually estimated from probable maximum precipitation, and where applicable, snow melt, coupled with the worst flood producing catchment conditions. Generally, it is not physically or economically possible to provide complete protection against this event. The PMF defines the extent of flood prone land, that is, the floodplain. The extent, nature and potential consequences of flooding associated with a range of events rarer than the flood used for designing mitigation works and controlling development, up to and including the PMF event should be addressed in a floodplain risk management study.

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Estimates of PMF are based on corresponding estimates of Probable Maximum Precipitation (PMP) on the catchment and converted to PMF using a unit hydrograph of routing model which are calibrated for recorded floods. The estimation of PMP is a highly specialized task and should be carried out by and experienced meteorologist who has experience in such works. For Papua New Guinea, the Papua New Guinea Flood Estimation Manual (SMEC 1990) recommends that, the designers must consult the Papua New Guinea National Weather Service and if necessary consult Australian Bureau of Meteorology to prepare the PMP estimates.

2.8 Design for Structural Stability Design for structural stability is the real essence of bridge design. Any structure designed for use in anyway, such as sports stadium, hotel apartments, communication towers, electricity poles or a simple family house must be able to withstand all types of loads. Thus, the design engineer responsible for the design must make sure all possible forces expected to be applied in limit or ultimate state must be properly estimated and correctly accounted for during design. In flood resistant bridge design, design for structural stability is observed on bridge superstructure loads on substructure, foundation design for abutments and footings and bank protection structures.

2.8.1 Design for Structural Adequacy In the design of bridge superstructure for flood resistant, the structural stability checks must be carried out on the deck and girder or beam connections to the abutments and piers due to uplift force from the flood. The superstructure must be able to withstand the 100-year flood and able to submerged under 2000-year flood with no or less structural damage. The design is made sure to meet all the required design criteria in accordance to the bridge design standards of the relevant government bodies. In the context of Papua New Guinea, the design must conform to Australian Bridge Design Specification (AS5100) and other relevant standards such as PNG Flood Estimation Manual and Department of Works Roads & Bridges Specification June 2015.

2.8.2 Design for Foundation Adequacy It is the role of the design engineer to determine the total potential scour depth of the bridge and that the foundation footings of the pier and abutment are located below the total scour depth. The foundation must be designed to perform in service even if the scour reaches the total scour depth level. Hence, it must meet both the serviceability and ultimate limit state conditions in the unlikely event of flood as the bridge is subject to flood and water forces. The design engineer must be able to consult with a specialist hydraulics engineer in undertaking the design of bridge to resist flood. Other, stakeholders and government bodies must be consulted to make sure all design requirements are met. Section 2.6 of this chapter provides some adequate foundation design methods.

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2.8.3 Design for Flood Protection Structures In order for the bridge to sustain in itself in the major flood events, the design engineer must design and incorporate appropriate flood protection structures during the design stage. Many times the design engineer neglects the inclusion of these structures, which often leads to structure being exposed to flood attack and damage. Some of the appropriate bank protection structures that protect the bridge are mentioned in Section 2.11 of this chapter. The design engineer must study the river flow characteristics, its geomorphology, surrounding river environment upstream and downstream of the bridge and design the structure that is able to assist the structure to perform in service. The flood protection structures are structures that are constructed along the riverbank like ripraps or sheet piles that control and prevent flood and flow energy of water in directly attacking the bridge substructure or the like. Most natural rivers have a non-predictable flood pattern with non-uniform flow conditions during flood. Therefore, it is most advisable to undertake a holistic flood assessment during investigation and design stage to enable flood resistant bridge design that is adequate to cater for the flood. This is the primary purpose of the study as many bridges in Papua New Guinea have failed due to lack of appropriate design methods not incorporated in the design of river bridges which have succumbed to flood.

2.9 Design of Afflux in Bridges Afflux at bridges and culverts can be a significant source of flood risk by causing elevated flood water levels. Wide ranges of methods are currently used to model afflux, but a review of current practice found that these are not always well understood and can be applied inappropriately (Pepper). Some of the underlying assumptions and calibration data are not the most relevant for typical situations in Papua New Guinea. Therefore this section will provide some studies and accepted design methods in the design of afflux in bridges.

2.9.1 What is Afflux? Afflux is the rise in water level above normal water depth on the upstream side of a bridge or culvert caused when the effective flow area of the obstruction is less than the natural width of the stream immediately upstream of the structure. The afflux as illustrated in Figure 20 is for a bridge structure located in a watercourse. The dashed line represents the normal water surface for the undisturbed watercourse. The solid line represents the water surface when the structure is present. Afflux is shown as the maximum increase of water level above normal depth in the undisturbed stream. Note that the afflux differs from the headloss across the structure, as the latter varies depending on the upstream and downstream locations of measurement. When a structure such as a bridge or a culvert is placed in a stream, there is a local loss of stream energy. This is due to the fluid friction in contact with the structure, and the stagnation zones that border the contracting (Sections 4 to 3) and expanding (Sections 2 to 1) flow reaches. To maintain a steady flow, this local loss of energy is compensated by an increase in potential energy

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immediately upstream of the structure. A backwater is thus created which begins at the afflux location.

Figure 20.0 Side Elevation at a Bridge Contraction

2.9.2 Importance of Afflux in Bridge Design Elevated water levels upstream of bridges and culverts are a potential source of flood risk. In general, the afflux increases with increasing flow rates and with an increasing degree of obstruction, which may be related to the size and form of the structure or to transient debris blockage. Whilst bridges and culverts can be located anywhere, they tend to be concentrated in urban areas, and so the consequences of even quite small increases in the level above a threshold may be severe in terms of property flooding or disruption of infrastructure.

The effects of bridges and culverts on flood water levels need to be understood for design, planning, hydraulic modelling including models used for flood mapping and risk analysis, maintenance and incident management. The hydraulics of bridges and culverts are complex, and not all applications justify a costly, detailed analysis. But what methods should be used for analysis or modelling for the design of bridges is paramount in order to withstand the designed flood level.

2.9.3 Afflux Estimation Methods There are several afflux estimation methods used by different state organisations in estimating afflux in bridges. Presented in this paper are some commonly used methods accepted widely. Most designers today use design software and flood modelling techniques in accurately estimating afflux of bridges. USBR Bureau of Public Roads (USBPR) Method This method is widely used and is suitable for bridges with flat decks as opposed to arch bridges. In the absence of any flow bypassing the bridge site, the afflux caused by the bridge is given by the following equation.

Equation 40.0 USBPR Method

∆

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In general, if the flow velocity is U, then the velocity head H is defined as,

Equation 41.0 Velocity Head

2

where: Href Is the reference velocity head Hu Is the velocity head upstream of the structure Hd Is the velocity head downstream of the structure U Is the flow velocity H Is the velocity head g k

Is the gravitational force Is the overall backwater coefficient

Eccentricity is important if the width of the floodplain, on one side of the river, is more than about six (6) times the width of the floodplain on the other side of the river. The effects of any skew of the floodplain crossing depends on the angle that the embankment makes with the general direction of floodplain flow and the alignment of the ends of the flood embankments to that flow direction. The principal effects of the geometry of the site are contained in the overall backwater coefficient k. The USBPR manual defines k by the following equation.

Equation 42.0 Backwater Coefficient (k)

∆ ∆ ∆ where:

Kb Base coefficient, which depends on the magnitude of the constriction of the floodplain flow by embankments on either side of the bridge.

Δkp Pier coefficient which depends on the proportion of the river channel blocked by piers and also their shape

Δke Eccentricity of the floodplain crossing Δks Skew of the floodplain crossing

2.9.4 Afflux at Arch Bridges Methods have been recently developed specifically for estimating afflux at arch bridges. Single span and multi-span arch bridges and other bridge types were investigated, using model experiments and field data. These studies were limited in respect of the upstream channel being of essentially uniform depth and velocity distribution. Based on this work, an empirical method has been derived for determining the afflux at single or multi-span arch bridges. The data required are the bridge geometry, water depth and flow velocity downstream of the bridge. The same method applies to single and multi-span arch bridges provided that the multi-span arch bridges can be considered to be essentially a single, uniform, unit separated only by typical pier widths. The method is not designed for application to multi-span arch bridges with different soffit heights or arches on floodplains, and only a limited range of arch shapes was tested in the laboratory. HR Wallingford, 1988, undertook an investigation and research in determining

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methods used in estimation of Afflux at Arch Bridges. The report determined that the afflux calculation methods used for flat-deck bridges were proved inappropriate for bridges with arch soffits. In this study 192 bridges causing afflux problems in Britain where investigated as it emphasized the need for a better method of afflux prediction. The theoretical method adopted in this research followed an analogical method suggested by Raga Raju (1983) in his research for Rational Assessment of Blockage Effects in Channel Flow past Smooth Cylinders. This theory is based on the principle that afflux and related energy loss are dependent on the drag characteristics of the cylinders. The study developed the two basic principle iterative equations in determining afflux at Arch Bridges. Equation 43.0 Method of Estimating Afflux depth at Upstream of Arch Bridge

∆3

∆2

∆2

∆ [ ]∆

10

Equation 44.0 Method of Estimating Afflux depth at Downstream of Arch Bridge

∆3

∆2

∆2

∆ [ ]∆

10

where: ∆h Afflux term (D1-D2) is the difference between upstream and downstream

water levels measured away from the immediate influence of the bridge D1 Upstream depth of flow D2 Downstream depth of flow D3 Mean depth of flow measured where mean velocity is V3 Fr3 Froude Number measured at depth D3 where mean velocity is V3 J1 Upstream blockage ratio (area of blockage of bridge at depth D1/area of

flow) J3 Downstream blockage ratio (area of blockage of bridge at depth D2/area of

flow) Cd Drag Coefficient (Fd/0.5ρ(V)2*J*B*D)

0.5ρ(V)2 = kinetic energy of flow J*B*D = blockage area of bridge at the particular flow depth

Therefore, this empirical methods can be used in determining the afflux at single and multiple arch bridges. The data required in this basic methods are bridge geometry, water depth at different locations upstream and downstream and Froude Number, which can be calculated from Equation 3.0. The accuracy of the results in these empirical methods is +10 percent (HR Wallingford, 1988). Results are presented in terms of upstream and downstream blockage ratios. Thus, in terms of accuracy, there is no clear cut advantage in the use of one rather than the other. However, use of upstream blockage ratio requires an iterative procedure, whereas use of downstream blockage ratio enables afflux to be obtained in a single step. Therefore, the later method is preferred over the other for application.

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The same method applies to single and multiple arch bridges, provided that the multiple arches are single units’ separated by pier widths. The influence of eccentricity in these methods over the bridge and river channel is insignificant relative to the overall tolerance on the calculation of afflux.

2.10 Bridge Scour and Countermeasures

2.10.1 Introduction Scour and stream instability problems have always threatened the safety of our nation's highway bridges. Countermeasures for these problems are defined as measures incorporated into a highway-stream crossing system to monitor, control, inhibit, change, delay, or minimise stream instability and bridge scour problems. A plan of action, which can include timely installation of stream instability and scour countermeasures, must be developed for each scours critical bridge. Monitoring structures during and or after flood events as a part of a plan of action can also be considered an appropriate countermeasure. Numerous measures are available to counteract the actions of humans and nature, which contribute to the instability of alluvial streams. These include measures installed in or near the stream to protect highways and bridges by stabilising a local reach of the stream, and measures, which can be incorporated into the highway design to ensure the structural integrity of the highway in an unstable stream environment. Countermeasures include river-stabilizing works over a reach of the river up- and downstream of the crossing. Countermeasures may be installed at the time of highway construction or retrofitted to resolve scour and instability problems as they develop at existing crossings. The selection, location, and design of countermeasures are dependent on hydraulic and geomorphic factors that contribute to stream instability, as well as costs and construction and maintenance considerations.

2.10.2 Countermeasure Planning and Design While considerable research has been dedicated to designing of countermeasures for scour and stream instability, many countermeasures have evolved through a trial and error process. In addition, some countermeasures have been applied successfully in one local, state, region or country, but have failed when installations were attempted under different geomorphic or hydraulic conditions in other localities. In some cases, a countermeasure that has been used with success in one province or region is virtually unknown to highway design and maintenance personnel in another province or region. Thus, there is a significant need for information transfer regarding stream instability and bridge scour countermeasure design, installation, and maintenance. Since bridge scour evaluation requires multidisciplinary inputs, it is often advisable for the hydraulic engineer to involve structural and geotechnical engineers at this stage of the analysis. Once the total scour prism is plotted,

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then all three disciplines must be involved to determine the structural stability of the bridge foundation. For a new bridge design, if the structure is stable the design process can proceed to consideration of environmental impacts, cost, constructability, and maintainability or if the bridge is unstable, revise the design and repeat the analysis. For an existing bridge, a finding of structural stability at this stage will result in a low risk evaluation, with no further action required. However, a Plan of Action must be developed for an unstable existing bridge with scouring critical to correct the problem as outlined in the flow chart below summarised from FHWA Hydraulic Circular No. 23, 2009. The detail of the flow diagram is attached in Appendix E of this document.

Figure 21.0 Flow Chart for Scour and Stream Stability analysis and evaluation

The scour problem may be so serious that installing countermeasures would not provide a viable solution and a replacement or substantial bridge rehabilitation would be required. If countermeasures would correct the watercourse instability or scour problem at a reasonable cost and with acceptable environmental impacts, the analysis would progress to Step 3 of the flowchart. FHWA Hydraulic Engineering Circular 23 provides a range of resources to support bridge scour and stream instability countermeasure selection and design. A countermeasure matrix presented in the circular has a variety of countermeasures that have been used to control scour and stream instability at bridges.

Str

ea

m S

tab

ility

an

d G

eom

orp

hic

As

ses

sm

en

t

•Data Collection & Site Visit

•Define & Classify Stream

•Evaluate Stream Stability

•Assess Stream Response

•Establish Level of Analysis

•Bridge Type•Scour Susceptible

Hyd

rolo

gic

, H

ydra

uli

c an

d S

co

ur

An

aly

sis

•Hydrologic Analysis

•Hydraulic Analysis

•Riverine or Tidal •Scour Analysis from Structural or Geotech Data

•Plot Scour Prism•Multi-discilinary Evaluation (Hydraulics, Structures & Geothecnics

•Structure Stable (Low risk or New Bridge)

•Scour Critical: Plan of Action Required

•Countermeasure Viable ( if no, replace bridge)

Bri

dg

e S

co

ur

an

d S

trea

m In

sta

bil

ity

Co

un

term

eas

ure

s

•Develop Plan of Action

•Evaluate Countermeasure options with Matrix

•Select Countermeaure Type (Structural or Hydraulic)

•Design CM or Plan Monitoring

•Evironmental Considerations and Permitting

•Evaluate CM Impact

•Acceptable CM Impact

•Install CM or Implement Monitoring Plan

•Inspection and Maintenance

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FHWA HEC-23 also includes specific Design Guidelines for the most common and some uncommon countermeasures used by DOTs, or references to sources of design guidance. Inherent in the design of any countermeasure are an evaluation of potential environmental impacts, permitting for countermeasure installation, and redesign, if necessary, to meet environmental requirements. As shown in the flow chart (Figure 20.0), to be effective most countermeasures will require a monitoring plan, inspection, and maintenance. The Plan of Action for countermeasures is attached in Appendix F.

2.10.3 Bridge Protection Measures Bridge Embankment is a bank of earth constructed above the natural ground surface to carry a road or to prevent water from passing beyond desirable limits also known as a bank when used as erosion protection structure along the river bank. Riverbank is the earth along the waterline along each side of the waterway. It demarcates the water from the earth and naturally sets the limit to the width of the river channel and determines the flow direction of the river. Suitable earth material has been used in the construction of many engineering structures such as gravity earth-fill dams, road construction material, brickmaking and bridge construction. Bridge approach embankments on each approach help the vehicle or pedestrian to access the bridge from the road. It is basically a link between the roadway and the bridge carriageway through the abutment. The embankment is as important as the superstructure itself as without it, the bridge is just another decoration of the river (Figure 22.0).

Figure 22.0. Shows damaged embankment of Girua Bridge in Oro Province

Destruction of bridge embankments and erosion of riverbanks by the flood is always faced in all bridge sites with natural rivers in Papua New Guinea. The flow characteristic of a natural river is ever-changing after each flood event and does not flow in one particular direction. It is very complex to determine the flow direction of a natural river when undertaking bridge hydraulic design. Almost all bridges in PNG are constructed over a natural river than between valleys, gorges or canals.

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Hence, bridge approaches are washed out during a major flood event, leaving the bridge vulnerable to further damage and causing a high risk of traffic accidents by travelling public. Proper assessment, design and application of appropriate engineering techniques in constructing bridge embankment and riverbank protection structures are a subject that must be pursued. Application of levees, ripraps and groynes in the protection of bridge embankments and riverbanks are options that have been considered over time. However, construction materials and construction methods that are used in the construction of such erosion protection structures are sometimes questionable when they do not perform as expected. Some of these construction methods and materials are not accessible to developing countries like Papua New Guinea where funding is always a challenge. The classes of countermeasures identified for bank stabilization and bend control are bank revetments, spurs, bendway weirs, longitudinal dikes, vane dikes, bulkheads, and channel relocations. Also, a carefully planned cut-off may be an effective way to counter problems created by meander migration. These measures may be used individually or in combination to combat meander migration at a site. Some of these countermeasures are also applicable to bank erosion from causes other than bend migration. The time is right that further studies must be explored to provide simple construction procedures and locally available material that are economical and sustainable to be used in the construction of this vital infrastructure.

2.11 Riverbed Aggradation and Degradation Aggradation can be caused by changes in climate, land use, and geologic activity, such as volcanic eruption, earthquakes, and faulting. For example, volcanic eruptions may lead to rivers carrying more sediment than the flow can transport, this leads to the burial of the old channel and its floodplain. For instance, the quantity of sediment entering a river channel may increase when climate becomes drier. The increase in sediment is caused by a decrease in soil binding that results from plant growth being suppressed. The drier conditions cause river flow to decrease at the same time as sediment is being supplied in greater quantities, resulting in the river becoming choked with sediment. Typical aggradational environments include lowland alluvial rivers, river deltas, and alluvial fans. Aggradational environments often undergo slow subsidence which balances the increase in land surface elevation due to aggradation. After millions of years, an aggradational environment will become a sedimentary basin, which contains the deposited sediment, including paleochannels and ancient floodplains.

2.11.1 What is Aggradation and Degradation? Aggradation or alluviation is the term used in geology for the increase in land elevation, typically in a river system, due to the deposition of sediment. Aggradation occurs in areas in which the supply of sediment is greater than the amount of material that the system is able to transport. The mass balance between sediment being transported and sediment in the bed.

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Degradation refers to the lowering of a fluvial surface, such as a stream bed or floodplain, through erosional processes. It is the opposite of aggradation. Degradation is characteristic of channel networks in which either bedrock erosion is taking place, or in systems that are sediment-starved and are therefore entraining more material than is being deposited. When a stream degrades, it leaves behind a fluvial terrace as illustrated in the figure below.

Figure 23.0 Aggradation and Degradation in river channel

In aggradation the stream's gradient steepens due to increased deposition of sediment while on the other hand, in the degradation process the stream's gradient becomes less steep, due to the erosion of sediment from the stream bed and generally follows a sharp reduction in the amount of sediment entering the stream. Mugade and Sapkale (2015) presented that Aggradation and Degradation are the fluvial processes mostly associated with a river and its differentiating parameters. Aggradation and degradation are generally influenced by river discharge, sediment load, morphological characteristics of river channel and human interventions. If the river water is unable to transfer the bed load or the channel material then the same is deposited within the channel and channel height increases, aggradation occurs. This also leads to change the river morphology and hydraulic geometry. Degradation is another process which is responsible for the lowering of river bed and also shifting the channel banks. This section will review and present methods of improving aggradation and degradation and their influence on the river channel and the necessary bridge countermeasures against them.

2.11.2 Degradation Countermeasures In Papua New Guinea riverbed elevation instability problems are common on alluvial streams due to the geology and geographical characteristics of the river systems. Degradation in streams can cause the loss of bridge piers in stream channels and can contribute to the loss of piers and abutments located on caving banks. Countermeasures used to control bed degradation include check dams and channel linings. Check-dams and structures which perform functions similar to check-dams include drop structures, cut-off walls, and drop flumes. A check-dam is a low dam or weir constructed across a channel to prevent upstream degradation.

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Channel linings of concrete and riprap have proved unsuccessful at stopping degradation. To protect the lining, a check-dam may have to be placed at the downstream end to key it to the channel bed. Such a scheme would provide no more protection than would a check dam alone, in which case the channel lining would be redundant. Bank erosion is a common hydraulic hazard in degrading streams. As the channel bed degrades, bank slopes become steeper and bank caving failures occur. The USACE found that longitudinal stone dikes, or rock toe-dikes provided the most effective toe protection of all bank stabilization measures studied for very dynamic and actively degrading channels.

2.11.3 Aggradation Countermeasures Aggradation causes the loss of waterway opening in bridges and, where channels become wider because of aggrading streambeds, overbank piers and abutments can be undermined. At its worst, aggradation may cause streams to abandon their original channels and establish new flow paths which could isolate the existing bridge. Currently, measures used in Papua New Guinea to alleviate aggradation problems at highways include channelization, debris basins, bridge modification, and continued maintenance, or combinations of these. Channelization may include dredging and clearing channels, constructing small dams to form debris basins, constructing cut-offs to increase the local slope, constructing flow control structures to reduce and control the local channel width, and constructing relief channels to improve flow capacity at the crossing. Except for debris and relief channels, these measures are intended to increase the sediment transport capacity of the channel, thus reducing or eliminating problems with aggradation. Cut-offs must be designed with considerable study as they can cause erosion and degradation upstream and deposition downstream. The short term, maintenance programs prove to be very cost effective when compared with the high cost of channelization, bridge alterations, or relocations. When costs over the entire life of the structure are considered, however, maintenance programs may cost more than some of the initially more expensive measures. Also, the reliability of maintenance programs is generally low because the programs are often abandoned in the case of Papua New Guinea due to budgetary or priority reasons by the government. However, a program of regular maintenance could prove to be the most cost efficient solution if analysis of the transport characteristics and sediment supply in a stream system reveals that the aggradation problem is only temporary perhaps the excess sediment supply is coming from a transient land use activity such as logging or will have only minor effects over a relatively long period of time.

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FHWA (HEC-23, 2009), stated that an alternative similar to a maintenance program which could be used on streams with persistent aggradation problems, such as those on alluvial fans, is the use of controlled sand and gravel mining from a debris basin constructed upstream of the bridge site. Use of this alternative would require careful analysis to ensure that the gravel mining did not upset the balance of sediment and water discharges downstream of the debris basin. Excessive mining could induce degradation downstream, potentially impacting the bridge or other structures. The table below provides the summary of aggradation and degradation countermeasures as reported in FHWA, HEC-23, 20019. Table 9.0 Summary of Aggradation and Degradation Countermeasures

Item Aggradation Countermeasure Degradation Countermeasure 1.0

Extensive channelization projects have generally proven unsuccessful in alleviating general aggradation problems, although some successful cases have been documented. A sufficient increase in the sediment carrying capacity of the channel is usually not achieved to significantly reduce or eliminate the problem. Channelization should be considered only if analysis shows that the desired results will be achieved.

Check-dams or drop structures are the most successful technique for halting degradation on small to medium streams.

2.0

Alteration or replacement of a bridge is often required to accommodate maximum aggradation depths.

Channel lining alone may not be a successful countermeasure against degradation problems.

3.0

Maintenance programs have been unreliable, but they provide the most cost-effective solution where aggradation is from a temporary source or on small channels where the problem is limited in magnitude.

Riprap on channel banks and spill slopes will fail if unanticipated channel degradation occurs.

4.0

At aggrading sites on wide, shallow streams, spurs or dikes with flexible revetment have been successful in several cases in confining the flow to narrower, deeper sections.

Successful pier protection involves providing deeper foundations at piers and pile bents.

5.0

A debris basin and controlled sand and gravel mining might be the best solution on alluvial fans and at other crossings with severe problems.

Jacketing piers with steel casings or sheet piles has also been successful where expected degradation extends only to the top of the original foundation.

6.0

The most economical solution to degradation problems at new crossing sites on small to medium size streams is to provide adequate foundation depths. Adequate setback of abutments from slumping banks is also necessary.

Rock-and-wire mattresses are recommended for use only on small (100 ft [<30 m]) channels

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7.0 experiencing lateral instability and little or no vertical instability.

8.0

Longitudinal stone dikes placed at the toe of channel banks are effective countermeasures for bank caving in degrading streams. Precautions to prevent outflanking, such as tiebacks to the banks, may be necessary where installations are limited to the vicinity of the highway stream crossing.

2.12 Specific Design Considerations Bridge design engineers must analyze the stability of the bridge as a whole and elements of the bridge under various loading conditions. Rivers, streams and coastal water bodies exert significant forces on bridge structures especially during times of flood or storm surge. The hydraulic forces potentially acting on a bridge include hydrostatic, buoyancy, drag and wave forces. Impact by vessels and forces exerted by debris or ice are also closely tied to hydraulics. Bridge designers require information from the results of the hydraulic analysis to evaluate the hydraulic forces on bridge elements.

2.12.1 Hydrostatic Force The weight of water exerts hydrostatic pressure in all directions. It is calculated as the product of the height of the water surface above the point of interest and the unit weight of water. Thus the pressure is greatest at the lowest point of a submerged element and is zero at the water surface elevation. The hydrostatic force acting on a bridge element in a particular direction is the summation, or integral, of the product of the pressure and the surface area of the bridge element projected in the plane perpendicular to the direction of the force. Hydrostatic forces on one side of a bridge are at least partly balanced by opposing hydrostatic forces acting on the other side. Any imbalance in the hydrostatic force is due to variation in the water surface elevation. Bridge designers must be informed of the water surface elevation upstream and downstream of the bridge for the design flood in order to evaluate the hydrostatic forces.

2.12.2 Buoyancy Force Buoyancy is an uplift force equivalent to the weight of water displaced by the submerged element. It can be a threat to a submerged bridge superstructure if the superstructure design incorporates large enclosed voids as with a box-girder or if air pockets develop between girders beneath the deck. Buoyancy is also a factor in evaluating wave-related forces on bridge decks, discussed later in this chapter. If a pier is constructed with a large empty void, the buoyant uplift force acting on the pier may be significant. Bridge designers must be informed of the water surface elevation upstream and downstream of the bridge for the design flood in order to evaluate the buoyancy forces.

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2.12.3 Stream Pressure and Lift Force Stream pressure is the name in the LRFD Specifications for the pressure associated with the drag exerted on the structure by flowing water. By the LRFD Specifications, the stream pressure on a bridge element is computed as a simple function of the square of the impinging flow velocity multiplied by a drag coefficient. Stream Pressure on Piers The drag coefficient for piers is a function of the shape of the pier nose (upstream end), the plan view shape of the pier, the skew (if any) of the pier axis versus the flow direction, and the presence or absence of debris on the pier. The hydraulic engineer must inform the bridge designer of the magnitude and direction of the local impinging flow velocity for the design event, as well as the flow depth and debris collection potential, in order to evaluate the stream pressure on a pier. Stream Pressure and Lift on Bridge Superstructures Recent research provided by FHWA refined guidance on evaluating the stream pressure and forces acting on submerged bridge superstructures. The FHWA (2009) used physical modelling and three-dimensional computational fluid dynamics (CFD) modelling to investigate the hydrodynamic forces on inundated bridge decks, specifically the drag force acting parallel to the flow direction and tending to push the superstructure off of the piers and the abutments; lift force acting vertically and tending to lift the superstructure; and the overturning moment resulting from unevenly distributed forces and tending to rotate the superstructure about its centre of gravity. The physical modelling and CFD modelling both focused on three different superstructure design types: one with six flanged girders, one with three larger rectangular girders, and a third with a highly streamlined cross sectional shape. The resulting report, entitled "Hydrodynamic Forces on Bridge Decks" (FHWA 2009c) provides equations for use in determining the drag coefficient, lift coefficient and moment coefficient as functions of the inundation ratio, for each of the three superstructure types investigated. The inundation ratio is a measure of the degree of submergence of the superstructure. It is defined as the vertical distance measured down from the water surface to the bridge low chord divided by the depth of the superstructure measured vertically from the top of the parapet to the low chord. For the six-girder superstructure, the equations yield drag coefficients roughly ranging from 0.7 to 2.2. For inundated bridge decks, lift is another force component that should be considered in bridge design. FHWA (2009) provides equations for lift, as well as the resulting turning moment that the combined drag and lift forces create. The deck may not react as a single unit depending on the interconnection of the girders, so lift and drag may be more severe for individual deck elements. The hydraulic engineer must inform the bridge designer of certain information from the hydraulics analysis to determine these forces. The required

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information includes the water surface elevation, depth and velocity upstream of the bridge, along with the elevation of the bridge low chord. It will be necessary to qualitatively adjust the drag coefficient to accommodate a bridge superstructure type other than a six-girder or three-girder bridge design.

2.12.4 Wave Forces The design of bridges in coastal settings must consider the potential for significant wave forces. The FHWA document HEC-25 "Highways in the Coastal Environment" (FHWA 2008), documents extensive damage incurred by bridges along U.S. gulf coast during Hurricane Ivan in 2004 and Hurricane Katrina in 2005. The landfall of each hurricane caused a high surge in the water level, allowing the large waves generated by the storm to affect the superstructures of bridges (FHWA 2008). Waves striking a bridge superstructure impart forces acting both horizontally and vertically. The magnitudes of the forces depend upon several factors including the tide level, storm surge, and properties of the anticipated waves. The FHWA conducted a pooled-fund study to develop guidelines and specifications for the design of bridges subject to wave forces in coastal settings. The resulting recommendations were published by AASHTO in the document "Guide Specifications for Bridges Vulnerable to Coastal Storms," (AASHTO 2008). A bridge designer following this AASHTO document requires certain information about the tidal hydraulics and the wave setting. The hydraulic engineer should be prepared to provide the following information, with input from a coastal engineer:

Maximum probable wave height for the design event Wave length Wave period Upwind fetch over which wave can be generated Storm tide water surface elevation at the bridge for the design event,

including local wind setup where appropriate Stream bed elevation at the bridge, and Current velocity from tidal hydraulic modeling for the design event.

The wave height and other wave properties can be computed using equations from the Shore Protection Manual (USACE 1984) or from the Coastal Engineering Manual (USACE 2008) or determined through the application of numerical wave modeling software. The wave properties are generally dependent upon the wind speed, duration and direction, the upwind fetch length, the water depth at the bridge and the water depth over the fetch.

2.12.5 Effects of Debris Debris accumulations on bridges can dramatically increase the hydraulic forces exerted on both piers and superstructures. The LRFD Specifications provide guidance on incorporating debris potential into the stream pressure

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calculations, with respect to assigning a drag coefficient and estimating the cross sectional area of the debris blockage. A research project by the NCHRP used physical modeling to examine debris forces on bridges. The report, titled "Design Specifications for Debris Forces on Highway Bridges," (NCHRP 2000, Report 445) recommends separate evaluation of the drag force and hydrostatic force from debris accumulations. For evaluating the drag force, the report provides envelope curves and tables to aid in assigning the drag coefficient for debris on piers and superstructures as a function of the amount of blockage caused by the debris and the Froude number in the contracted section. The report also provides useful guidance on the selection of the reference velocity for use in the drag force, or stream pressure, calculations. The hydrostatic force is calculated based on the difference in water surface from the upstream side of the debris accumulation to the downstream side of the bridge. Moreover, another research project by the NCHRP used field observations, a photographic database and extensive physical modeling to investigate the effects of debris on bridge pier scour. The resulting report, titled "Effects of Debris on Bridge Pier Scour," (NCHRP 2010b, Report 653) provides refined guidance on estimating the potential dimensions of a debris flow blockage, on incorporating debris into one- and two-dimensional hydraulic models, and on computing an effective pier width for pier scour calculations based on the estimated debris dimensions. When the potential for debris accumulation on the bridge is significant, the hydraulic engineer should be prepared to provide the bridge designer with the estimated dimensions and reference elevation of the potential debris blockage. The hydraulic engineer should also recommend an appropriate drag coefficient for the debris, based on NCHRP Report 445.

2.12.6 Effects of Ice When ice accumulates at a bridge and forms a substantial ice jam, significant problems can develop. Some of the negative consequences include bridge scour and bank erosion, even during times of low streamflow. Ice jams also impart significant lateral forces on the bridge. Similar to debris blockages, ice jams magnify the stream pressure forces by increasing the surface area to which the stream pressure is applied. The upstream water surface elevation (and consequently the hydrostatic force) is affected by the inordinate amount of backwater that often accompanies ice jams. The elevation at which ice is expected to accumulate has a significant influence on the bridge stability calculations. Extensive discussion on evaluation of ice forces is provided in the LRFD Specifications. The design team should perform site-specific research to assess whether ice jamming is a relevant concern. If it is a concern, the hydraulic engineer may be required to develop hydrologic and hydraulic information to assist the bridge designer in evaluating ice forces. It may be beneficial, for instance, to determine the months of the year when ice jamming is most likely to occur. Streamflow records would then be studied to assess the potential for flooding during the most likely ice jamming months, and to identify a streamflow rate that

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represents a reasonable yet conservative flow rate for assessing the potential elevation of an ice jam on the bridge. Field reconnaissance may reveal evidence of the elevation range within which ice jams typically form. The Transportation Association of Canada has published the "Guide to Bridge Hydraulics" (TAC 2004), which includes information on estimating the stage and thickness of ice jams. If needed, the hydraulic engineer can develop hydraulic model simulations of ice jam situations. The HEC-RAS program includes the capability to incorporate ice cover into its simulations. Ice can exert other forces on a bridge besides the increase in stream pressure and hydrostatic force mentioned above. Large ice floes striking bridge piers can generate significant impact forces. Large sheets of ice can experience thermal expansion, generating lateral pressure on the bridge. Ice adhering to the bridge structure during water level increases can impart uplift forces. The hydraulic engineer should be prepared to assist the bridge designer in assessing the potential range of water levels associated with these forces.

2.12.7 Vessel Collision When a bridge is to cross a navigable waterway, the design should consider the potential for impact forces from vessel collisions. Bridges should be designed, wherever practicable, to minimize the probability of a vessel impact. Advisable practices include providing appropriate vertical clearance above the water surface, keeping piers as far away from navigation channels as practicable, and avoiding the placement of piers near a bend in a navigation channel. Navigating large ships and barges can be very difficult, especially at bends, and especially in high-velocity waterways. Locating one or more bridge piers near a bend in a high-velocity waterway with barge or ship traffic dramatically increases the risk of a vessel impact. After taking appropriate precautions in locating the bridge and bridge piers, it is still necessary to allow for some probability of vessel collision. The type of vessel to be considered depends upon the waterway being crossed and the typical boat traffic. The LRFD Specifications provide significant guidance on selecting an appropriate design vessel and assessing the probability of a vessel collision. The bridge designer typically evaluates more than one vessel collision scenario. One potential scenario spelled out by the LRFD Specifications is a case of an empty barge breaking free from its mooring and hitting a bridge pier under peak 100-year flood conditions. The flood conditions include the presence of half of the long-term scour and half of the flood-specific scour at the time the vessel strikes the pier. The hydraulic engineer should inform the bridge designer about the peak 100-year flood velocity, flow direction, depth, water surface elevation and total scour to enable evaluation of the impact force. The required velocity is the local velocity impinging on the pier in question. It is usually appropriate to report the same velocity, flow direction and depth that were used in the scour calculations when providing information for vessel impact forces under flood conditions.

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Another commonly considered case is a fully loaded vessel motoring along the navigation channel and errantly striking the bridge during typical waterway conditions. The LFRD Specifications state that the appropriate velocity and water surface for such a scenario are those associated with yearly mean conditions, combined with half of the estimated long-term scour depth. If streamflow records are available for the stream reach being crossed, the annual mean of the daily mean flow rates can be used to represent yearly mean conditions. In a tidal waterway it is more meaningful to select one or more specific tidal levels, such as mean high water, to represent typical waterway conditions. Some bridge pier locations, for instance in the vicinity of seaports or major shipping channels, may be exposed to very large vessel impact forces that cannot readily be accommodated in the bridge structure design. In such cases it is common to incorporate separate structural dolphins, with or without fender racks, to prevent a bridge impact. Care should be taken in the design of dolphin installations to avoid aggravating the scour potential at the bridge piers they are protecting.

2.13 Summary of Related Literature Review Hydraulic studies of bridge sites are a necessary part of a bridge design. These studies should address both the sizing of the bridge waterway opening to minimise adverse impacts to upstream and downstream landowners and are required such that the foundations can be designed to be safe from scour. The scope of the hydraulic analysis should be commensurate with the complexity of the situation, the importance of the highway, and consequences of failure in its service life. Sham et al (2010), embarked on the importance of thorough study and design of firm bridge foundations that is able to withstand all applicable forces of nature on the structure during the design of Padma Main Bridge in Bangladesh. Proper foundation design and assessment do not only extend the longevity of the structure in its service life but decrease the maintenance and operational cost, lowers the accident risks, create better economic recovery of construction cost and provide a safe environment for the lives of people. The most common cause of highway bridge failure is due to adverse hydraulic action during floods. It is, therefore, essential that sufficient attention is paid to the prevention of such failure when designing new bridges over rivers, estuaries or flood plains. A bridge's vulnerability to damage, or loss, as a result of flood needs to be minimised. Consideration must be given to the limitations and gaps in existing knowledge when using currently available formulas for estimating design flood. The interdisciplinary team needs to apply engineering judgment in comparing results obtained from scouring computations with available hydrologic, hydraulic data and conditions at the site to achieve a reasonable and prudent design.

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Scottish Design Manual for Roads and Bridges Volume 1 (1994) emphasised that the design of bridges across watercourses requires a multi-disciplinary approach, involving structural, geotechnical as well as specialist hydrological and hydraulics expertise so that the bridge is designed to resist the flooding river in its service life both in serviceability and ultimate limit states.

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Chapter 3.0 Research Methodology

3.1 General Overview of Research Methods The methodology section of this research will look at the data collection methods, site investigation, software and other alternative research methods that will enable this research to produce the results and outcomes it pursues. The research methods in this study will be in three folds:

1. Firstly, is to undertake a Field Site Investigation and Assessment of relevant bridges that were damaged by a flood in Papua New Guinea and Japan.

2. Secondly, from the site investigation reports and inspections will analyze the data and interpret them in accordance with the scope if this study.

3. Finally, from the assessments and comparison of the results, this study will develop a set of Flood Resistant Bridge Design Guidelines for Papua New Guinea.

3.2 Research Schedule The research will be carried out in the period of Two (2) Years and Six (6) Months, which is a total of 130 weeks and will be submitted in March 2019 or according to the time and date set by Dean and the Graduate School of Engineering Thesis Committee. However given below is the tentative research schedule to be implemented in this research time frame. Table 10.0 Tentative Research Schedule

Item Activity Year Time Frame Month 1.0 Research Proposal 2016 4 weeks October 2.0 Literature Review 2016 - 2017 20 weeks Nov - Mar 3.0 Bridge Site Inspection

and Investigation 2017 16 weeks Apr - July

4.0 Compilation of Site Investigation Reports

2017 8 weeks Aug - Sep

5.0 Bridge Design and Modeling

2017 - 2018 16 weeks Oct - Jan

6.0 Experiments 2018 16 weeks Feb - May 7.0 Final Write-up 2018 - 2019 50 weeks June - Mar

The schedule is tentative and is subject to change. The university calendar and faculty’s programs will dictate the schedule. This logical timeframe is prepared in such a way that Site Inspections will be carried out after the Winter Season as undertaking inspections during the season is not possible. It includes the National Public Holidays and University sanctioned holidays, hence it is intended as a guide only and shall not be taken as actual activity plan.

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3.3 Site Inspection Procedure The study propose to undertake six (6) bridge site investigations to gather appropriate information required to complete this research. It is intended that three (3) bridges each in Papua New Guinea and Japan will be investigated and required information will be collected. During the site visit the researcher will use a Bridge Inspection Forms and Visual Assessment and measurement of recordable data technique to gather the information required. This will involve a detail collection of all possible information required to develop the possible flood damage causes of the bridge. This research will use the Department of Works – PNG, Bridge Inspection Manual, (2005) procedures to undertake the site inspections with the assistance of Japan Highway Authority or Ministry of Public Works. The Site Inspection will be undertaken in an organised manner in which all public authorities concerned and contractors will be informed of the proposed site visit with a defined plan. The sites to be visited will be organised with the assistance of the Research Supervisor and the relevant authorities responsible for planning the trip and executing it. Once all that is confirmed a site inspection plan will be designed for implementation. Before the visit, a Site Inspection Plan will be drafted including the nominated sites, date and timing of visits and locality map of all sites. From there, the staff and the equipment requirements will be determined and the program will be a review to suit the available resources. The researcher will make sure the progress of the program is monitored so that the budget and the time constraints are met. The inspection plan will make sure the following external factors that may affect the inspections are considered. This includes:

Traffic Restrictions Access Difficulties Safety of Staff undertaking the Inspections Specialised equipment or personnel such as divers may need to be

called upon Seasonal or tidal restrictions Weather Conditions and Availability of vehicles and other logistics

In any case, where information that this research required is available with the local or public authority responsible for the bridges and can be sourced from them, then the inspections will not be carried out but a site familiarisation visit will be undertaken instead. However, if the inspection is not possible due to external factors as stated, the researcher will work with the Research Supervisor to consider alternative options. All in all, this research will follow the Detail Engineering Inspection Procedure of the Department of Works – PNG Bridge Inspection Manual as stated in Chapter 6.0 of the document. The Detailed Engineering Inspection Form is attached in Appendix A.

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Table 11.0 Site Inspection General Outline

Purpose

The detail engineering inspection undertaken in each selected flood affected bridge sites is to observe and gather information on the possible bridge failure cases induced by the flood. It is also intended to observe the bridge site conditions, including the environment, development activities and social aspects of the bridge so that the researcher can better comprehend the contributing factors relating to the damage.

Scope

The scope and the extent of the inspection are only limited within this research area. All information collected will be for the purpose of the study and will not be used in any way as per the Japan Copyright Law. The inspection will heavily depend on nature, extent, magnitude and severity of the damage, which means the severe the damage, the more detail assessment will be carried out.

Procedure

All inspection procedure will be in accordance with the Department of Works Bridge Inspection Manual and the relevant Japan Bridge Inspection Guidelines with respect to each individual site. Since this study is intended to address issues faced in Papua New Guinea but undertaken in Japan, thus both countries road and bridge regulations will be considered and whichever applicable will be used.

Deliverables

From the data, site observations and compiled investigation report in Chapter 4. 0; I will propose several flood resistant bridge design model and conduct the experiment in the laboratory. The model that best fits the flood conditions will be accepted as the recommended model of this research.

3.4 Site Investigation Reports All site investigation reports will be detailed in Chapter 4.0 and will be in accordance to the Detail Engineering Inspections undertaken for each bridge sites. This will be a formal report discussing all engineering aspects of the inspections. The outline of the Bridge Engineering Inspection Report will be as follows but not limited to:

Introduction Locality Map Bridge Inspection and Investigation River Hydraulics and Hydrology Geology and Geomorphology Recommendations and Discussions

3.5 Data Analysis Procedure From the information and recommendations from the detailed Bridge Engineering Inspection Reports, the study will analyze the bridge information

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collected and categorized them in different bridge damage types such as Hydraulics, Geotechnical, Structural, etc. The information on each bridge assessed will look at what bridge element or member were affected or damaged and will compare the causes of the damages and determine the appropriate flood resistant design improvement method to improve it. The two sets of data collected from PNG and Japan will be analyzed to note the similarities and differences that will develop a better guidelines that is applicable for this study. The design information and maintenance techniques used inn those inspected bridges will form part of the study to see how we can improve the maintenance methods and procedures. The general data analysis procedure will be as follows:

Figure 24.0 Data Analysis Procedure

Chapter 4.0 Site Investigation Reports

1• Conduct the site Investigation in PNG and Japan

2• Analysis the data and categorize them

3

• Review the design of bridges and compare with the other relavent codes, practices and research papers gloabally.

4

• Select the most suitable and applicable solutions and recommendations.

5• Develop the Flood Resistant Bridge Design Guidelines for PNG

6

• Submit the paper for review and approval. • Draft a Policy Paper for implementation in PNG.

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4.1 Introduction Site Investigations are carried out basically to collect the field information required for the design of structures. However, in this case, the investigation and site inspections that will be carried out is basically to investigate the damages caused by a flood on the bridges and assess the severity of the damages on each structural member and the causes of damages. The inspections will be carried as outlined in Chapter 3.0 using the Department of Works Detail Engineering Inspection procedure. The format of the inspection form is attached in Appendix A. The site visits will provide other important issues such as upstream and downstream developments, urbanisation effects, agricultural and deforestation activities near or in the catchment areas of the bridge site. Undertake different river cross-section measurements and record every detail of measureable data.

4.2 Locality Map The locality map of a bridge site is a diagrammatic representation of the area where the bridge is located with respect to the region or country. It depicts the land use features, roads, farmland, river, towns, villages, etc. It provides the physical information of the site so that proper assessment of bridge site location and the road alignment are set out in accordance with the flow direction of the river. The maps will be useful for the calculation of the peak design charges to compare with the original design information for comparison and recommendation. All locality maps of the sites studied will be presented in an accepted format and available scale as required of this study. Further request of this information will also be required from the authority or contractor in charge of the site inspected. The maps will make up the appendix of this document.

4.3 Bridge Inspection and Site Investigation The bridges recommended for this study will be inspected at the appointed schedule with the assistance of appropriate authorities. The sites will be inspected as per the guidelines of the authorities concern and in accordance with the inspection procedure mentioned in Chapter 3.0 The observations and information gathered will be further used in the reports. This study will also collaborate with other inspections and assessments that may have been undertaken by other people of the damaged site. The reports will be detailed in such a way that all information required in the scope of the inspection is analysed and presented. Locations that require further site investigation and assessment will be planned for required detail investigation if need be. However, all information required will be collected during the first site visits, as budgetary and time requirements may not allow for further investigation.

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The site investigation will use available equipment that is able to collect data for this study such as, tape measure, safety gears, notebooks, survey staff, GPS, rulers, veneer calibre, spade, shovel, sand bags, camera, etc.

4.4 River Hydraulics and Hydrology River Hydraulics and Hydrology as mentioned earlier this document is the study of water and flow characteristics of the body of fluid especially water in bridge engineering. In the site investigation stage of this study, all nominated bridge sites will be thoroughly assessed with regards to its river flow conditions and behaviours. Open channel flow conditions in a natural river differ completely from controlled water flow such as in dams, directed flow, flood control structures and reservoirs, etc. Thus, its flow behaviour, bed degradation, scouring effects and flow directions changes every time when there is a flood. It is one of the directive principles of this research to undertake a full-scale assessment of the river hydraulics and hydrology of the inspected sites to adequately design a flood resistant bridge foundation. As reported in many of the past literature, failure of adequate research and investigation of the river hydraulics has resulted in many of the bridges being damaged by the flood. In this case, the design information of the damaged bridge will be collected from the responsible authority to compare and contrast the differences in the design and the resultant flood that caused the damage. Thus, the assessment will be used as a basis to develop the model for the experiment and observations.

4.5 Geology and Geomorphology Geology is a branch of science that deals with the physical structure of the earth and the substance that makes the earth. Geomorphology is the study of the physical features of the surface of the earth and their relation to its geological structures. Understanding of the surrounding earth’s physical structure and the physical makeup of the soil provides the best information on the foundation design of the structure. The site investigations will observe the physical makeup of the bridge sites and assess their effect on the damage to the bridges. The investigation will further consider collecting soil samples of bridge site if the assessment warrants for further study. The study will consider the subsoil conditions near the bridge site wherever observable or may request for geotechnical reports related to the design and construction of the damaged bridge. The reports will be further assessed to determine their involvement in the weak bridge foundation that is susceptible to flooding. There are some materials that give away easily during the flood and expose the foundation for further attack by flood, whereas some natural soil material is defensive and take some time to be eroded. Thus this study will explore all possible options to work within the natural means to design a flood resistant bridge foundation that is able to withstand the design

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flood. Borrowed material used in bridge embankment fill has succumbed to flood so much that a thorough assessment on the use of borrowed fill material is required.

4.6 Discussions and Recommendations Thus, in all of these inspections and investigation, a full report will be compiled and all possible flood-induced failure cases will be presented. The information and recommendations reached in the study will determine the scope of the experiments, the model configuration and the design. The discussions will state the established findings and the assessment criteria used in ending up with the conclusion. This will include the collected data, site investigation report, observations and measurements undertaken in comparison with the available designed data. The most identifiable results will make the recommendation list and will be used as a guide to undertaking this study. As these studies may not truly reflect the ground conditions faced in Papua New Guinea. The recommendations will be used as a tool with the experience of the researcher regarding the flood affected bridges in PNG and a flood resistant bridge foundation model will be designed and experimented.

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Chapter 5.0 Results and Discussions

5.1 General Overview From all the different bridge investigations, inspections, and data analysis and recommendations, this paper will provide the results of each bridge and discussions will be made. The discussions will basically compare with the related literature that were studied and reported in Chapter 2.0 and other applicable design codes and specifications. The recommendations from the discussions will form the basis of the Flood Resistant Bridge Design Guidelines for Papua New Guinea. The research will be further developed into a policy document for implementation within Department of Works and other related government agencies in Papua New Guinea.

5.2 Results The results will be tabulated as illustrated in the table below and the individual results will be examined against the approved standards and discussions will be made in light of the research and the need for improvement or acceptance will be explored. Table 12.0. Shows the Table of Results format

Bridge No.

Hydraulics Structural Geotechnical Man-made

1 2 3 4 5 6

Total

5.3 Discussions The discussions will form the basis of recommended Flood Resistant Bridge Design Guidelines for Papua New Guinea in Chapter 6.0. Some of the common discussion points for consideration for the design of flood resistant bridge foundation are:

Most rivers beds and banks consist of, more or less, mobile material. During a flood, the bed level may fall as bed material is transported away by the moving water. Construction of bridge foundations within a river can result in an additional lowering of the bed level at the bridge site, which results in the increase of local scouring at bridge foundations.

A bridge constructed on spread foundations will be at serious risk from scouring when the scour level reaches the level of the base of the footing. When a substructure member is subject to lateral loads, which

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are partially or wholly resisted by resultant soil pressure, then the foundation may be at risk before scour reaches the footing level. Hydrodynamic effects may increase such lateral forces. The bearing capacity of a foundation may also be reduced due to a loss of overburden caused by scouring.

Scour adjacent to a piled foundation may result in a loss of skin friction

and reduction in load-bearing capacity of the piles, even if they have been only partially exposed. Additional bending stresses may also be induced in the piles due to hydrodynamic forces and the loss of lateral restraint.

Overtopping of the approach roadways and turbulent flow adjacent to

approach embankments can lead to erosion and scour of the side slopes and toes of the embankments. This may lead to instability of the approach embankments and possible loss of the road. Loss of fill material around and behind any wing walls can lead to instability and failure of the wing walls.

Local scour at a bridge pier is normally greatest near the upstream nose

of the pier. However, due to local geometrical effects and the nature of the flow or sediment, there may be cases where the local scour is greatest in other areas adjacent to the pier. This is particularly true if the direction of flow deviates significantly from the pier alignment.

The depth of the foundations is important in determining the risk to a

bridge from a given degree of scour. Deep foundations subject to severe scour may be safer than a shallow footing subject to moderate scouring.

There are a significant number of bridges where the flow is affected by

the tidal action. Depending upon the location of the bridge the predominant discharge can vary between fluvial and tidal. In all cases, the flow will be in at least two different directions at different times and flow patterns may vary significantly.

Most natural rivers tend to change their course with time. One

mechanism by which this occurs is bank erosion. A pier or abutment located on a flood plain or in an estuary may be placed at risk if the main channel moves sufficiently close to cause loss of support or undermining. Bank erosion may occur very slowly or be very rapid. It will normally be most rapid during floods. The rate of bank erosion depends partly on the character of the river.

Water flowing past a bridge pier exerts a force on the pier. This force can

be resolved into two components; one along the direction of flow, which is referred to as the drag force and the other normal to the direction of flow, which is referred to as the lift force.

The ability of a pier to withstand drag and lift forces will depend upon the

construction of the bridge and its foundation details. This ability may be reduced during a flood if significant scour takes place around the base

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of a pier.

Buildup of trash and debris against bridge components can significantly affect the hydraulic performance of bridges. Difficulties are normally associated with small single span bridges, which tend to be more easily blocked than large multi-span structures.

Debris, which is caught against or between piers, can result in enhanced

hydraulic forces by increasing the effective pier width. Floating debris, which collides with piers, can cause dynamic loading. The extent of these forces is not easily predicted and both will usually be most severe when the river is in flood.

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Chapter 6.0 Conclusion and Recommendations

6.1 Conclusion of the Study This study is undertaken to address the ever-increasing flood-damaged bridges in Papua New Guinea. Bridge damage by flooding is so frequent that unless a research is carried to provide some solutions, it will continue to affect the livelihood of people and cost the government unbudgeted expenditures in emergency restoration works. Most restoration works undertaken are very expensive without the proper justification of the cost with no guidelines on long-term improvement of the failed structure. What is now common in Papua New Guinea is we tend to have Reactive Approach to undertake the failing infrastructure maintenance in the country then Proactive Approach to planning and maintain the infrastructure in a more structured way. This research is undertaken in a way to help decision makers to relook on how best to address the problem in a simple innovative engineering approach that is more cost efficient and applicable in the context of PNG. Moreover, this study is undertaken to improve the road construction industry in PNG to develop better resilient methods to improve basic infrastructure that affects the livelihood of people significantly. There is always a better and simple way in addressing everyday engineering challenges, however, we think too big that simple solutions become so simple to be accepted.

6.2 General Flood Resistant Bridge Foundation Design Guidelines The research question that has guided this study was “How can we improve flood damage bridges in Papua New Guinea?” This is a big question and this research alone cannot answer the question. Many researchers have looked at exploring the use different hydraulic design techniques, countermeasures and bridge protection structures in bridge and highway construction over the floodplain and rivers. This study is undertaken to improve the bridge design standards that can withstand the designed flood event in the service life of the structure. Papua New Guinea and other Pacific Island nations are facing continuous adverse weather conditions that suffer the vital infrastructure. Lessons learnt in this study can help pave the way forward for newer approach in bridge design. Bridges should be designed to withstand scour from large floods and from stream instabilities expected over the life of a bridge. Recommended procedures for evaluating and designing bridges to resist scour can be found in FHWA publications HEC-20 (FHWA 2012a) and HEC-18 (FHWA 2012b). The overall design will follow the general procedure shown in the flow diagram in Appendix D. This will involve the calculation of afflux, depth of scouring, various hydraulic loads and the choice of appropriate scour protection measures. The return periods used in the calculations will be as recommended to be based on a range of flood return periods of up to 200 years in order to assess which events produce the worst effects from considering different flow

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velocities and depths. The general flood resistant design guidelines to be determined are as tabulated in Table 5.0. Table 13.0. Presents the general flood resistant design guidelines.

Design Criteria General Design Guideline Comments Design of Afflux

The increase in water level upstream of a bridge over that which would have occurred if the bridge were absent is termed as afflux.

For a given cross-sectional area of an opening, the greater the wetted perimeter, the greater is the afflux. Therefore, it will be considered at the planning stage that a smaller number of large openings are preferable to a larger number of small openings.

There are a number of methods available for calculating afflux. The most widely used are the US Bureau of Public Roads (USBPR) method. This is applicable to bridges with vertical piers and horizontal soffits.

To control the afflux at a bridge crossing, particularly where long embankments across the flood plain are required, it will be necessary to provide additional flood openings. In simple cases, methods of calculating afflux such as the USBPR method can be used to determine the length of openings required. The calculations will indicate the overall length of openings required in achieving a certain afflux but the appropriate location for these openings will depend upon the local geometry.

Design for Structural Stability

In order to satisfy that the structure is adequate to resist against the hydraulic action of flooding water, the structural design will be carried out in this order: Calculate the total potential scour depth and

check that the structural design is adequate with that depth of scour.

Incorporate appropriate scour protection measures in the design such as the bank protection structures.

Calculate the load on the structure and its foundations and check for structural adequacy.

Design of Flow

Calculations will be based on a range of flood return periods of up to 200 years in order to assess which events produce the worst effects from considering different flow velocities and depths.

In this study, the range will be from Q20 – Q200. The reason for this is that in many rivers, velocities can be high when flows are just within

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the banks, and scour can be worse than the higher flooding discharge rates.

Estimating Effects of General and Local Scour

The estimation of scouring effects will involve the following: Obtain all relevant data from the bridge sites Select critical return periods and calculate design

discharge. Draw cross-sections at the proposed bridge site

showing proposed foundation depths. Additional cross-sections will be taken in the neighbourhood of the bridge site, e.g. within approximately 5m river widths upstream and downstream of the bridge site. These areas will be inspected for signs of scour or irregularities, which might influence flow conditions or bed levels at the bridge site.

Decide whether long-term bed level variation such as progressive degradation is allowable.

Calculate design water levels and velocities. Establish or estimate the direction of flow trajectories in relation to the alignment of bridge piers - flow trajectories may be significantly different at various flood conditions than at normal flow conditions.

Calculate hydraulic parameters such as Froude Numbers (Fr) and floodplain or main channel discharge split.

Calculate general scour depths. Redistribute general scour to the most critical bed profile, taking into account the layout of the bridge crossing and its foundation details.

Compare the measurements of bed level at the bridge site with the calculated bed levels.

Calculate local scour at each potentially vulnerable foundation, including abutments. Superimpose local scour upon general scour, assuming the top width of local scours holes, measured from the pier face, to be within approximately 1.0 to 2.8 times the local scour depth.

Interpret scour depths in the light of potential effects upon the structural strength and stability of the foundations.

Progressive Degradation and

Progressive degradation results from modification of the stable regime conditions to which a river has become adjusted. This may be as a result of alterations to water or sediment flows in the river. The result of progressive degradation at a bridge site will be a lowering of bed level, which may place the foundations at risk.

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Aggradation Degradation will normally increase the risk to bridge structures from being scoured, however, in some cases, aggradation may occur - this will cause increased water levels but will probably reduce the risk from scour.

If the channel is expected to degrade, then the estimation of long-term bed elevation will be used to calculate general and local scour depth levels.

Scour Protection Measures for Riverbed and Riverbank

It may not be economical to design the elements of a bridge to withstand the maximum possible scour. However, an alternative is to carry out scour protection works to prevent or reduce scour of the bed and banks. In this study, it is proposed that a scour reduction

structure to be constructed at the top of the pile cap and installed below the riverbed level to reduce local scouring around bridge piers.

Concrete sandbags to be placed along the bridge abutment and the riverbank to prevent scouring at bridge abutments and control bank erosion. Ideally, the concrete sandbag will be abrasion resistant and of sufficient weight to prevent it from being moved by the flow. The size or weight of the concrete sandbag will be designed to be roughly proportional to the sixth power of the flow velocity.

Gabion and grouted mattresses will be placed locally around piers and abutments or across the full width of the inlet to increase the resistance of the riverbed to scour. The riverbed should be pre-excavated so that the mattresses lie below bed level. Mattresses will also be used to protect the riverbanks.

Increase the size of the waterway opening at the downstream end and channel improvements are some methods to resist flood.

Specific Design Considerations for Freed-board, Loads, Hydrodynamic Forces, and Debris Forces

Freeboard will be such that bridge soffit levels at flood spans are 600mm above the design flood level or known maximum flood level on minor watercourses in order to allow floating debris to pass freely through the structure. In determining the freeboard, the allowance will be made for afflux.

Unless otherwise specified, the design checks will be carried out both at the ultimate limit state (ULS) and the serviceability limit state (SIS) using the applicable combination rules and the partial factors of safety.

Hydrodynamic forces from the action of flowing water past the submerged parts of a bridge can

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act in addition to hydrostatic forces. The Indian Road Congress (IRC) and American Association of State Highway and Transportation Officials (AASHTO), recommend the following equation for the hydrodynamic flow pressure P (kN/m2), P = 0.51KU2 to determine the Hydrostatic Pressure.

Debris forces - the type of debris occurring in a river will depend upon the size and characteristics of the river and the area through which it flows. An investigation will be carried out to determine the type and size of floating debris to be expected at the bridge site.

A minimum allowance will be made for a debris collision force equivalent to that exerted by a 3-ton log travelling at the stream velocity calculated for the peak design event and arrested within distances of 150mm for slender column type piers and 75mm for massive, non-yielding type piers.

Spread Footing Foundation on stabilised backfill material.

Different bed materials scour at different rates. Thus, an investigation will be conducted on the riverbed material and design considerations will be undertaken to prevent scouring action on riverbed material near the foundation.

Bridge foundation analysis will be carried out on the basis that all streambed material within the scour prism above the total scour depth will have been removed and is not available for bearing or lateral support.

Spread Footing Foundation on stabilised fill material will be ensured that the abutment foundation footing is below the calculated scour depth.

Ensure that the bottom of the abutment and the retaining wall footing is at least 2 meters below the present streambed level.

Ensure that circular slip-failure of the soil foundation will not occur.

For pile designs subject to scour, consideration will be given to using a lesser number of long piles to develop bearing resistance, as compared to a greater number of shorter piles.

Place the top of the pile cap at a depth, below existing riverbed level; equal to the estimated general scour depth to minimise obstruction to flood flows and its resulting local scour.

Bridge superstructure soffit levels will be positioned above the general level of the approach roadways wherever practicable. In the event of overtopping of approach embankments,

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Bridge Superstructure

this provides for a reduction of any hydraulic forces acting on the bridge. This is particularly important for bridges over rivers or streams carrying large amounts of debris, which could clog the waterway of the bridge.

Bridge superstructures will be securely anchored to the substructure if the deck could become buoyant, or, floating debris is probable. Where overtopping is likely, the superstructure cross-section will be shaped to minimise resistance to the flow.

Bridge Piers

Bridge pier foundations on floodplains will be positioned at the same depth as the pier foundations in the stream channel if there is any likelihood that the channel will shift its location onto the floodplain over the life of the bridge.

Piers will be aligned as far as is practical, in the direction of flood and tidal flows. Assess the hydraulic advantages of different pier shapes, particularly where there are complex flow patterns during floods and use the most appropriate pier shape.

Streamline pier shapes to decrease scour and minimise potential for the build-up of debris.

Evaluate the hazard from debris build-up when considering the use of multiple pile bents in stream channels. Where debris build-up is a problem, the bent will be designed as though it were a solid pier for the purposes of scouring estimation. Consider the use of other pier types where clogging of the waterway area could be a major problem.

Bridge Abutments

Available equations do not satisfactorily predict scour depths for abutments. It is recommended in this study that concrete sandbag riprap or guide banks will be considered for abutment protection. Correctly designed and constructed, the suggested protective measures can negate the need to compute abutment scour.

Relief openings, guide banks and river training works will be used, where necessary, to minimise the effects of adverse flow conditions at abutments.

Scour at spill-through abutments is about half of that for vertical wall abutments, however, consideration will be given to the loss of spill-through embankment material due to scour.

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References The following bibliography contains the main references used in this research proposal.

1. Scottish Design Manual for Roads and Bridges, The Design of Highway Bridges for Hydraulic Action, Volume 1, Section3, Part 6, (1994).

2. I. Zevgolis and P. Bourdeau, Mechanically Stabilised Earth Wall Abutments for Bridge Support, (2007), U.S DOT FHWA, Washington DC, USA.

3. US Army Corps of Engineers, Sandbagging Techniques, (2004), Portland, USA.

4. U.S DOT FHWA, Design and Construction of Mechanically Stabilised Earth Walls and Reinforced Soil Slopes, Volume 1, (2009), Washington DC, USA.

5. WisDOT, Bridge Manual, Chapter 12, (2016), Wisconsin, USA. 6. Sham et al, Foundation Design Methodology for the Padma Main

Bridge, (2010), EACOM Asia Company Ltd, Shatin, New Territory, Hong Kong.

7. U.S DOT FHWA, Evaluating Scour at Bridges, 5th Edition, (2012), Washington DC, USA.

8. http://en.wikipedia.org/wiki/embankments 9. E. Snell and A Smith, The Design of Flood Resisting Bridge Abutments

and approach Embankments, (2012). 10. http://en.wikipedia.org/wiki/bridge_scour 11. European Commission JRC, Seminar on Bridge Design with

Eurocodes, (2012). 12. K. Johnson, Abutments, (2012), MinDOT, Minnesota, USA. 13. http://en.wikipedia.org/wiki/abutment 14. http://en.wikipedia.org/wiki/bailey_bridge 15. U.S DOT FHWA, Hydraulic Design of Bridges, (2012), Washington DC,

USA. 16. R. Davies, Papua New Guinea – 3 Days of Heavy Rain Cause Floods

and Landslides – Several Dead and Bridges Destroyed, (16/10/2016), The Floodlist, Australia.

17. Piellca et al, Flood Damage in the United States 1926 – 2000: A Reanalysis of National Weather Service Estimates, (2012).

18. Department of Main Roads, Bridges and Retaining Walls (Chapter 22), (2006), Queensland, Australia.

19. NSW Transport Roads and Maritime Services, Country Bridge Solutions, Edition 2, Volume 1.2, (2016), Sydney, Australia.

20. S. Yagi, Ramu Highway Upgrade Soon, (27/10/2015), Loop PNG News, Papua New Guinea.

21. PNG Mirror News, Fuel Crisis Looms in Highlands, (3/10/2016), Papua New Guinea.

22. Redcross Society PNG Inc., Papua New Guinea Cyclone Guba Final Report, (2009), Port Moresby, Papua New Guinea.

23. Department of Works, Bridge Inspection Manual, Volume 2, (2005), Papua New Guinea.

24. Markham Culverts Ltd, Tensar Geogrid and Geotextile Guide, (2016), Lae, Papua New Guinea.

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Appendices

Appendix A: Department of Works Bridge Inspection Form

Figure 25.0 DoW Bridge Inspection Form. Source: Department of Works – PNG.

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Appendix B: Tensar Geogrid Specification

Figure 26.0 Tensar Geogrid Specification Notes. Source: Markham Culverts Ltd

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Appendix C: Bidim Non-Woven Geotextile

Figure 27.0 Geotextile Summary Guide for PNG. Source: Markham Culverts Ltd – PNG.

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Appendix D: Preliminary Bridge Hydraulic Design Process

Figure 28.0 Procedure for preliminary hydraulic bridge design. Source: Scottish Design Manual for Roads and Bridges (1994).

Step 0

• Determine the line of highway or road corridor and agree with the client and relevant government authorities and local landowners.

Step 1

• Site reconnaisance • Review and analysis of available river data• Select possible locations for bridge crossing

Step 2

• Undertake the bridge site survey and field study.

Step 3

• Design flood flow• Maximum flood level• Navigational constraints• Riverbed particle size and tractive stress• Approach flow velocity and direction• Floodplain width• River meander characteristics

Step 4

• Waterway opening• General scour depth• Afflux• Flow velocity• River training works requirements

Step 5

• Are afflux & general scour depths acceptable? If answer is no, then adjust waterway opening. If the answer is yes then, proceed to Step 6.

Step 6• Preliminary bridge design including calculation of Hydrodynamic Forces and Forces due to debris, shipping and ice.

Step 7

• Determine the pier geometry and location• Calculate the Genral Scour, Afflux and Local Scour

Step 8

• Are general and local scour depths acceptable? If no, then reduce the genral and local scour effects by adjusting the waterway opening or adjust the pier geometry and number of piers. If yes, then proceed to Step 9.

Step 9

• Is the afflux acceptabel? If no, then adjust the waterway opening if it's located on a floodway crossing or adjust the pier geometry and number of piers. If yes, then proceed to Step 10.

Step 10• Cost the approaches, river training works and bridge structures

Step 11

• Can further adjustments be made to produce a more satisfactory design? If yes, then alter the bridge type, adjust the pier geometry, bridge location or adjust the waterway opening.

• If the answer is no, then proceed to Step 12.

Step 12

• Is there any alternatiive bridge crossing location to be assessed? If yes, then go back to Step 3 and repeat the process. • If no, then proceed to Step 13.

Step 13• Review the alternative premilinary designs and make final selection for detail design and possible model investigation.

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Appendix E: FHWA Scour and Stream Stability Flow Chart

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Appendix F: Standard Template for Scour and Stream Stability Plan of Action

SCOUR CRITICAL BRIDGE - PLAN OF ACTION

1. GENERAL INFORMATION

Structure number:

City, County, State:

Waterway:

Structure name:

State highway or facility carried:

Owner:

Year built: Year rebuilt: Bridge replacement plans (if scheduled): Anticipated opening date:

Structure type: Bridge Culvert Structure size and description: Foundations: Known, type: Depth: Unknown Subsurface soil information (check all that apply): Non-cohesive Cohesive Rock Bridge ADT: Year/ADT: % Trucks: Does the bridge provide service to emergency facilities and/or an evacuation route (Y/N)? If so, describe: 2. RESPONSIBILITY FOR POA Author(s) of POA (name, title, agency/organization, telephone, pager, email): Date: Concurrences on POA (name, title, agency/organization, telephone, pager, email): POA updated by (name, title, agency, organization): Date of update: Items update: POA to be updated every months by (name, title, agency/organization): Date of next update: 3. SCOUR VULNERABILITY a. Current Item 113 Code: 3 2 1 Other: b. Source of Scour Critical Code: Observed Assessment Calculated Other: c. Scour Evaluation Summary: d. Scour History:

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4. RECOMMENDED ACTION(S) (see Sections 6 and 7)

Recommended Implemented a. Increased Inspection Frequency Yes No Yes No b. Fixed Monitoring Device(s) Yes No Yes No c. Flood Monitoring Program Yes No Yes No d. Hydraulic/Structural Countermeasures Yes No Yes No

5. NBI CODING INFORMATION

Current Previous

Inspection date

Item 11 Critical Scour

Item 60 Substructure

Item 61 Channel & Channel Protection

Item 71 Waterway Adequacy

Comments: (drift, scour holes, etc. - depict in sketches in Section 10)

6. MONITORING PROGRAM

Regular Inspection Program w/surveyed cross sections Items to Watch:

Increased Inspection Frequency of mo. w/surveyed cross sections Items to Watch:

Underwater Inspection Required

Items to Watch: Increased Underwater Inspection Frequency of mo.

Items to Watch:

Fixed Monitoring Device(s) Type of Instrument: Installation location(s): Sample Interval: 30 min. 1 hr. 6 hrs. 12 hrs. Other: Frequency of data download and review: Daily Weekly Monthly Other Scour alert elevation(s) for each pier/abutment: Scour critical elevations(s) for each pier/abutment: Survey ties: Criteria for termination for fixed monitoring:

Flood Monitoring Program Type: Visual inspection Instrument (check all that apply): Portable Geophysical Sonar Other: Flood monitoring required: Yes No Flood monitoring event defined by (check all that apply):

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Discharge Stage Elev. measured from Rainfall (in/mm) per (hour) Flood forecasting information: Flood warning system: The frequency of flood monitoring: 1 hr. 3 hrs. 6 hrs. Other: Post-flood monitoring required: No Yes, within days The frequency of post-flood monitoring: Daily Weekly Monthly Other: Criteria for termination of flood monitoring: Criteria for termination of post-flood monitoring: Scour alert elevation(s) for each pier/abutment:

Scour critical elevation(s) for each pier/abutment: Note: Additional details for action(s) required may be included in Section 8.

Action(s) required if scour alert elevation detected (include notification and closure procedures): Action(s) required if scour critical elevation detected (include notification and closure procedures):

Agency and department responsible for monitoring:

Contact person (include name, title, telephone, pager, e-mail):

7. COUNTERMEASURE RECOMMENDATIONS

Prioritise alternatives below. Include information on any hydraulic, structural or monitoring countermeasures.

Only monitoring required (see Section 6 and Section 10 – Attachment F) Estimated cost $

Structural/hydraulic countermeasures considered (see Section 10, Attachment F): Priority Ranking Estimated cost

(1) $

(2)

$

(3) $

(4)

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$

(5) $

The basis for the selection of the preferred scour countermeasure:

Countermeasure implementation project type: Proposed Construction Project Maintenance Project Programmed Construction - Project Lead

Agency: Bridge Bureau Road Design

Other Agency and department responsible for countermeasure program (if different from Section 6 contact for monitoring): Contact person (include name, title, telephone, pager, e-mail): Target design completion date: Target construction completion date:

Countermeasures already completed:

8. BRIDGE CLOSURE PLAN

Scour monitoring criteria for consideration of bridge closure: Water surface elevation reaches at Overtopping road or structure Scour measurement results / Monitoring device (See Section 6) Observed structure movement / Settlement Discharge: cfs/cms Flood forecast:

Other: Debris accumulation Movement of riprap/other armour protection Loss of road embankment

Emergency repair plans (include source(s), contact(s), cost, installation directions):

Agency and department responsible for closure:

Contact persons (name, title, agency/organization, telephone, pager, email):

Criteria for re-opening the bridge:

Agency and person responsible for re-opening the bridge after inspection:

9. DETOUR ROUTE

Detour route description (route number, from/to, distance from bridge, etc.) - Include map in Section 10, Attachment E.

Bridges on Detour Route:

Bridge Number Waterway Sufficiency Rating/ Load

Limitations Item 113

Code

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Traffic control equipment (detour signing and barriers) and location(s):

Additional considerations or critical issues (susceptibility to overtopping, limited waterway adequacy, lane restrictions, etc.) :

News release, other public notice (include authorized person(s), information to be provided and limitations):

10. ATTACHMENTS

Please indicate which materials are being submitted with this POA:

Attachment A: Boring logs and/or other subsurface information

Attachment B: Cross sections from current and previous inspection reports

Attachment C: Bridge elevation showing existing streambed, foundation depth(s) and observed and/or calculated scour depths

Attachment D: Plan view showing the location of scour holes, debris, etc.

Attachment E: Map showing detour route(s)

Attachment F: Supporting documentation, calculations, estimates and conceptual

designs for scouring countermeasures.

Attachment G: Photos

Attachment H: Other information:

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Appendix G: PNG Flood Estimation Manual Tables & Figures Table 14.0 Short Duration Rainfall Ratios (DT,tc/PT)

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Figure 29.0 Map of 2-Year Daily Point Rainfall (P2)

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Figure 30.0 Map of 100-year Daily Point Rainfall (P100)

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Figure 31.0 Short Duration Rainfall Generalized Curves for DT,tc/PT Ratio

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Figure 32.0 Tropical Cyclones and Rainfall Seasonality

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Figure 33.0 Regional Flood Frequency Method Definition of Slope and Shape Indexes

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Figure 34.0 Regional Flood Frequency Method Swamp Adjustment Factor (KS)

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Figure 35.0 Regional Flood Frequency Method Area-P2 Matrix

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Figure 36.0 Regional Flood Frequency Method Area-Slope Matrix

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Figure 37.0 Regional Flood Frequency Method Slope-P2 Matrix

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Figure 38.0 Rational Method Frequency Factors

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