Bulahdelah Upgrading the Pacific Environmental Impact … · Environmental Impact Statement...

Bulahdelah Upgrading the Pacific Highway Environmental Impact Statement Technical Paper 11 Topography, Geology and Soils

November 2004

Roads and Traffic Authority

Parsons Brinckerhoff Australia Pty Limited ACN 078 004 798 and Parsons Brinckerhoff International (Australia) Pty Limited ACN 006 475 056 trading as Parsons Brinckerhoff ABN 84 797 323 433

PPK House 9 Blaxland Road Rhodes NSW 2138 Locked Bag 248 Rhodes NSW 2138 Australia Telephone +61 2 9743 0333 Facsimile +61 2 9736 1568 Email [email protected] ABN 84 797 323 433 NCSI Certified Quality System ISO 9001

58L320A.070 11 - Topography, Geology & Soils Final.doc

Author: Gareth Evans, Paul Hewitt

Reviewer: Mark Keogh

Approved by: Mark Keogh

Signed: ..................................................................................................................

Date: 1 November 2004

Contents Technical Paper 11

Contents

Page Number

1. Introduction 1-1 1.1 Overview 1-1 1.2 Clarification of Government Departments 1-4 1.3 Project Description 1-4

2. Geotechnical Investigations 2-1 2.1 Investigation Methods 2-1 2.2 Desk Study 2-1 2.3 Geological Mapping 2-2 2.4 Subsurface Investigation 2-2 2.5 Soil Contamination Sampling 2-7 2.6 Acid Sulphate Soil and Rock Sampling 2-9 2.7 Laboratory Testing 2-11

2.7.1 Geotechnical Testing 2-11 2.7.2 Soil Contamination Testing 2-12 2.7.3 Acid Sulphate Soil Testing 2-12 2.7.4 Acid Sulphate Rock Testing 2-12

2.8 Reporting 2-13

3. Physical Setting 3-1 3.1 Terrain, Topography and Geology 3-1

3.1.1 Hill Crests and Ridges 3-1 3.1.2 Slopes 3-2 3.1.3 Alluvial Plains 3-3 3.1.4 Backswamps and Backplains 3-4

3.2 Regional Geology 3-4 3.3 Geomorphological Model 3-5

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Bulahdelah – Upgrading the Pacific Highway Technical Paper 11

4. Geotechnical Characteristics of the Proposed Route 4-1 4.1 Interpreted Subsurface Conditions 4-1

4.1.1 Fill 1 4-1 4.1.2 Cut 1 4-1 4.1.3 Fill 2 4-2 4.1.4 Cut 2 4-3 4.1.5 Cut 3 4-4 4.1.6 Cut 4 4-4 4.1.7 Fill 3 4-6 4.1.8 Cut 5 4-6 4.1.9 Fill 4 4-7

4.2 Cut Batter Design 4-8 4.2.1 General 4-8 4.2.2 Classification of materials 4-8 4.2.3 Batter Profiles 4-9

4.3 Colluvium Area Cut 4 4-5 4.3.1 Landslide Risk Assessment 4-7 4.3.2 Colluvium Batter Stability Analysis 4-13

4.4 Batter Protection 4-16 4.5 Excavated Materials from Site 4-17

4.5.1 Characteristics of Excavated Materials 4-17 4.5.2 Unsuitable Material 4-18 4.5.3 Commercial Sources of Construction Materials 4-18

4.6 Embankments 4-20 4.6.1 Settlement Assessment in Fills 4-20 4.6.2 Settlement Analysis 4-21 4.6.3 Stability of Fill Embankments 4-25 4.6.4 Construction on Floodplains 4-28

4.7 Bridge Structures 4-30 4.7.1 Southern Interchange 4-30 4.7.2 Myall River Bridge 4-30 4.7.3 Bombah Point Road Overpass 4-31 4.7.4 Mountain Access Overpass 4-31 4.7.5 Stuart Street Underpass 4-31 4.7.6 Northern Interchange 4-31 4.7.7 Underpass to the Waste Facility 4-32 4.7.8 Frys Creek Bridge 4-32

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Contents Technical Paper 11

4.8 Acid Sulphate Soils 4-32 4.9 Acid Sulphate Rock 4-33 4.10 Contaminated Soils 4-33 4.11 Erosion Hazard 4-34

4.11.1 Hill crests and ridges 4-34 4.11.2 Slopes 4-34 4.11.3 Alluvial Plains 4-34 4.11.4 Backswamps and Backplains 4-34 4.11.5 Management 4-34

5. Impact Assessment and Mitigation 5-1 5.1 Cuttings 5-1 5.2 Embankments 5-2 5.3 Acid Sulphate Soil and Acid Rock 5-3 5.4 Contaminated Soils 5-3 5.5 Soil Erosion and Sedimentation 5-4

6. Further Investigation 6-1

References R-1

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List of Tables Table 1.1: Identified Zones 1-5 Table 2.1: Site Investigation Details 2-2 Table 2.2: Summary of Laboratory Testing 2-11 Table 4.1: Fill 1 Soil Profile 4-1 Table 4.2: Cut 1 Inferred Profile 4-2 Table 4.3: Fill 2 Ground Profile 4-2 Table 4.4: Cut 2 Inferred Profile 4-3 Table 4.5: Cut 3 Inferred Profile 4-4 Table 4.6: Cut 4 Inferred Profile 4-5 Table 4.7: Fill 3 Ground Profile 4-6 Table 4.8: Cut 5 Inferred Profile 4-7 Table 4.9: Fill 4 Ground Profile 4-7 Table 4.10: Material Classification 4-9 Table 4.11: Batter Profile Schedule 4-9 Table 4.12: Recommended Batter Profiles 4-3 Table 4.13: Risks to Individuals in New South Wales 4-10 Table 4.14: Calculated Factors of Safety in Colluvium 4-14 Table 4.15: Calculated Factors of Safety in Colluvium under Seismic Loading 4-14 Table 4.16: Results of Settlement Analysis 4-23 Table 4.17: Summary of Stability Analyses at Design Embankment Height 4-27

List of Figures Chapter 1 Introduction Figure 1.1 The Proposal Chapter 2 Geotechnical Investigations Figure 2.1 Geotechnical Terrain Figure 2.2 Geological Map Figure 2.3 Geotechnical Investigation Test Sites Figure 2.4 Contaminated Land Investigation Test Sites Figure 2.5 Acid Sulphate Soils Risk Map Chapter 4 Geotechnical Characteristics of Proposed Route Figure 4.1 Inferred Boundary of Ancient Landslide Figure 4.2 Recommended Batter Profiles Figure 4.3 Proposed Cut in Favourable Conditions Figure 4.4 Typical Colluvium Boulder and Core Drilled Boulder within Colluvial Soil Photographs Figure 4.5 Potential Hazards Identified in Colluvium Area Figure 4.6 Risk Assessment of Potential Hazards in Colluvium Area Figure 4.7 Operating Quarries and Prospective Quarry Sites

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Glossary Technical Paper 11

Glossary of Terms

Term Meaning

AADT Average Annual Daily Traffic.

Abutment The part of the substructure which that supports the superstructure at its extremities.

Acid sulphate soils (ASS) Acid sulphate soils (ASS) is the common name given to soils containing iron sulphides (principally iron pyrite) or products of the oxidation of sulphides.

ALARP As Low As Reasonably Practicable.

Approach Slabs A reinforced concrete slab spanning from the approach fill to the abutment.

Asphalt or Asphaltic Concrete A mixture of bitumen with a mineral filler and a graded fine and course aggregate, used as a road wearing surface.

ASSMAC Acid Sulphate Soil Management Advisory Committee.

Alluvium A soil which that has been transported and deposited by running water. The larger particles (sand and gravel size) are usually water worn.

Aquifer A layer of rock or soil able to hold or transmit much water.

Atterberg limits A set of arbitrarily defined boundary conditions in soils related to water (moisture) content. The limits are, as follows:

Shrinkage Limit (SL) – The moisture content from which a soil will continue to dry out without further change in volume (rarely determined).

Liquid Limit (LL) – The moisture content at which the soil will flow under a specified small disturbing force (defined by the conditions of the test).

Plastic Limit (PL) – The moisture content at which the soil can be deformed plastically. It is defined as the minimum water content at which the soil can be rolled into a thread 3 millimetres thick.

Plasticity Index (PI) – The range of moisture content over which the soil is in the plastic condition: PI = LL – PL.

Auger drilling A generic term used to describe the method of advancing a borehole using bucket or plate augers or continuous spiral flight augers with the removal of cuttings by mechanical means.

Australian Height Datum (AHD) A level datum, uniform throughout Australia, based on an origin determined from observations of mean sea level at tide gauge stations, located at more than 30 points along the Australian Coastline.

Backfill Fill placed in an excavation.

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Term Meaning

Bank cubic metre The volume of material measured from the design drawings. This measurement makes no allowance for the change in volume due to the type of material being excavated and/or compacted.

Basalt Volcanic extrusive rock type with fine grained structure and dark minerals.

Batter (rake) The uniform side slope of walls, banks, cuttings.

The degree of such a slope, usually expressed as a ration of x horizontal to one vertical in distinction from grade.

Bearing capacity The load per unit area which a supporting medium can carry without failure or unacceptably large settlements.

Bedrock Outcrop of in situ rock material below the soil profile.

Berm A ledge formed at the top or bottom of an earth slope or at some intermediate level.

Borehole A hole produced in the ground by drilling or driving.

Bored pile A pile formed by casting concrete into a hole bored in the ground.

Borehole packer testing Test carried out in unlined boreholes in rock formations using expanding packers to isolate a section of the borehole. High water pressure is then pumped into the section permeability of the rock mass is evaluated based on the volume of water and pressure.

California bearing ratio (CBR) A measure of the bearing capacity of a soil obtained from a standard soil penetration resistance test.

Carboniferous age Geological period of time, ranging from 280–345 million years ago.

Cast-in-Place Cast-in situ

Refers to concrete which is cast directly into its final position.

Clay A natural earthy material possessing plastic properties and consisting of fine particles of complex hydrous silicate smaller than 2 µm.

Cobble A water-worn rounded stone usually between 60 millimetres and 200 millimetres in size.

Cohesion The ability of a material to resist by means of internal forces of attraction the separation of its constituent particles.

Colluvium A soil, often including angular or rounded rock fragments and boulders, which have been transported down slope predominately under the action of gravity assisted by water. The principal forming process is that of soil creep in which the soil moves after it has bean weakened by saturation. It may be water borne for short distances.

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Term Meaning

Compaction (compact)

Reduction in volume of a material by inducing closer packing of its particles by rolling, tamping, vibrating or other processes to reduce the air voids content.

Compaction factor/ratio Ratio of the final volume of the soil to the initial volume, after subjection to compaction of standard form or according to field practice.

Concept design Initial functional layout of a concept, such as a road or road system, to provide a level of understanding to later establish detailed design parameters.

Contract Documents Those documents which that form part of the ‘“Formal Instrument of Agreement’” which is executed between the Contractor and the Principal, and which includes a copy of the Tender, Drawings, Specification, General and Special Conditions of Contract.

Cone penetration test (CPT) A test in which the effort to push or drive a standard steel cone into soil at a controlled rate is used as a measure or to assess certain soil properties.

CPTU Cone penetration test with pore water pressure measurement – a piezocone test.

Consolidation The process by which soil reduces in volume under load over a period of time due to drainage of water from the voids.

Core A piece inserted into a mould for concrete before casting, to form a hole for a bolt, prestressing cable, or other use.

A cylinder drilled out of soil, concrete, rock or other material for testing or other purposes.

Core drilling A generic term used to describe the method of advancing a borehole with a rotary bit and with the removal of cuttings by the circulation of a fluid, and in which the bit is designed to cut an annular hole leaving a central core which is retained in the core barrel to which the bit is attached (generic term).

Culvert A covered channel consisting of one or more adjacent pipes and enclosed cells of rectangular or other shape, for conveying a watercourse or stream below formation level.

Cut The depth from natural surface of the ground to the subgrade level.

The material excavated from a cutting.

Cut batters The side slopes of cuttings.

Cut-off wall A watertight wall for preventing seepage or movement of water under or past a structure, or for preventing scour from undermining a structure.

Cutting An earth or rock excavation within the works site that is made below an existing surface to create the road formation.

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Term Meaning

DCM R44 RTA QA Specification for Earthworks (Cut, Fill, Imported Fill and Imported Select Material).

DCM R50 RTA QA Specification for Stabilisation of Earthworks.

Devonian age Geological period of time ranging from 345 to 395 million years ago.

Dyke Igneous (volcanic) intrusion often near vertical or with a steep dip, occupying a widened fracture in the country rock, and typically cutting across older rock planes.

A low embankment of earth, precast concrete blocks or asphalt near the edge of the formation to control water movement.

EIS Environmental Impact Statement.

Emerson Crumb Dispersion Test This test (at relevant Australian Standard) to determines dispersion characteristics of a soil in distilled water. Soils are soil into divided into seven classes on the basis of their coherence in water with and one further class being distinguished by the presence of calcium-rich minerals . The test is carried out as per the relevant Australia Standard.

Emerson Number Result as determined by the Emerson Crumb Dispersion Test.

External settlement Compression of the sub-surface layers (i.e. external to the fill).

Factor of safety The ratio of load or stress causing failure to the design load or stress.

The ratio of the load causing failure to the actual load.

Fill (filling) The depth from the subgrade level to the natural surface.

That portion of a road where the formation is above the natural surface.

The material placed in an embankment.

Fill batters The side slopes of material placed in an embankment; the degree of such slope is expressed as a ratio of x horizontal to 1 vertical.

Fissility The property of splitting easily along closely spaced parallel planes, such as bedding in shale or cleavage in schist.

Flexible pavement A road pavement that obtains its load spreading properties by inter-granular pressure, mechanical interlock and cohesion between particles of the pavement material. Generally, it is any pavement other than a portland cement pavement.

Fluvial Pertaining to rivers.

Footing The widening at the base of a structure to spread the load to the foundation material.

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Term Meaning

Formation The surface of the finished earthworks, excluding cut or fill batters.

The earthworks structure including all foundation and structural treatments on which the road pavement will be constructed.

Foundation The soil or rock upon which a structure rests.

Friction pile A pile that carries an axial load by the friction developed between the pile and surrounding ground.

Geotextile (filter fabric, geofabric) A synthetic cloth used for various purposes including embankment reinforcing and stabilisation, as a filter layer between dissimilar materials and as a strain absorbing membrane between paving layers.

Geotechnical Site Investigation The process of evaluating the geotechnical character of a site in the context of existing or proposed works or land usage. It may include one or more of the following: evaluation of the geology and hydrogeology of the site; examination of existing geotechnical information pertaining to the site; excavating or boring in soil or rock; in situ assessment, geotechnical properties of materials; recovery of samples of soil or rock for examination, identification, recording, testing or display; testing of soil or rock samples to quantify properties relevant to the purpose of the investigation; and/or reporting of the results.

GDR Geotechnical Design Report.

GIR Geotechnical Investigation Report.

Gravel A mixture of mineral particles occurring in natural deposits, usually passing a 75 millimetres sieve and with a substantial portion retained on a 4.75 millimetres sieve.

Groundwater Subsurface water stored in pores of soil or rocks.

The water below the water table.

HPG Horizontal Profile Gauge.

Indurated Said of a soil or rock hardened or consolidated by pressure, cementation or heat.

Interbedded Said of beds lying between or alternating with others of different character, especially said of rock material laid down in sequence between other beds.

Internal friction angle Shear strength parameter of a soil representing the angle of shearing resistance.

Internal settlement Compression of the constructed embankment.

Iron pyrite Or fool's gold, mineral composed of iron sulphide, FeS2, the most common sulphide mineral.

kPa Kilopascal (kN/m2 or kilonewtons per square metre). A unit of pressure equal to 1,000 Pascals.

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Term Meaning

Landslide Downslope movements of soil or rock masses that occur as a result of shear failure at the boundaries of the moving mass.

Leachate Water containing dissolved soluble substances from rock or soil.

Linear shrinkage The percentage decrease in length of a soil sample in a mould when oven dried from the liquid limit state.

Liquid limit See Atterberg limit(s).

Logging The systematic recording of observable, as opposed to interpreted, data from a site investigation exposure; commonly the data is recorded graphically against depth of hole or length of trench, where it is recorded on pro-forma sheets. However, logging also refers to systematic recording in written form.

Matrix The soil or rock in which something such as a fossil, crystal, or mineral is embedded.

Maximum dry density (MDD) The greatest dry density of a soil obtained when it is compacted in a specified manner over a full range of moisture content. The moisture content at which this density is reached is called the optimum moisture content. Two amounts of compactive effort are commonly specified, referred to as standard and modified.

Metagreywacke Metamorphosed (altered) version of greywacke due to the influence of pressure and/or heating.

Metamorphism The mineralogical, chemical and structural adjustment of solid rocks to physical and chemical conditions imposed at depth below the surface zones of weathering and cementation, which differ from the conditions under which the rocks originated.

Moisture content (water content) The quantity of water that can be removed from a material by heating to 105° Celsius until no further significant change in a mass occurs; usually expressed as a percentage of the dry mass.

NATA National Association of Testing Authorities Australia.

NMLC Triple Tube Core Barrel Rock coring barrel with a diameter of 49.6 millimetres that holds the recovered core in.

NMLC 2 inch (52 millimetres) core.

Non-core drilling

A generic term used to describe the method of advancing a borehole with a rotary bit and with the removal of cuttings by the circulation of a fluid; and in which the full face of the hole is removed by the cutting action of the bit and the cuttings are carried to the surface by the circulation fluid where they can be separated and examined.

NB Northbound.

Optimum moisture content That moisture content of a soil at which a specified amount of compaction will produce the maximum dry density under specified test conditions.

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Term Meaning

Outcrop The exposure, at the surface, of a material (usually rock) differing from its surroundings.

Overburden The soil or other mineral matter which has to be removed to gain access to the underlying material.

Particle size distribution (grading) The quantities of the various particle sizes present in a soil or other material, expressed as a percentage of the whole.

Passive pressure The upper limit of the lateral resistance of soil on a face of a wall, which is attained when the wall compresses the soil in front of it in a horizontal direction.

Pavement The portion of a carriageway above the subgrade (generally natural material) for the support of, and to form a running surface for, vehicular traffic.

Penetration test A test carried out with a standard instrument to determine the load bearing capacity of soil.

Permeability The property of a material by virtue of which a fluid such as water can pass through it.

Phreatic surface Upper zone of saturation in the water table.

Phyllite A cleaved metamorphic rock having affinities with both slates and mica schists. They are formed by low temperature regional metamorphism.

Pier A part of the substructure which supports the super-structure at ends of span and which transfers loads on the superstructure of the foundations.

Piezocone A method of assessing the in situ materials and their strength properties by measuring the penetration resistance of an electronically instrumented cone and sleeve apparatus – see CPTU.

Piezometer A method of measuring groundwater levels; and a dedicated bore for measuring groundwater levels.

Pile A slender member driven, jetted, screwed or formed in the ground to resist loads or thrust.

Pile cap The structural member connecting and distributing load to a group of piles.

Plasticity index The numerical difference between the value of the liquid limit and the value of the plastic limit of a soil.

Pore Pressure Ratio, ru The ratio of the water pressure u to the overburden pressure γh at any point i.e. ru = u/γh=hwδw/γh.

POCAS Peroxide Oxidation Combined Acidity and Sulphate.

Point Load Index Strength (Is(50)) Test

Method of assessing rock strength by crushing core samples in a specialised test apparatus. Is(50) can be correlated with UCS.

Pore water pressure The pressure of the water in the voids of a soil.

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Term Meaning

QRE Quantitative Risk Estimation.

Quartz Crystalline silica (Si02), an important rock forming mineral. It is the commonest gangue (waste) mineral of ore deposits, forms the major largest proportion of most sands;, and has a wide distribution in igneous (especially granitic), metamorphic and sedimentary rocks.

Quartzite A hard, often angular in outcrop, metamorphic rock variable in colour produced by the metamorphism of sandstone.

Quaternary sediments Sediments deposited during the geological period of time from two million years ago to the present.

ru see Pore Pressure Ratio.

Residual Settlement Remaining Primary Consolidation Settlement following removal of surcharge.

Residual soil Soil that has been formed in situ by the chemical weathering of parent rock. When mature, the original structure and fabric of the parent rock are not visible. If original structure and fabric are visible, it is described as an extremely weathered material with soil properties.

Rotary drilling A generic term used to describe the method of advancing a borehole with a rotary bit and with the removal of cuttings by the circulation of a fluid. Rotary drilling may commence from the surface or may be a continuation in rock of a hole drilled through soil by other methods (for example, auger, cable tool).

RQD The ratio of sound (that is, low strength or better) core in lengths of greater than 100 millimetres to the total length of the core, expressed in percent. If the core is broken by handling or by the drilling process (that is, the fracture surfaces are fresh, irregular breaks rather than joint surfaces) the fresh broken pieces are fitted together and counted as one piece.

Residual strength The shear strength of pre-sheared material.

Retaining wall A wall constructed to resist lateral pressure from the adjoining ground, or to maintain in position a mass of earth.

Rigid pavement A pavement of portland cement concrete.

RTA Roads and Traffic Authority of NSW.

Sand Natural mineral particles which will pass through a defined sieve (normally 4.75 millimetres or 2.36 millimetres) and which are free of appreciable quantities of clay and silt.

Scour The erosion of a material by the action of flowing water.

Seismic Refraction Survey Method of determining general soil and rock types based on the refraction of seismic waves as they cross the boundaries between different materials.

SMZ Select Material Zone.

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Term Meaning

Seismic velocity The rate of propagation of an elastic wave through a rock mass, usually measured in kilometres per second. The wave velocity depends on the type of wave, as well as the material through which it travels.

Settlement A downward movement of the soil or of the structure it supports (see also differential settlement).

Shear/crushed zones Zone along which movement has occurred within the rock mass which has resulted in shearing or crushing of the surrounding rock.

Silt All alluvial material intermediate in particle size between sand and clay. It is usually non-plastic.

Site investigation The examination of all those characteristics of a site that might affect the planning, design, construction and operation, or performance of any engineering works on the site. Site investigation is not limited to determining subsurface condition but includes consideration of other aspects such as access, drainage, liability to flooding, availability of public utility services and construction materials.

Skin friction The resistance of the ground surrounding a pile or caisson to its longitudinal movement.

Slope The inclination of a surface with respect to the horizontal, expressed as rise or fall in a certain longitudinal distance.

An inclined surface.

Soil (earth) That part of the upper weathered layer of the earth’s crust which can support plant growth.

Any naturally occurring loose or soft deposit forming part of the earth’s crust and resulting from weathering or breakdown of rock formation or from the decay of vegetation.

Soil profile The profile of soil encountered below the natural ground surface.

SB Southbound.

Spos Peroxide Oxidisable Sulphur.

Stabilising Agent Quicklime, hydrated lime, slag/lime blend, cement.

Standard Penetration Test (SPT) A standard split spoon sampler, about 50 millimetres in diameter, is driven into the ground by blows from a drop hammer weighing 64 kilograms and falling 0.76 metres. The sampler is driven 0.15 metres into the soil at the bottom for a borehole, and the number of blows (N) required to drive it a further 0.3 metres is then recorded. Although the test is entirely empirical, considerable experience with its use has enabled a reasonably reliable correlation to be established between the N value and certain soil properties.

Subgrade The trimmed or prepared portion of the formation on which the pavement is constructed.

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Term Meaning

Subgrade Reaction Modulus (k) Modulus used for simulating elastic soil properties for use in structural design.

Subsurface profile The profile of soil and rock encountered below the natural ground surface.

Talus or scree (type or subset of Colluvium)

Accumulation of rock fragments, usually at the toe of a steep slope or cliff. Fine particles are often worked or winnowed from the deposit.

“TC” bit refusal The depth below the ground surface at which effective refusal occurs when using a “TC” (Tungsten Carbide) faced bit.

Test pit (test rolling) An excavation for the purpose of exposing and sampling soil or rock conditions; the excavation is usually deeper than it is wide.

Toe The part of the base of a retaining wall which is on the side remote from the retained material.

The tip of a pile.

The base of an earthen slope.

Topsoil Surface soil that, which is reasonably free from subsoil, refuse, clay lumps and stones.

Trench An excavation for the purpose of exposing and sampling soil or rock conditions; the excavation is usually longer than it is wide.

Triaxial test A test to determine the stress-strain properties of a pavement material: in which a cylindrical specimen of the material is subjected to a 3- dimensional stress system, and the axial strain is related to the applied stress.

U/D Tube Metal tube, usually 50 millimetres or 75 millimetres diameter, sharpened at one end around its perimeter, used for undisturbed sampling. The tube is used to extract soil samples in a relatively undisturbed state, by being pushed into the soil to be sampled.

Uniaxial Compressive Strength (UCS)

The strength of a material determined in a triaxial test apparatus when the confining pressure is zero, i.e. unconfined.

UZF Upper Zone of Formation.

“V” bit refusal The depth below the ground surface at which effective refusal occurs when using a “V” shaped bit.

Voids The spaces within the bulk of material not occupied by solid matter.

Voids content The ratio of the volume of voids to the total volume of the material, expressed as a percentage.

Voids ratio The ratio of the volume of voids to the solid volume of a material.

Water table The natural level at which water stands in a bore-hole, well, or other depression, under conditions of equilibrium.

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Term Meaning

Wick drains Vertical drains inserted into a soil to aid in groundwater removal.

2:1 etc Refers to the level of gradient (i.e. in this example for two horizontal units, the slope moves one vertical unit).

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Introduction Technical Paper 11

1. Introduction

1.1 Overview

The Roads and Traffic Authority (RTA) proposes to upgrade the Pacific Highway at Bulahdelah. The technical paper forms part of an environmental impact statement (EIS) that defines the proposal and examines its impacts. The Environmental Impact Statement comprises a main volume and 16 technical papers, which are listed below:

Technical Paper 1 Community and Stakeholder Involvement

Technical Paper 2 Statutory Planning

Technical Paper 3 Need and Route Evaluation

Technical Paper 4 The Proposal

Technical Paper 5 Environmental Management Framework

Technical Paper 6 Traffic and Transport

Technical Paper 7 Ecological Assessment and Species Impact Statement

Technical Paper 8 Water

Technical Paper 9 Hazard and Risk

Technical Paper 10 Energy, Waste and Demand on Resources

Technical Paper 11 Topography, Geology and Soils

Technical Paper 12 Visual

Technical Paper 13 Social and Economic

Technical Paper 14 Noise and Vibration

Technical Paper 15 Air

Technical Paper 16 Heritage

The proposed Upgrade of the Pacific Highway at Bulahdelah consists of approximately 8.5 kilometres of dual carriageway that would connect the proposed Karuah to Bulahdelah upgrade to the south to the completed Bulahdelah to Coolongolook upgrade to the north.

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The preferred route, shown in Figure 1.1, passing generally to the east of Bulahdelah, was determined following consideration of a number of options in consultation with the local community and a range of other stakeholders. Connections to the existing highway would be via grade-separated interchanges to the south of Bulahdelah and at Lee Street at the northern end of Bulahdelah township.

The details of the proposal are provided in Technical Paper 4 — The Proposal.

The technical paper addresses topography, geology and soils. Section 2 describes the geotechnical investigations completed for the proposed Upgrade of the Pacific Highway at Bulahdelah including the initial route selection investigations over a broad corridor and subsequent investigations along the preferred route. Section 3 provides an overview of the existing physical setting for the proposal in terms of topography, geology and soils (including acid sulphate soils). Section 4 outlines the key geotechnical characteristics of the proposal including cuttings, embankments, bridge structures, as well as presenting the extent of acid sulphate soil, contaminated soil and erosion and sedimentation impacts and proposed mitigation measures. Section 5 discusses the residual environmental impact of the proposal making allowance for the implementation of the mitigation measures.

The technical paper addresses concerns relevant to the Environmental Impact Statement in relation to the geotechnical issues of topography, geology and soils expected to be encountered during construction of the proposed road. During the detailed design of the Upgrade, further geotechnical investigations would be carried out. The results of the investigation may enable design features such as the cuts to have steeper batters with increased intervals between benches. Investigations during the detail design phase may also result in substantial design changes depending on the construction methods to be adopted. These may also include reducing batter angles and distance between benches.

It is possible that the subsurface soil and rock conditions encountered during detailed design and construction may vary from those identified in this technical paper. It is also noted that groundwater conditions are transient and may vary, particularly after climatic changes. Current access restrictions prevented investigation of subsoil conditions along some sections of the proposed alignment. Should such variations or differences become apparent further geotechnical investigations would be necessary.

Page 1-2 Roads and Traffic Authority 58L320A.070 11 - Topography, Geology & Soils Final.doc

Figure 1.1 The Proposal

Proposed Upgrade

0 2

kilometres

1

Sour

ce: C

adas

tre -

Grea

t Lak

es C

ounc

il 20

00. S

urve

y - Q

asco

200

0.

Golfcourse

Sewagetreatment

plant Wastefacility

Woo

tton

RoadFrys Creek

Waterreservoir

Lee Street

Richmond Street

Stuart Street

Stro

ud S

treet

Craw

ford

Stre

etEx

istin

g Pa

cific

Hig

hway

Markw

ell Road

Caravanpark

Prin

ce S

treet

Alex

andr

a St

reet

Mya

ll St

reet

Bool

oom

bayt

Stre

et

Blanch Street

Meade Street

Church Street

MountainPark

Ann Street

Myall River

Powerline easem

ent

Myall River

Jackson Street

Booral

Road

Existin

g Pacifi

c Highw

ay

Bulahdelah State Forest

Crawford River

Proposed Upgrade

The LakesWay

Frys Creek

Bulahdelah (Alum)Mountain

SEPP 14WetlandNo. 698

Newcastle

Taree

Karuah

Hexham

Coolongolook

Nabiac

Bulahdelah

TuncurryForster

Reconstructionof northboundcarriagewayAccess to

waste facilityand sewage

treatment plant

Northern interchange

Access towater reservoir

Pedestrian Underpass

Pedestrian andvehicle connectionto mountain

Bombah PointRoad Overbridge

Southerninterchange

Realignment ofBooral Road/

Pacific Highwayintersection

Exit toBooral

Road

Pow

erlin

e eas

emen

t

Bombah Point Road

Realignment of Keels Road/Pacific Highway intersection

Realignment ofaccess track forpowerline easement


1.2 Clarification of Government Departments

NSW Department of Primary Industries commenced on 1 July 2004 as the amalgamation of:

NSW Fisheries;

State Forests of NSW;

NSW Agriculture; and

Mineral Resources.

The 16 technical papers supporting the Environment Impact Statement were written before this amalgamation occurred. All references to these government departments in the technical papers signify the NSW Department of Primary Industries.

1.3 Project Description

The proposed Upgrade is the deviation of the Pacific Highway between 92.00 kilometres and 100.40 kilometres north of Newcastle around the township of Bulahdelah, as shown in Figure 1.1. The main components of the project (Figure 1.1) are:

a 210 metre long bridge crossing over the Myall River (approximately between Station 95496 and Station –95706);

two interchanges for connection into Bulahdelah township, from the floodplain south of town and at Lee Street north of the town (approximately at Station 94550 and Station 98500);

bridge overpasses — one on Bombah Point Road and one near the Mountain Park (Station 95950 and Station 96650 respectively);

bridge underpasses — one for pedestrians and wildlife at the continuation of Stuart Street, and one for access to the landfill and sewage treatment plant (Station 97400 and Station 99200 respectively);

bridge over Frys Creek (Station 99700), north bound carriageway only;

cuttings with maximum depth of 24 metres;

fill embankments up to a height of 11 metres;

diversion of existing roads; and

pavements.

The alignment has been divided into five zones that are predominantly cut slopes and four zones that are predominately fill embankments. These zones have been labelled on the basis of cuts (1–5) and fills (1–4) as shown in Table 1.1.


Introduction Technical Paper 11

Table 1.1: Identified Zones

Earthworks

Zone Station (metres)

Total Length (metres) Features

Bridge/ Underpasses/ Overpasses/ Roundabouts

Max. Cut depth (metres)

Max. Fill height (metres)

Fill 1 92000–92600 600 Exit ramp to Booral Road

2.5

Cut 1 92600–93050 450 4

Fill 2

93050–95900 2850 Southern interchange. High embankments on floodplains mainly south of Myall River

Southern interchange bridge Station 94550 Myall River Bridge, Station 95496–95706

11

Cut 2 95900–96600 700 Deep cutting Bombah Point Road overbridge Station 95925

24

Cut 3

96600–96700

100 Bulahdelah Mountain Access Overbridge Station 96650

5

Cut 4

96750–97000

250 Ancient landslide area. Excavation through deep colluvium

13

Fill 3

97000–98000

1000 Partly on colluvium Stuart Street Pedestrian and Wildlife Underpass Station 97380

11

Cut 5

98000–98850

850 Northern interchange

Interchange bridges Station 98450 and 98550

17

98850–100000

1150 Partly on Myall River floodplain over areas of soft alluvium

Underpass to waste facility, Station 99200; Frys Creek Bridge northbound only, Station 99740

Fill 4

100000–100400

400 Tie in to Pacific Highway

5

Total 8350


Geotechnical Investigations Technical Paper 11

2. Geotechnical Investigations

2.1 Investigation Methods

Geotechnical investigation for the project comprised the following activities in the period from 2000 to 2003:

desk top study;

terrain evaluation;

geological mapping;

test pits;

borehole drilling;

installation of piezometers at 20 locations for sampling of groundwater and measurement of groundwater levels;

cone penetration tests (CPT and CPTU);

installation and monitoring of inclinometers to monitor ground movement;

seismic refraction traverses;

environmental assessment and sampling;

laboratory testing (geotechnical and environmental); and

reporting and independent peer review.

2.2 Desk Study

The desk study component of the investigations involved the following activities:

compiling and reviewing existing geological and geotechnical data including topographic, geological and acid sulphate soil risk maps, aerial photographs and soil profile data;

contacting with the Department of Mineral Resources to assess the likely presence of commercial mineral deposits;

contacting NSW Agriculture and the Department of Environment and Conservation (formerly Environment Protection Authority) regarding registration of contaminated sites or potentially contaminating activities within the study area;



contacting Great Lakes Council regarding identification of potential construction materials within the study area;

reviewing geotechnical data from adjacent projects; and

reviewing records of alunite mining.

2.3 Geological Mapping

Geological mapping, was carried out by experienced engineering geologists or geotechnical engineers, and involved walkover surveys of the study area, mapping significant surface features including outcrop and cuttings, mine workings, topography, vegetation and drainage. Existing road cuttings along the Pacific Highway and other exposure of rock were also mapped. The information was used to produce the Geotechnical Terrain Map (Figure 2.1) and the Geological Map (Figure 2.2).

2.4 Subsurface Investigation

The subsurface investigations comprised the drilling of augered and cored boreholes, excavation of test pits, cone penetration tests (CPTs) and seismic refraction transverses. All tests conducted over the entire study corridor and the stage at which they were conducted are provided in Table 2.1.

Table 2.1: Site Investigation Details

Investigation Stage

Boreholes Test Pits Cone Penetration

Tests Seismic

Transverses

Route Selection 30 9 9 6

Preferred Route Investigation

75 73 27 16

Total 105 82 36 22

Fieldwork was supervised by an experienced geotechnical engineer or engineering geologist who was responsible for locating the test pits, boreholes and cone penetration tests; logging, sampling and overseeing in situ tests; and mapping of terrain. The location of the geotechnical investigation sites is shown in Figure 2.3.

Test pits — test pits were excavated using a backhoe to a maximum depth of 3 metres. Bulk samples were collected for laboratory analysis. The pits were backfilled with excavated material on completion. Dynamic Cone Penetrometer (DCP) tests were performed adjacent to most test pits.


CUT

1

FILL 2

CUT

2

FILL3

CCCUUUTTT

555

FILL 4

CCCUUUTTT

444CCCUUU

TTT333

0 2

kilometres

1

Proposed Upgrade

Hill crests and ridges (igneous)

Colluvial soils

Extent of colluvium crossinghighway

Slopes (sedimentary)

Alluvial plains

Wetlands

Fault

Myall syncline

Backswamps and backplains

Figure 2.1 Geotechnical Terrain

Golfcourse

Sewagetreatment

plant Wastefacility

Woo

tton

RoadFrys Creek

Pow

erlin

e eas

emen

t

Lee Street

Richmond Street

Stuart Street

Stro

ud S

treet

Craw

ford

Stre

etEx

istin

g Pa

cific

Hig

hway

Markw

ell Road

Caravanpark

Prin

ce S

treet

Alex

andr

a St

reet

Mya

ll St

reet

Bool

oom

bayt

Stre

et

Blanch Street

Meade Street

Church StreetAnn Street

Bombah PointRoad

Myall River

Powerline easem

ent

Myall River

Jackson Street

Booral

Road

Existin

g Pacifi

c Highw

ay


Crawfor

d

River

Proposed Upgrade

The LakesWay

Frys Creek


FILL 1

Sour

ce: C

adas

tre -

Grea

t Lak

es C

ounc

il 20

00. S

urve

y - Q

asco

200

0.


MountainPark

Waterreservoir

Approximate extentof Colluvium

0 2

kilometres

1

Proposed Upgrade

Alum Mountain volcanics –Sams Road rhyolite member

Alum Mountain volcanics –Burdekins cap basalt member

Koolanock sandstone

Bulahdelah formation

Undifferentiated quaternaryalluvium

Undifferentiated colluvial soils

Fault

Myall syncline

Inferred faults

Figure 2.2 Geological Map

Sour

ce: C

adas

tre -

Grea

t Lak

es C

ounc

il 20

00. S

urve

y - Q

asco

200

0.

CUT

1

FILL 2

CUT

2

FILL3

CCCUUUTTT

555

FILL 4

CUT

CUT

CUT 333

CUT

CUT

CUT 444

MountainPark


Golfcourse

Sewagetreatment

plant Wastefacility

Woo

tton

RoadFrys Creek

Pow

erlin

e eas

emen

t

Waterreservoir

Lee Street

Richmond Street

Stuart Street

Stro

ud S

treet

Craw

ford

Stre

etEx

istin

g Pa

cific

Hig

hway

Markw

ell Road

Caravanpark

Prin

ce S

treet

Alex

andr

a St

reet

Mya

ll St

reet

Bool

oom

bayt

Stre

et

Blanch Street

Meade Street

Church StreetAnn Street

Bombah PointRoad

Myall River

Powerline easem

ent

Myall River

Jackson Street

Booral

Road

Existin

g Pacifi

c Highw

ay


Crawfor

d R

iver

Proposed Upgrade

The LakesWay

Frys Creek


FILL 1

Approximate extentof Colluvium

Existing Pacific Highway

Bom

bah

Point

Roa

d

Ann Street

Myall River

To a

nd fr

om K

arua

h


Booral Road

Figure 2.3a GeotechnicalInvestigation Test Sites

A B

From Karuah


Existi

ng Pa

cific H

ighway

Booral

Road

Exist

ing P

acific

High

way Bombah Point Road

Transmission Easem

ent

Ann Street

Church Street

Craw

ford

Stre

et Mountain ParkBulahdelah

Central School

CourtHouse

Myall River

Proposed newbridge crossing

Meades Street

Blanch Street

Mac

kenz

ie S

treet

Exis

ting

Paci

fic H

ighw

ay

Tran

smis

sion

Eas

emen

t

Stuart Street

Richmond Street

Bool

oom

bayt

Stre

et

WaterReservoir

ProposedAccess Track


Lee Street

Exist

ing

Paci

fic H

ighw

ay

CaravanPark

Golf Course

Golf Course

Existing Pacific

Highway

WasteDepot

Frys Creek

Trans

mission

Ease

ment

To Taree

Woo

ton

Road

Mya

ll Rive

r

A

B

C

D

Join

s m

ap B

Joins map C

Join

s m

ap A

0 1.0

kilometres

0.5

1: 12000 approx

Aeria

l pho

to ta

ken

26 F

ebru

ary

2000

. Pro

perty

bou

ndar

y su

pplie

d by

Gre

at L

akes

Cou

ncil.

Borehole

Inclined borehole

Borehole with Piezometer

Borehole with Inclinometer

Testpit

Cone penetration test

BH

BH

BH

BH

CPT

TP TP

CPT

BH

Proposed Upgrade cut

Proposed Upgrade fill

Seismic geophysical line

Borehole - Route Selection Report

Testpit - Route Selection Report

Cone penetration test - Route Selection Report

93800

93700

93600

93500

93400

93300

93200

93100

93000

92900

92800

92700

92600

92500

92400

92300

92200

92100

92000

9630

096

200

96100

96000

95900

95800

95700

95600

95500

95400

95300

95200

95100

95000

94900

94800

94700

94600

94500

94400

94300

94200

94100

94000

93900

93800

93700

9360

0

9350

0

0096

200

96100

96000

95900

FILL

2FI

LL 2

FILL

2

FILL 2

FILL 2

FILL 2

CUT 2

CUT 2

CUT 2

FILL

FILL

FILL

2 2 2

CU

TC

UT

CU

T 111

FIL

LFIL

LFIL

L 111

95800

95700

95600

95500

95400

95300

95200

95100

95000

94900

800

0

0

0

300

94200

94100

94000

93900

93800

93700

9360

0

9350

0

FILL

2FI

LL 2

FILL

2

FILL 2

FILL 2

FILL 2

0

0

FIL

LFIL

L 11

93000

00

CU

TC

UT

CU

T 111

Existing Pac 00

93700

93600

93500

93400

93300

93200

00

FILL

FILL

FILL

2 2 2

CPT

BH

BH

TP

TP

TP

TP

CPT

BH

CPT

CPTBH

CPT

TP

CPT

CPT

CPT

CPT

TP

BH

TP

BH

BH

TP

BHCPT

BHTP

CPTCPT

CPT

CPT

BH

CPTBH

CPT

TPTP

TP BH

TPTP

BH

TP TP

BH

TP

BH

BH

Waterreservoir

Lee

Stre

et


Caravanpark

Golf course

Exis

ting

Paci

fic H

ighw

ay

Wastefacility

Frys Creek

Pow

erlin

e ea

sem

ent

Wootton Road

98600

98800

98700

98500

98400

98300

98200

98100

98000

99600

99500

99400

99300

99200

99100

99000

98900

100300

100200

100100

100000

99900

99800

99700

100500

100400

Pacif

ic Hi

ghw

ay

Powerline easem

ent

Ann Street

Church Street

Mountain ParkBulahdelah

Central School

Meade Street

Blanch Street

Mac

kenz

ie S

treet

Exis

ting

Paci

fic H

ighw

ay

Pow

erlin

e ea

sem

ent

Stuart Street

Richmond Street

Bool

oom

bayt

Stre

et

Waterreservoir

Proposedaccess track


Lee StreetEx

isting

Caravanpark

Haro

ld S

treet

BulahdelahState Forest

St JosephsPrimary School

0 1.0

kilometres

0.5

1: 12000 approx

Map C Map D

From Karuah


Existi

ng Pa

cific H

ighway

Booral

Road

Exist

ing P

acific

High

way Bombah Point Road

Transmission Easem

ent

Ann Street

Church Street

Craw

ford

Stre

et Mountain ParkBulahdelah

Central School

CourtHouse

Myall River

Proposed newbridge crossing

Meades Street

Blanch Street

Mac

kenz

ie S

treet

Exis

ting

Paci

fic H

ighw

ay

Tran

smis

sion

Eas

emen

t

Stuart Street

Richmond Street

Bool

oom

bayt

Stre

et

WaterReservoir

ProposedAccess Track


Lee Street

Exist

ing

Paci

fic H

ighw

ay

CaravanPark

Golf Course

Golf Course

Existing Pacific

Highway

WasteDepot

Frys Creek

Trans

mission

Ease

ment

To Taree

Woo

ton

Road

Mya

ll Rive

r

D

C

BA

Join

s m

ap C

Joins map B

Joins map D

Aeria

l pho

to ta

ken

26 F

ebru

ary

2000

. Pro

perty

bou

ndar

y su

pplie

d by

Gre

at L

akes

Cou

ncil

Figure 2.3b GeotechnicalInvestigation Test Sites

Borehole

Inclined borehole

Borehole with Piezometer

Borehole with Inclinometer

Testpit

Cone penetration test

BH

BH

BH

BH

CPT

TP TP

CPT

BH

Proposed Upgrade cut

Proposed Upgrade fill

Seismic geophysical line

Borehole - Route Selection Report

Testpit - Route Selection Report

Cone penetration test - Route Selection Report

Powerline

rk

Stre

et


Caravanpark

98600

00

98500

98400

98300

98200

98100

0

Exis

ting

Paci

fic H

ighw

ay

0

00

8900

100000

99900

99800

00

TP

TP

TP TP

BH

BH

BH

TP

TP

BH

TP

BH

BHTP

BH

BH

BHBHBHBH

BH

BH

TP

BH

BH

BH BH

BHBH

TP

BH

TP

TP

TP

BH

TP

BH

BHTP

BH

BH

TP

BH

BH

BH

BH

BHTP

BH

BHTPBH

TPBH

TPBH

TP

TP

TP

TP

BH

BH

TP

BH

TP

BH

CCCU

T

UT

UT 222

FillFillFill 2 2 2

CCCU

TU

TU

T 333

CU

T

CU

T

CU

T 444

FIL

LFIL

LFIL

L 333

CU

T 5

CU

T 5

CU

T 5

FILL 4FILL 4FILL 4

CU

TC

UT

CU

T 5 5 5


Boreholes — Vertical and inclined boreholes were drilled using different types of truck mounted drill rigs, depending on access constraints. The boreholes were advanced through the overburden soils using V-shaped bit or TC (Tungsten Carbide) bit to depths of 8–28 metres with in situ standard penetration testing (SPT) at regular intervals to assess the soil consistency or strength. Undisturbed soil samples were recovered at selected depths for identification and laboratory tests including triaxial and direct shear strength tests.

Boreholes were advanced through rock using NMLC rotary coring techniques with a diamond-tipped drill bit. Point load strength tests were performed at regular intervals along the core where appropriate. Selected samples of core were tested in the laboratory for Uniaxial Compressive Strength (UCS).

Piezometers were installed in 20 boreholes to monitor groundwater levels. All remaining boreholes were backfilled upon completion with cement/ bentonite grout. Inclinometers were installed in two boreholes in the colluvium area.

Cone Penetration Tests — Cone Penetration Tests with pore pressure measurements were performed to a maximum depth of 25 metres. In situ pore pressure dissipation tests were performed during the Cone Penetration Tests at selected depths to assess soil permeability and consolidation characteristics.

Seismic Traverses — Seismic refraction surveys were carried out across the site to assess layering within the alluvium and the depth to rock on the alluvial floodplains and at cut locations, and assist in assessment of the rippability of the material at cutting sites. During the preferred route investigation, seismic testing was carried out along and transverse to the proposed alignment in areas of proposed cut.

Test locations were selected to provide coverage of each of the geotechnical terrain units identified within the study area (where access permitted), with a particular focus on the nominated route options.

2.5 Soil Contamination Sampling

The soil sampling for the contamination assessment targeted potential land use activities identified in the desk study. The location of sites tested for contamination is shown ion Figure 2.4.

Soil samples were collected from boreholes, test pits and hand auger holes. All samples collected from test pits or from deeper boreholes (deeper than 0.2 metres) were collected for background analysis purposes.

For all surface soil samples, and where the potential for hydrocarbon contaminants was possible, field Photo-ionisation Detector (PID) screening was conducted. Field quality control procedures performed for this investigation included the use of standard field sampling sheets and, the use of calibrated monitoring equipment, and the collection of field duplicate samples.


Golfcourse

Sewagetreatment

plant Wastefacility

Woo

tton

RoadFrys Creek

Pow

erlin

e eas

emen

t

Waterreservoir

Lee Street

Richmond Street

Stuart Street

Stro

ud S

treet

Craw

ford

Stre

etEx

istin

g Pa

cific

Hig

hway

Markw

ell Road

Caravanpark

Prin

ce S

treet

Alex

andr

a St

reet

Mya

ll St

reet

Bool

oom

bayt

Stre

et

Blanch Street

Meade Street

Church Street

MountainPark

Ann Street

Bombah PointRoad

Myall River

Powerline easem

ent

Myall River

Jackson Street

Booral

Road

Existin

g Pacifi

c Highw

ay


Crawfor

d Rive

r

Proposed Upgrade

The LakesWay

Frys Creek



Proposed Upgrade

Wastewatertreatment plant

Alunite Mine

Saw mill

0 2

kilometres

1Figure 2.4 Contaminated Lands Investigation

Test Sites

Sour

ce: C

adas

tre -

Grea

t Lak

es C

ounc

il 20

00. S

urve

y - Q

asco

200

0.

Contaminated lands investigation sites


2.6 Acid Sulphate Soil and Rock Sampling

Prior to carrying out fieldwork, the desk top study identified areas of high probability of potential or actual acid sulphate soils (PASS or AASS) within the first 3 metres of the soil profile. This identification was carried out with reference to the Bulahdelah Acid Sulphate Soils Risk Map (Department of Land and Water Conservation 1997). The location of some of the test pits and hand auger boreholes were then chosen to target these areas. Field indicator tests (pH and peroxide tests) were performed on each field sample to identify the presence of actual or potential acid sulphate soils. These field test results were treated as indicators only to be confirmed by laboratory analysis.

Samples of rock for assessing acid generation potential were taken from rock cores at borehole locations across the study area. The borehole locations were selected so that each of the main rock types from the study area were analysed.

The extent of potential acid sulphate soils is illustrated on Figure 2.5.



Proposed Upgrade

Potential acid sulphate soils

0 2

kilometres

1Figure 2.5 Acid Sulphate Soils Risk Map

Golfcourse

Sewagetreatment

plant Wastefacility

Woo

tton

RoadFrys Creek

Pow

erlin

e eas

emen

t

Waterreservoir

Lee Street

Richmond Street

Stuart Street

Stro

ud S

treet

Craw

ford

Stre

etEx

istin

g Pa

cific

Hig

hway

Markw

ell Road

Caravanpark

Prin

ce S

treet

Alex

andr

a St

reet

Mya

ll St

reet

Bool

oom

bayt

Stre

et

Blanch Street

Meade Street

Church Street

MountainPark

Ann Street

Bombah PointRoad

Myall River

Powerline easem

ent

Myall River

Jackson Street

Booral

Road

Existin

g Pacifi

c Highw

ay


Crawfor

d Rive

r

Proposed Upgrade

The LakesWay

Frys Creek



2.7 Laboratory Testing

2.7.1 Geotechnical Testing

Representative samples of the subsurface profile were recovered from the test pits and boreholes. Selected samples were tested in NATA registered laboratories as summarised in Table 2.2:

Table 2.2: Summary of Laboratory Testing

Test Property Method No. of Tests

Moisture content Field Gravimetric Moisture AS1289 2.1.1/RTA T120 129

Particle grading Particle size distribution AS1289 3.6.1/RTA T106 74

Particle size distribution – hydrometer

Particle size distribution RTA T107

Atterberg limits Liquid and plastic limit, plasticity index,

AS1289 3.1.1, 3.2.1, 3.3.1, RTA T103, T108 & T109 & RTA 30511.

71

Linear shrinkage Linear shrinkage RTA T113 7

Compaction (standard)

Optimum moisture content, maximum dry density

RTA T111, AS1289 5.1.1 23

Soaked CBR California bearing ratio RTA T117, AS1289 F1.1 23

1D Consolidation - oedometer

Coefficients of consolidation, volume compressibility, permeability, recompression and compression index

AS1289 6.6.1 4

Triaxial (consolidated undrained)

Undrained shear strength AS1289.6.2.2 7

Direct shear box Cohesion, peak and residual angle of internal friction

AS1289.6.4.2 7

Emerson Dispersion Emerson dispersion class AS1289 3.8.1 24

Shear Vane test Soil strength As per manufacturer’s instructions

–-

Uniaxial compressive strength, soil

Soil strength ASTM D2166 7

Point load strength index, rock

Rock strength AS4133 4.1 57

Uniaxial Compressive Strength, rock

Rock strength AS4122.4.2; RTA T229 26



Table 2.2 continued

Test Property Method No. of Tests

X-ray Diffraction Semi-quantitative clay mineralogy

- 15

Petrographic Analysis Microscopic description - 21

1. RTA specification 3051 relates to requirements for subgrade materials and does not apply to all materials tested.

2. Refer to laboratory tests reports for details in regards to sample pre-treatment.

2.7.2 Soil Contamination Testing

Based on the results of the desktop study, sampling and analysis plan, field observations and photo-ionisation detector (PID) screening results, samples were analysed for substances selected from the following list:

total petroleum hydrocarbons, benzene, toluene, ethyl benzene, and total xylenes;

polycyclic aromatic hydrocarbons;

organochlorine pesticides;

organophosphorus pesticides;

heavy metals;

total phenolics; and

nutrients

2.7.3 Acid Sulphate Soil Testing

To confirm the field indicator test results, soil samples were submitted for laboratory peroxide oxidation combined acidity and sulphate testing.

2.7.4 Acid Sulphate Rock Testing

Rock samples were submitted for laboratory analysis, which involved net acid producing potential, acid neutralising capacity and net acid generation testing on pulverised samples.



2.8 Reporting

A number of reports prepared by Parsons Brinckerhoff throughout the route selection and refinement of the proposed Upgrade are summarised below.

Pacific Highway Upgrade, Bulahdelah — Geotechnical Investigation for Route Selection (August 2001).

A route selection geotechnical investigation was carried out across a broad study area to assist in the selection of the most suitable route for the Upgrade of the Pacific Highway at Bulahdelah. Activities included geological mapping, subsurface investigation, soil contamination sampling, acid sulphate soil and rock sampling. The report describes the geotechnical characteristics of the study area with a particular focus on five nominated route options.

Acid Sulphate Soil Investigation and Management Plan, Pacific Highway Upgrade, Bulahdelah (July 2002).

A preliminary investigation identified areas in the vicinity of the Myall River as having a high probability of acid sulphate soil (ASS) occurrence. The delineation of the extent of ASS and preparation of an ASS management plan was recommended. This report presents the supplementary investigation carried out in the vicinity of the Myall River as well as an ASS management plan for construction in this area.

Bulahdelah Upgrade, Interim Batter Report for Preferred Route — Draft (August 2002).

Concept design drawings indicated proposed cuts up to 25 metres in height and the likelihood of a colluvial slope over a 400 metres length of the preferred route at the foot of Bulahdelah (Alum) Mountain. Many large irregular shaped boulders up to 5 metres across are located on the slopes of the Bulahdelah (Alum) Mountain upslope of the preferred road alignment. The size and location of these boulders were considered to present a potential hazard to the proposed road below. This report provides preliminary comments and analyses for cut batter slopes along the proposed route alignment.

Bulahdelah Upgrade, Interim Report on Fill Zones for Preferred Route (Contract E/01/06) (October 2002).

The proposed route alignment, as shown in (Refer to Figure 1.1), comprises has four zones of fill embankment along the main carriageway and fill embankments associated with two interchanges. Concept design longitudinal sections show that the fill embankments proposed across the alluvial plains would be up to 11 metres in height. This report provides preliminary assessment of settlement and stability for embankments along the preferred route. It primarily concentrates on the fill embankments proposed across the Myall River floodplain, particularly at the bridge abutments.



Bulahdelah Upgrade, Geology of Northern Interchange (November 2002).

This report presents a preliminary interpretation of the geology at the proposed northern interchange based on field mapping, boreholes, test pits and seismic refraction information.

Pacific Highway Upgrade — Bulahdelah Geotechnical Investigation Report for Preferred Route (December 2002).

This report presents the findings of the preferred route geotechnical investigations. It includes the results of the above two interim reports and addresses batter and fill issues.

Bulahdelah Upgrade of Pacific Highway: Report on Colluvium Area (Cut 4) Stability (February 2003) and Bulahdelah Upgrade of Pacific Highway — Report on Colluvium Area Stability (January 2004).

Early geotechnical investigations for the preferred Route Option E along the lower western slopes of Bulahdelah (Alum) Mountain indicated that the colluvium area was more extensive than estimated during the route selection stage. The area was investigated further by additional boreholes, laboratory testing and seismic traverses. This report summarises the findings of the additional investigation and assesses the stability of the colluvium area in its current state and for the proposed alignment.

Contamination Assessment, Former Alunite Mine, Sawmill and Wastewater Treatment Plant, Bulahdelah (March 2003).

Contaminated soil surveys were undertaken at the former alunite mine, decommissioned sawmill and decommissioned sewage treatment plant located along the preferred route. The objective of the contamination assessment was to identify potential soil contamination issues occurring as a result of past or present site activities.


Physical Setting Technical Paper 11

3. Physical Setting

3.1 Terrain, Topography and Geology

The terrain along the proposed upgrade is shown in Figure 2.1. The alluvial plains, and backswamps and backplains, of the Myall River and the alluvial plains at the northern end of the study corridor are significant in terms of geotechnical constraints on the proposed Upgrade. The ground surface along the proposed alignment rises steeply north of the Myall River then continues along the foot slopes of Bulahdelah (Alum) Mountain, which peaks about 200 metres above the alignment. The foot slopes are generally covered with colluvium and scree from the escarpments along the western side of the mountain. The alignment crosses hill crests and ridges of igneous rock of the Bulahdelah (Alum) Mountain at the northern interchange.

The alluvial plains are generally cleared and used for grazing. The forested foot slopes of Bulahdelah (Alum) Mountain slope about 0–15 degrees, are traversed by minor gullies and streams.

There are four main terrain units within the study area. There are hill crests and ridges (igneous lithology), slopes (sedimentary lithology and colluvium), alluvial plains, and backswamps and backplains. The characteristics of these units are summarised in the following sections.

3.1.1 Hill Crests and Ridges

Topography

The dominant linear ridge, of the hill crests and ridges terrain unit, runs in a north-northeast orientation along the eastern edge and northern edges of the Bulahdelah township. The unit incorporates the crest, cliffs and upper slopes of Bulahdelah (Alum) Mountain to the east of the township, and the crest and upper slope landforms of the knolls and saddle north-west of the Pacific Highway. The slope grades are typically 20–35 percent for the knolls and saddle, and 35–80 percent for Bulahdelah (Alum) Mountain.

Subsurface Conditions

Soils

The soil profile is typically shallow (1.5–2.0 metres), very stiff, dry to moist sandy clay and clay. No free groundwater was encountered in the soil profile.



Rock

The rock is olivine basalt or rhyolite, which is typically distinctly weathered to a depth of 10–15 metres and slightly weathered below that to a drilled investigation depth of 24 metres. The rock strength is typically low to medium where distinctly weathered and high to very high where slightly weathered.

The rock ranges between being slightly fractured to fragmented with joint orientation predominantly sub-horizontal with some sub-vertical joints. Frequent significant weathered zones, clay seams, crushed and shear zones were noted which caused difficulties with drilling.

For example, the geology at the northern interchange is a complex sequence of sedimentary and volcanic rock intersected by faulting.

3.1.2 Slopes

Topography

The slopes terrain unit comprises the mid–lower slopes associated with the hill crest and ridges terrain unit on the eastern edge of the Myall River valley as well as the shallow relief hills on the western edge of the Myall River valley. The slope grades are typically 10–15 percent in the western hills and eastern lower slopes, and 20–35 percent for the eastern mid slopes.


Soils/Colluvium

Test locations typically showed a soil profile that is relatively shallow (1.5–2.5 metres) over sandstone and relatively deep (9–13 metres) over siltstone, except for the Bulahdelah (Alum) Mountain mid-slopes and upper slopes of the western hills where the soil depth over siltstone is typically 3 metres. In areas of the identified colluvium where the depth to rock extended to 25 metres, the colluvium comprises a variety of materials including cobbles and boulders (up to 5 metres maximum size) in a silty clay–sand–gravel matrix considered to be the remnants of an ancient landslide.

It would appear that the siltstone is more susceptible to weathering than the sandstone. The residual soils are moist, stiff to very stiff silty clays, clayey silts and clays. Groundwater was encountered at depths of 3–9 metres within the soil profile during the fieldwork and monitoring period.



Rock

The rock is typically fine to medium grained sandstone and siltstone. The degree of weathering ranges between extremely weathered (0.7–5.0 metres thick) to distinctly weathered (1.5–7.3 metres thick). It is slightly weathered below that to a drilled investigation depth of up to 18 metres.

The siltstone rock strength is typically extremely low to very low where extremely to distinctly weathered and medium strong where slightly weathered. The sandstone rock strength ranges from extremely low where extremely weathered, to low to high where distinctly weathered, to high to very high where slightly weathered.

The siltstone is fragmented to highly fractured where distinctly weathered and fractured to slightly fractured where slightly weathered with some clay seams, crushed zones and joint coating noted. The sandstone is fractured to highly fractured where distinctly weathered and slightly fractured where slightly weathered with frequent clay seams, and crushed and highly fractured zones, and some joint coating and carbonaceous zones noted.

Joint orientations are predominantly sub-vertical on the eastern side of the Myall River and sub-horizontal on the western side of the Myall River.

3.1.3 Alluvial Plains

Topography

This terrain unit comprises the floodplains associated with the Myall and Crawford Rivers, bounded by the lower slopes of Bulahdelah (Alum) Mountain and knolls to the east, and the shallow relief hills to the west. The plains are typically between 3–10 metres above Australian Height Datum (AHD).


Soils

The soils in this terrain unit comprise medium to high plasticity clays and silty clays, silts and sands to approximately 11–13 metres overlying sands and clays to 18–26 metres, which in turn are overlying siltstone and sandstone. The soils are generally more sandy and silty close to the river streams and in the stream levees. The depth of alluvium decreases at the edges of the alluvial valley and is a shallower 10 metres in the vicinity of Frys Creek at the northern end of the study area. Medium to coarse grained gravels were encountered in the upper end of the Myall River stream at a depth of between 12–16 metres.

The clays were generally stiff to very stiff and the silts and sands medium dense. However, very soft clay and very loose silts were encountered at the confluence of the Crawford and Myall Rivers and very loose to loose silts and sand layers were encountered in some profiles throughout the study area. The surface clays to 1 metre are generally soft to firm.



Groundwater was typically first struck between 3 metres and 13 metres. Soil moisture was generally slightly moist to moist above the water table and moist to wet below the water table with measured moisture contents of 22–40 percent.

Rock

The underlying rock was extremely to slightly weathered siltstone and/or sandstone. The depth of rock at the investigation locations was typically between 1.5–2.5 metres. Typical rock strengths were very low to low for extremely weathered rock, low to medium for distinctly weathered, and medium to high for slightly to distinctly weathered.

The underlying rock is from the Bulahdelah formation, which is also encountered within the slopes terrain unit.

3.1.4 Backswamps and Backplains

Topography

The backswamp and backplain landforms that line the Myall and Crawford rivers make up this terrain unit. They are typically contained within the meanders immediately beyond the natural river levees and have a level of less than 3 metres Australian Height Datum.


The subsurface profile is very similar to the alluvial plains terrain unit except for soils being generally moist to wet. Groundwater inflows were noted at the surface ranging down to 3 metres in depth. Surface water ponding was noted in some lower lying areas and topographic depressions..

3.2 Regional Geology

The regional geology, taken from the 1:100 000 Geological Series Sheet 9333 (Edition 1, NSW Department of Mineral Resources 1991) for Bulahdelah, and major structural features noted during field mapping are shown ion Figure 2.2.

The 1:100 000 Geological Series Sheet 9333 Bulahdelah, indicates that the study area is underlain by rock units deformed by the Myall Syncline. The axis of the Myall Syncline, which has also undergone normal faulting, is located approximately 1 kilometre to the west of the Myall River and trends northwest to southeast. Immediately to the east and west of the Myall Syncline axis the Bulahdelah Formation of Middle Permian age, typically contains grey to brown, massive to thickly bedded lithic sandstone with occasional stringers of pebbles, and poorly exposed siltstone and claystone. Immediately east and west of the Myall River, undifferentiated Quaternary alluvium including levee and back swamp deposits overlie the Bulahdelah Formation.



East of the Bulahdelah Formation, the Younging west sequence of the Myall Syncline comprises the Early Permian Alum Mountain Volcanics (Lakes Road Rhyolite Member and the Burdekins Gap Basalt Member), the Late Carboniferous Muirs Creek Conglomerate and the Late Carboniferous Koolanock Sandstone.

The Lakes Road Rhyolite Member of the Alum Mountain Volcanics typically comprises yellow to white spherulitic and fluidal rhyolite with minor albitized and silicified basalt. The Burdekins Gap Basalt Member typically comprises massive crystalline and amygdaloidal alkaline olivine basalt with thin interbeds of conglomerate, lithic sandstone, and minor coal seams.

The Muirs Creek Conglomerate typically comprises massive boulder to cobble conglomerate containing clasts of rhyolite, with thinner interbeds of lithic sandstone, siltstone, carbonaceous shale and tuffaceous sandstone.

The Koolanock Sandstone typically comprises brown to grey lithic sandstone with thin interbeds of bioturbated siltstone, massive lithic sandstone containing up to three cream rhyolite flows and cyclical, upward fining conglomerate, lithic sandstone, carbonaceous siltstone, and minor coal seams.

3.3 Geomorphological Model

Talus and floodplain deposits have been encountered on sections of the preferred route. The landscape is dominated by the volcanic rocks of the Bulahdelah (Alum) Mountain ridge line exposed approximately 1 kilometre east of the Bulahdelah township. The mountain rises nearly 300 metres from the valley floor with extensive vertical rock cliffs exposed at the ridge. Colluvial soils deposited under gravity forces, aided by water flow, are exposed downslope of the ridge line. West of these colluvial scree slopes the Bulahdelah township is founded largely on residual soils overlying sandstones, siltstones and claystones of the Bulahdelah Formation.

East and west of the Myall River, the rocks of the Bulahdelah Formation are overlain by Undifferentiated Quaternary alluvium including levee and back swamp deposits, and possible palaeochannels associated with the Myall River flowing east towards the coast.


Geotechnical Characteristics of the Proposed Route Technical Paper 11

4. Geotechnical Characteristics of the Proposed Route

4.1 Interpreted Subsurface Conditions

The interpreted subsurface conditions within each of the identified zones at the test locations are described below.

4.1.1 Fill 1

The proposed fill embankment is located on the edge of the alluvial plains of the Myall River on a similar alignment to the existing Pacific Highway. The maximum proposed embankment height along this section is approximately 2.5 metres. The upgrade section is partly over existing fill and partly new fill over natural ground as the road diverges from the existing highway.

Field investigations within the proposed embankment footprint encountered fill overlying alluvial soils. The soil profile is broadly summarised in 4.1. No free groundwater was encountered in the test pits at the time of the investigation.

Table 4.1: Fill 1 Soil Profile

Unit Depth (metres)

Thickness (metres)

Description

Fill: 0 0.75–1.1 Sandy gravel, medium to coarse grained, grey/brown, dense to very dense (existing Pacific Highway embankment).

Alluvium: 0.75–1.1 >0.6 Sandy silt to silty clay, medium plasticity, brown to dark grey, stiff to very stiff.

4.1.2 Cut 1

This shallow box cut (4 metres deep) is through a low ridge at the southern end of the proposed Upgrade.

Field investigations encountered residual soils overlying rock units of the Bulahdelah Formation. The inferred profile is summarised in Table 4.2. No free groundwater was encountered in the boreholes or the test pits at the time of the investigation.



Table 4.2: Cut 1 Inferred Profile

Unit Depth (metres)

Thickness (metres)

Description

Topsoil 0 0–0.5 Sandy silt, light brown

Residual 0–0.5 ≈ 2.4 Silty clay with some sand and gravel, medium plasticity, very stiff or hard.

Bulahdelah Formation

> ≈ 2.4 –- Siltstone, extremely weathered, extremely low strength, interbedded with bands of moderately to highly weathered, very low strength siltstone, highly fractured.

4.1.3 Fill 2

The proposed fill embankment crosses the alluvial plains of the Myall River including areas previously reported as backswamps and backplains. The Fill is predominately on the southern side of the Myall River but continues to the north for a short length. The maximum proposed embankment height along this section is approximately 11 metres for the approaches to the proposed southern interchange and 10 metres at the proposed bridge across the Myall River (Station 95560–95700).

Field investigations encountered highly variable ground conditions across this floodplain area. These comprised a surface layer of topsoil overlying alluvium with interbedded horizons of clays, silts and sands of variable strength and consistency. Residual soil overlies sandstone or siltstone bedrock. The ground profile is summarised in Table 4.3.

Table 4.3: Fill 2 Ground Profile

Unit Depth (metres)

Thickness (metres)

Description

Topsoil: 0 0–0.5 Sandy silt or silty clay, dark brown.

Alluvium 1: 0–0.5 1.1–9.3 Silty clay, medium to high plasticity, dark brown to grey, soft (very soft adjacent to Myall River) to very stiff.

Alluvium 2: 1.1–9.8 4.5–12.5 Sand, medium to coarse grained, grey, very loose.

Alluvium 3: 2.3–10.8 3.7–5.5 Clayey sand to sandy clay, medium to coarse grained, grey, loose to medium dense.

Alluvium 4: 7.0–13.5 6.0–12.0 Gravelly sand/clayey Gravel, medium to coarse grained/medium plasticity, grey, medium dense/hard.

Residual Soil:

0.5–19.0 1.5–11.1 Silty clay to sandy clay, medium plasticity, grey brown mottled, firm to very stiff or hard.

Sandstone/ Siltstone:

2.0–21.8 - Sandstone/siltstone. Dark brown to grey, slightly to highly weathered.



Free groundwater was encountered during drilling at between one metre and 4.8 metres below the ground surface. Seepage was generally noted in the test pits at 0.65–2.4 metres depth. Groundwater depths in this area were observed to be 0.8–2.8 metres below ground level over a relatively dry four month period between April and August 2002. The water level at each location fluctuated between 0.1 metres and 0.3 metres at each location over this period.

Very soft, organic, silty clay extending to a depth of about 4.7 metres was encountered adjacent to the Myall River. The lateral extent of this very soft soil was not confirmed but is expected to be restricted to the river banks. The extent of soft soil under the proposed embankments would be confirmed before the final design stage.

Surface water was present in local areas creating difficult access conditions for site investigation. The soils at these locations, which were not drilled, may be softer than those inferred and encountered elsewhere and may require further investigation at a later design stage.

4.1.4 Cut 2

Cut 2 is a box cut located immediately north of the Myall River with a maximum height of 24 metres.

Field investigations encountered residual soils overlying rock units of the Bulahdelah Formation. The inferred profile is summarised in Table 4.4.


Unit Depth (metres)

Thickness (metres)

Description

Topsoil 0.0 0.25 Sandy clay to silty sand, fine sand, low to medium plasticity clay, brown.

Colluvium (coarse)

varies varies Sandy gravel with cobbles and boulders in matrix of silty clay, loose to very dense. Encountered in TP118, TP124 and TP127.

Colluvium (fine)

varies varies Silty clay, low to medium plasticity, mottled grey and red with gravel, very stiff to hard Encountered in TP118, TP124, TP125 and TP127.

Residual 0.2–2.1 0.4–0.7 Silty clay, low plasticity, mottled grey brown, very stiff to hard. Encountered in TP125, TP126 and TP127.

Sandstone 0.6–1.7 - Extremely to moderately weathered. Encountered in TP125 and TP126.

Complete drilling water loss was reported in two boreholes, which generally coincided with discontinuities such as joints.



Ground deformations related to the formation of the Myall Syncline structure and associated faulting has produced variably dipping joints and localised shear zones. The field mapping carried out in the area indicates that the dominant joint sets strike approximately north–south and west–east. This section of the route is aligned approximately north–south. Joint sets dipping west–east at about 45–65 degrees and at 70–90 degrees are therefore of significance to the batter design. Clay infill was noted along joint planes in the boreholes in the extremely weathered zone and need to be considered when assessing batter angles.

4.1.5 Cut 3

This short box cut adjoins Cut 2 and has a maximum height of about 5 metres.

Field investigations encountered residual soils overlying rock units of the Bulahdelah Formation. The inferred profile is summarised in Table 4.5. Groundwater was not encountered during the subsurface investigation carried out in this area.


Unit Depth (metres)

Thickness (metres)

Description

Topsoil 0 0–0.6 Silty sand/sandy silt, dark brown.

Alluvium: 0–1.0 4.1–4.3 Sandy clay, medium to high plasticity, dark brown to grey brown, soft to very stiff interbedded with clayey sand and gravelly sand. Encountered in TP 136, BH121 and BH122.

Colluvium: (Fine)

varies varies Silty clay, medium plasticity, brown, very stiff to hard. Encountered in TP132, TP133 and TP134.

Colluvium (Coarse):

varies varies Clayey gravel, medium to coarse grained, angular, grey, very dense. Encountered in TP133.

Residual Soil 1.4–5.1 0.1–1.2 Sandy clay, low to medium plasticity, grey, very stiff. Encountered in TP132, TP134, BH121 and BH122.

Sandstone 2.5 –- Extremely to highly weathered from 5 metres to about 10 metres in BH121 and moderately to highly weathered from 5.7 metres to at least 13.5 metres in BH122.

4.1.6 Cut 4

This cut adjoins Cut 3 and would be excavated through Colluvium considered to be the remnants of a previous ancient landslide. The inferred boundary of the landslide which is located within the colluvium in the vicinity of Cut 4 is illustrated in Figure 4.1. The proposed maximum depth of cut is about 13 metres.

Field investigations encountered significant depths of colluvium overlying soil and rock units of the Bulahdelah Formation. The inferred profile is summarised in Table 4.6.




Unit Depth (metres)

Thickness (metres)

Description

Topsoil 0 0–0.2 Sandy silt/clayey silt, low plasticity, dark brown.

Colluvium 0–0.2 0–25.4 Typically two types: (1) a fine colluvium of silty clay with some sand and gravel, very stiff to hard; and (2) a coarse colluvium comprising a poorly sorted mixture of high strength rhyolite gravels, cobbles and boulders in a matrix of very soft to hard, medium to high plasticity clay.

Residual 0–25.4 0–12.0 Silty clay, high plasticity, very stiff to hard. Bulahdelah Formation

>≈ 2.4 –- Siltstone, extremely and highly weathered, extremely low strength. Sandstone, extremely and highly weathered, very low to low strength.



Residual soil and extremely to highly weathered siltstone and sandstone of the Bulahdelah Formation was encountered beneath the inferred base of the colluvium.

Monitoring records from piezometers installed across the colluvium area, indicated that, up to February 2003, five piezometers were ‘dry’ and of the other five, only two showed groundwater levels about 4.3 metres and 6.4 metres respectively above the inferred colluvium base. Readings taken the day after the region had heavy rainfall for about two days measured no obvious response.

The RTA is monitoring inclinometers installed in the colluvium with no significant movement detected to date.

4.1.7 Fill 3

The maximum embankment height proposed along this section is 11 metres at Station 97700. The profile is broadly summarised in Table 4.7. Groundwater was not observed in the test pits along this section.


Unit Depth (metres)

Thickness (metres)

Description

Topsoil Nil 0.25 Sandy clay to silty sand, fine sand, low to medium plasticity clay, brown.

Colluvium (coarse)

Varies Varies Sandy gravel with cobbles and boulders in matrix of silty clay, loose to very dense.

Colluvium (fine)

Varies Varies Silty clay, low to medium plasticity, mottled grey and red with gravel, very stiff to hard.

Residual 0.2–2.1 0.4–0.7 Silty clay, low plasticity, mottled grey brown, very stiff to hard.

Sandstone 0.6–1.7 –- Extremely to moderately weathered.

4.1.8 Cut 5

This cut is at the northern interchange and is in two sections. The first cut is on the eastern side of the proposed Upgrade to the south of the interchange. The second cut is on the western side of the proposed Upgrade and to the north of the interchange. The maximum height of both cuts is 17 metres.

Field investigations encountered shallow colluvium (less than 2 metres) overlying residual soils and rock units of the Bulahdelah Formation, Burdekins Gap Basalt Member, Sams Road Rhyolite Member and the Muirs Creek Conglomerate. The inferred profile for each section of the cut is summarised in Table 4.8.




Unit Depth (metres)

Thickness (metres)

Description

Topsoil 0 0.2–0.3 Sandy silt/clayey silt, low plasticity, dark brown.

Colluvium 0–3.3 0–3.3 Typically two types: a fine colluvium of silty clay with some sand and gravel, very stiff to hard; and a coarse colluvium comprising of a poorly sorted mixture of high strength rhyolite gravels, cobles and boulders in a matrix of very soft to hard, medium to high plasticity clay.

Residual 0–9.0 0–8.8 Silty sand with some gravel and medium plasticity silty sandy clays. Stiff to very stiff grading to hard. The sand soil was assessed to be of loose consistency.

Rock Formation >≈ 6.7 –- Weathered rhyolite, olivine gabbro and sandstone. Extremely weathered to moderately weathered. Up to high strength.

4.1.9 Fill 4

This fill is located on slopes formed by colluvium to the south and alluvium to the north overlying sedimentary rock formations. The maximum proposed embankment height along this section is 6.5 metres at Station 99200. The profile is broadly summarised in Table 4.9. Groundwater was encountered between 0.3–1.2 metres below the surface during the investigation.


Unit Depth (metres)

Thickness(metres)

Description

Topsoil 0 0–0.55 Silty sand/sandy silt, dark brown.

Alluvium: 0–1.0 4.1–4.3 Sandy clay, medium to high plasticity, dark brown to grey brown, soft to very stiff interbedded with clayey sand and gravelly sand.

Colluvium: (Fine)

Varies Varies Silty clay, medium plasticity, brown, very stiff to hard.

Colluvium (Coarse):

Varies Varies Clayey gravel, medium to coarse grained, angular, grey, very dense.

Residual Soil 1.4–5.1 0.1–1.2 Sandy clay, low to medium plasticity, grey, very stiff.

Sandstone 2.5 –- Extremely to highly weathered from at 5–10 metres.



4.2 Cut Batter Design

4.2.1 General

This section discusses batter design for Cuts 1, 2, 3 and 5. Section 4.2.3 discusses specific slope design for Cut 4 through the colluvium between Station 96750 and Station 96980.

The objective of the adopted profiles was to achieve batter slopes that:

provide a design with low risk of instability or disruption to highway operations by rockfalls in accordance with the Australian Geomechanics Society guidelines (Vol. 37 No 2 May 2002);

satisfy the requirements of the RTA Road Design Guide; and

minimise the need for external support, except where economically justified.

The cuttings in both the adjacent Bulahdelah to Coolongolook Freeway and the existing local Pacific Highway in similar materials demonstrate the potential impact of adversely oriented joints in the rock mass and the influence of deep weathering profiles on the cutting design.

Inspection of cuttings during construction by a suitably experienced geotechnical engineer or engineering geologist is recommended to:

identify any adversely oriented defects;

confirm design assumptions on rock quality particularly where fault zones are encountered; and

advise on appropriate support measures should defects or rock quality be adverse.

4.2.2 Classification of materials

The materials expected to be encountered on site have been divided into five classes based on substance strength and fracture spacing. These characteristics are considered to be the primary control of rock slope stability and the adopted design slope is given for each class.

The five types together with the adopted design slopes are shown in Table 4.10.



Table 4.10: Material Classification

Material Strength Material Class Description

UCS (MPa)

Point Load (Is 50 – MPa)

Block Size (millimetres)

Slope Design Horizontal to Vertical

Soil –- -– -– R5

Extremely Low

<1 <0.03 –-

2:1

Very Low 1–3 0.03–0.1 >300 R4

Low 3–10 0.1–0.3 <300

1.5:1

Low 3–10 0.1–0.3 >300 R3

Medium 10–30 0.3–1 <300

1:1

Medium 10–70 1–3 >300 R2

High >70 >3 <300

0.5:1

R1 High, Very high to Extremely High

>70 >3 >300 0.25:1

Note where both strength and fracture block size is not satisfied together, the material class reduces by one. By primarily using the above material classifications, slope designs can be assessed from borehole logs and confirmed on site during construction.

4.2.3 Batter Profiles

Batter profiles were assigned to the five material classifications as indicated in the following Table 4.11 and summarised in Figure 4.2.

Table 4.11: Batter Profile Schedule

Maximum Slope Batter (H:V) Cut Profile Type Unreinforced Reinforced

Geological Profile (Material Classification)

Notes

A 2:1 0.5:1 Soil mantle, colluvium, residual soil, extremely weathered rock, extremely low to low strength (R5).

Consider soil nailing, draining slope etc

B 1.5:1 0.5:1 Highly weathered or moderately weathered and fractured rock, very low to low strength (R4).

Deep Weathering Profile


Bulahdelah – Upgrading the Pacific Highway Technical Paper 11 Table 4.11 continued

Maximum Slope Batter (H:V) Cut Profile Type Unreinforced Reinforced

Geological Profile (Material Classification)

Notes

C 2:1 0.5:1 Soil Mantle (R5).

1.5:1 0.5:1 Highly weathered or moderately weathered and Fractured Rock (R4).

1:1 0.5:1 Moderately weathered to slightly weathered, low to medium strength rock (R3).

0.5:1 0.5:1 Slightly Weathered to Fresh, Very High Strength Rock (R1 or R2).

D 2:1 0.5:1 Soil mantle (R5). Shallow weathering profile

0.5:1 0.5:1 Slightly Weathered to Fresh, Very High to extremely high strength Rock (R1 or R2).

The recommended batter profiles are based on the following assumptions:

all cuts less than or equal to 3 metres high will be excavated at 2H:1V irrespective of material type;

berms will be located immediately below residual soil (the residual soil is typically 2–5 metres deep);

a maximum batter height between intermediate benches of 7 metres (as specified by the RTA);

minimum bench width of 4 metres (for maintenance and containing material fall) or 3 metres with catch fence;

recommended cut profiles are for individual batters between benches;

the provision of a catch pit at the base of the lowest batter for rock slopes steeper than 1.5H:1V. Depending on how close the batter is to the road, this requirement may be mitigated by scaling, localised mesh and shotcrete or rockbolts; and

a “V”- drain is provided at the toe of the lower batter slope if no catch pit is provided.


Notes:

1. Landscaped protection for batters flatter than 1.5:1 and localisedbatter stabilisation for steeper batters, as required.

2. 2:1 (H:V) batters to be vegetated to minimise erosion.

3. Cut batter slopes to be rounded-off at ends of cut to merge withnatural surface.

4. Drainage detail not shown.

5. Consideration could be given to increasing the bench heightinterval to 10 metres subject to detailed geotechnical investigationand favourable conditions.

Figure 4.2 Recommended Batter Profiles

CUT PROFILE SCHEDULE

Cut ProfileType

Soil mantle, colluvium, residual soil,extremely weathered rock, extremelylow to low strength (R5)

Highly weathered or moderatelyweathered and fractured rock, very lowto low strength (R4)

Soil mantle (R5)

Highly weathered to slightly weathered,low to medium strength rock (R3)

Moderately weathered to slightlyweathered, low to medium strengthrock (R3)

Slightly weathered to fresh, very highstrength rock (R1 to R2) – see Note 5)

Soil mantle (R5)

Slightly weathered to fresh, very highto extremely high strength rock(R1 to R2)

A

B

C

D

2:1

1.5:1

2:1

1.5:1

1:1

0.5:1

2:1

0.5:1

Maximum SlopeBatter

(Horizontal:Vertical)

UnsupportedGeological Notes

Not to scale

Boundaryfence

Catch drain(typical)

Soil profiles batteredat 2H:1V, height variablefrom 2 metres to 5 metres

7 metres intervalsbetween benches

2:1

Cut Profile Type(refer text)

1.5:1 2:1

2:1

2:11.5:12:1

4 metres wide berms(typical)

1.5:1

3 metres verge widthat toe of 0.5H:1V cut.Otherwise, 1.7 metresverge width

Fill batter1.5H:1V to 2H:1V

A BC

D


Recommended batter profiles for each cut are presented in Table 4.12.

Table 4.12: Recommended Batter Profiles

Station (metres) Cut

From To

Max Cut Depth (metres)(1)

Geological Notes Recommended Batter Profile(2)

f1 92600 93050 4 Residual soil overlying shallow siltstone and sandstone.

A

2 95880 96020 7 Residual soil overlying shallow siltstone and sandstone.

B

96020 96500 24 Residual soil overlying shallow siltstone and sandstone. .

C

96500 96600 13 Residual soil overlying shallow siltstone and sandstone.

B

3 96600 96750 5 Residual soil overlying shallow siltstone and sandstone.

B

4

(Colluvium)

96750 96980 13 Deep colluvial soils overlying extremely weathered siltstone.

A

5 East 98050 98550 17 Residual soil overlying steeply west dipping sequence of sheared rhyolite and olivine basalt.

B/C3

5 West 98550 98860 16.5 Residual soil overlying steeply west dipping sequence of olivine basalt and conglomerate.

B/C3

1. Maximum cut depth on alignment centreline.

2. Refer earthworks cut profiles.

3. Subject to detailed design.



The regional geology and the field mapping performed along the preferred route indicate defects in the sandstone/siltstone and volcanic rock mass north of the Myall River. They comprise steeply dipping bedding (60–85 degrees) and steep to near-vertical joints and shear zones. The shear strength along these defects may be less than the overall parameters assumed for the rock mass due to clay infill or previous shear movement. Where bedding/joint defects occur in unfavourable orientations, flatter batter slopes would be required to avoid undercutting these defects and to provide additional slope reinforcement.

Conversely where the quantity of bedding/joint defects is minimal or at a favourable orientation, steeper batter slopes may be considered subject to regular inspections by a geotechnical engineer. Consideration could also be given to increasing the bench height interval to 10 metres and reducing the bench width from 4 metres to 3 metres in cuts where the quality of the exposed rock is such that the perceived maintenance requirements would be minimal over the long term. The benefits arising from steeper batters, increased bench intervals and smaller bench widths include less material to be excavated and a reduced road corridor width. The geometry of potential batters assuming favourable conditions is illustrated in Figure 4.3.



4.3 Colluvium Area Cut 4

The colluvium area is inferred to result from previous landslide activity which has deposited rhyolite boulders from the Bulahdelah (Alum) Mountain in a matrix of clay (possibly a residual of the Burdekins Gap Basalt) over the sedimentary rock of the Bulahdelah Formation. Hummocky ground surfaces and slickensided joints near the base of colluvium indicate that large scale ground movement has occurred but probably not within the past, say thousand years.

The colluvium area is situated near the toe of Bulahdelah (Alum) Mountain. The centre line of the proposed roadway through the colluvium is located about 150–200 metres to the east of the nearest residence. Ground slopes within the footprint of the proposed cutting range from approximately 7 degrees to 12 degrees down to the west. Downhill of the proposed cutting the ground slopes reduce to about 5 degrees. Approximately 400 metres uphill and to the east of the proposed cutting, ground slopes increase to approximately 20 degrees and 30 degrees gradually rising to sub-vertical cliffs some 500 metres to the east of the proposed cutting.

Some boulder sized material (typically 0.5–5 metres in size) was previously released from the cliff faces and rolled down the hill. Scattered boulders located over the natural slope near the toe of the cliffs extending to the footprint of the proposed cutting, though the majority are located within approximately 50 metres of the toe of the cliff. A typical boulder on the slope is shown in Figure 4.4.

The proposed cutting is underlain by colluvium extending to depths of about 25 metres below existing ground surface at the borehole locations. The colluvium generally overlies the Bulahdelah Formation comprising fine grained sandstones and siltstones, although some areas may contain colluvium overlying residual clays then bedrock. Colluvium was encountered to 18.45 metres and residual clays to greater than 30 metres at BH117 as shown in (refer Figure 2.3).

Uphill of, and within the majority of, the footprint of the proposed cutting, the ground is covered in dense vegetation with small sized shrubs and tall mature trees. An existing unsealed access road runs through the footprint of the proposed cutting following overhead power lines. The vegetation in the gullies on the flanks of this area is greener than other locations, indicating the possible presence of surface water.

A total of 10 piezometers were installed in the Colluvium area in the vicinity of Cut 4 to monitor long term groundwater fluctuations. The piezometers were installed at different stages of the investigation between May 2002 and December 2002. These have been monitored at regular intervals. Groundwater monitoring carried out between May 2002 and February 2003 indicates that piezometers in BH130, BH131 and BH132 were dry, which indicates that the groundwater table lies below the piezometer tip level. Water level readings taken from the other seven boreholes fluctuated from being dry to a water level just a few metres above the colluvial base following rainfall events.



Piezometers in boreholes BH116, BH123, BH127, BH130 and BH131 were monitored by using data logger units between March 2003 and August 2003. The readings indicate that piezometers BH116 and BH130 remained dry during the monitoring period. The water level in BH131 was found to lie 11.7–12.2 metres below ground level during this period. Water level monitoring results from piezometers BH123 and BH127 fluctuated in response to rainfall events. Both piezometers showed a similar water level variation pattern with time due to rainfall events.

The highest recorded water level between May 2002 and February 2003 for both BH123 and BH127 was 9.4 metres and 6.4 metres respectively below ground level. The groundwater levels in these two boreholes peaked at about 8 metres and 2 metres respectively during March 2003 and August 2003 following a storm event and then showed a decline to depths of about 9 metres and 4 metres respectively.

The above discussion applies to conditions encountered up to August 2003 following a period of comparatively low rainfall. Groundwater levels are expected to increase during periods of high rainfall, unless control measures are adopted.

Two inclinometers were installed to monitor ground movements. At this stage limited monitoring results indicate that no movement outside the detection limits of the monitoring equipment has occurred.

4.3.1 Landslide Risk Assessment

The report on Colluvium Area (Cut 4) Stability (Parsons Brinckerhoff 2004a) considered that the proposed cutting through the colluvium presented the following potential hazards for the proposed Upgrade and adjacent houses:

Hazard A: Boulder falls from the cliff face or natural hillside slope above Cut 4;

Hazard B: Gravels, cobbles or boulders released from and rolling down the cut face;

Hazard C: Small scale ‘shallow slump’ failure of the cut face;

Hazard D: Large scale overall slope failure by slippage along the colluvial/ bedrock or natural soil interface and daylighting near the toe of Cut 4; and

Hazard E: Large scale overall slope failure encompassing the entire road. The failure surface is the same as Hazard D, but runs beneath the roadway and daylights downslope of Cut 4.

These hazards are illustrated on Figure 4.5.



The likelihood of failure occurring and its potential impact was assessed for each hazard. Likelihood is defined as the product of the probability that the failure will occur and, once it has occurred that it will travel as far as the element at risk. The elements at risk were identified as either vehicles travelling through Cut 4 or the houses located downslope of Cut 4. A summary of the each hazard assessment for each hazard is described below and presented in Figure 4.6.



The risk assessment was carried out in accordance with the Guide to Slope Risk Assessment (Stewart 2002), and the Landslide Risk Management Concepts and Guidelines (Australian Geomechanics Society 2002). Potential Risks have been compared to existing risks to people living in NSW. Further details are provided in the Report on Colluvium Area (Cut 4) Stability (Parsons Brinckerhoff 2004a).

Existing Risks to People in New South Wales

In NSW, risks associated with many everyday circumstances have been documented. For instance, each year people in NSW face 110 chances in a million of dying due to an accident at home, 60 chances in a million of dying dye to an accidental fall 35 chances in a million of dying as a pedestrian struck by a motor vehicle and 18 chances in a million of dying due to accidental poisoning (PlanningNSW 2002). Table 4.13 summarises these risks.



Table 4.13: Risks to Individuals in New South Wales

Risks Averaged Over the Whole Population Chances of Fatality per Person per Year

Cancers from all causes 1,800 chances in a million

Accidents at home 110 chances in a million

Accidental falls 60 chances in a million

Risk criteria for industrial land uses1 50 chances in a million

Pedestrians struck by motor vehicles 35 chances in a million

Homicide 20 chances in a million

Accidental poisoning 18 chances in a million

Fires and accidental burns 10 chances in a million

Risk criterion for commercial land uses1 5 chances in a million

Electrocution (non-industrial) 3 chances in a million

Falling objects 3 chances in a million

Therapeutic use of drugs 2 chances in a million

Risk criterion for residential land use1 1 chance in a million

Risk criterion for hospitals, schools, etc1 0.5 chances in a million

Cataclysmic storms and storm floods 0.2 chances in a million

Lightning strikes 0.1 chances in a million

Meteorite strikes 0.001 chances in a million Source: PlanningNSW 2002 1. The risk criterion relates to the risk generated from a particular hazardous facility or activity, It represents an additional

level of risk above risks that already exist.

By taking into account these and many other known and tolerated risks, the Department of Infrastructure, Planning and Natural Resources (formerly Planning NSW) has suggested that people in residential areas should not be exposed to more than a one in a million chance of a fatality each year due to accidents at hazardous industrial facilities. More sensitive areas, such as hospitals and schools, should not be exposed to a chance greater than 0.5 in a million of fatality each year dues to accidents at nearby hazardous industrial facilities. These risks from particular facilities or activities are additional to risks that already exist.



Hazard A

The risk to the proposed road alignment has been assessed for:

existing boulders sited in the vicinity of the proposed road alignment; and

rock fall from the cliff face above the road.

Field observations identified a large number of boulders within 50 metres of the toe of the cliff faces. However, some scattered boulders were located on the proposed road alignment.

Based on these observations and the results of a risk analysis of falling rocks on steep slopes using the RocFall computer program, it was considered that the existing boulders observed near the proposed road alignment did not reach their present position by rolling from the base of the cliff but were part of an ancient landslide and were carried by the landslide (or colluvial) mass.

Rock falls have obviously occurred from the cliff in the past based on the presence of large numbers of boulders near its toe. Therefore, although further rock falls could occur, the risk to life for persons most at risk — either in vehicles on the road or residents downhill of the road — is assessed as 1 in 2 million. This risk is considered ‘not credible’ as defined by the Landslide Risk Management Concepts and Guidelines (Australian Geomechanics Society 2002).

To reduce the risk of existing boulders rolling into the cutting, all boulders within a horizontal distance from the proposed crest equal to twice the depth of the cutting would, be inspected by an engineering geologist/geotechnical engineer before or during excavation. Any boulders considered at risk of rolling into the cutting, either during or after construction, would either be removed or appropriately shored or anchored to the slope.

Hazard B

Gravel to boulder sized blocks in a clayey, silty or sandy matrix are expected to be exposed on the cut faces. Some of these blocks have the potential to become dislodged from the cut face with weathering and erosion of the supporting matrix occurs. Alternatively these blocks may be in a loose state following excavation and final trimming of the batter.

RocFall modelling indicates that approximately 0.8 percent of modelled rocks would reach the carriageway, assuming a maximum cut face height of 7 metres, batter angle of two horizontal in one vertical (27 degrees) and a shoulder width of 2 metres.

However, the design shoulder width would be 2.5 metres with an additional 1.7 metre verge width. Therefore, although the likelihood of blocks detaching from the face may be 1 in 100, the likelihood of their hitting the element at risk (vehicles) is considered to be 1 in 700,000 for vehicles and 1 in 20 million for houses downhill.



To further reduce the potential risk to vehicles and road users, it is recommended that care is taken during construction with final trimming of cut batters to remove all loose gravels, cobbles and boulders exposed on the face. Suggested management techniques may involve regular inspections on an annual basis for the first five years to assess the extent of weathering and erosion of the face, and the need for additional removal of loose material. The need for further monitoring should be determined based on the outcome of this monitoring program. These risk reduction strategies should reduce the risk of Hazard B to the limit of ‘acceptability’ or a ‘not credible’ risk (Australian Geomechanics Society 2002).

Hazard C

Based on a design slope of 2 horizontal:1 vertical, and the nature of material anticipated on the cut slopes, the likelihood of small scale shallow slump failure on the cut face occurring is 1 in 10,000. This is considered ‘unlikely‘ based on Australian Geomechanics Society(2000) criteria. The proposed slope geometry is comprised of maximum 7 metre high cut faces at 2 horizontal:1 vertical with a total shoulder and verge width at road level of approximately 4.2 metres. Therefore, for the proposed cut slope geometry an angle of shearing resistance of approximately 20 degrees for the slide material is required to maintain the slide debris outside of the carriageway. Laboratory shear strength testing of the matrix materials recovered from the colluvial mass, has indicated values of 25 to 40 degrees. These values will probably be higher based on the presence of gravels, cobbles and boulders within the colluvium.

The assessed risk to life for persons most at risk is 1 in 1.3 million for road users and 1 in 13 million for the occupants of the houses downhill. No treatment plans to reduce the existing risk are considered necessary at this stage. However, ongoing monitoring would be undertaken on an annual basis for the first five years to assess the extent of weathering and erosion of the face, and to recommend additional removal of loose material if required. The need for further monitoring should be determined based on the outcome of this monitoring program.

Hazards D and E

The likelihood of failures identified as Hazards D and E occurring would be mainly dependent on piezometric levels within the colluvial mass and the effect of rainfall events on these levels. Piezometers were installed through the colluvium in the vicinity of the proposed Cut 4 to monitor groundwater levels.

Given the existing groundwater information and the results of the stability analyses, it is considered that the likelihood of failure, identified as Hazards D and E, occurring is 1 in 100,000. This is considered to be ‘rare’ (Australian Geomechanics Society 2002).

The overall likelihood of Hazards D and E occurring and hitting a vehicle on the proposed Upgrade is 1 in 1 million (‘rare’) and hitting houses downhill of the proposed road is also 1 in 1 million (‘rare‘).



The assessed risk to life for persons most at risk is 1 in 20 million for road users and 1 in 2.5 million for residents of the houses downhill. This is considered to be a ‘not credible’ risk (Australian Geomechanics Society 2002).

However, the groundwater response in the colluvial mass to rainfall events is critical to the assessment of likelihood of failure for Hazards D and E. Groundwater monitoring has not been completed over a sufficient period of time to correlate piezometric level variations to rainfall events. An assessment of the rainfall intensity recurrence intervals required to reduce Factors of Safety to unacceptable levels should therefore be undertaken to establish a relationship between rainfall and piezometric conditions.

Following additional monitoring and by consideration of historic rainfall data, a more detailed assessment on the likelihood of failure can be completed. Rainfall events and piezometric conditions should be monitored for at least the first 5 years after construction and this risk assessment reviewed on a bi-annual basis to confirm that the assumptions made in this report are appropriate.

Risks may also be present to life and equipment during the construction of these batters. As this is dependant on a number of factors that are not known (eg. construction techniques) they cannot be assessed yet.

4.3.2 Colluvium Batter Stability Analysis

The slope stability program ‘SLOPE/W’ version 4 was used to model the geotechnical information and calculate the stability of a range of cut slope profiles. Two sets of soil parameters were chosen, one for each of the fine and coarse colluvium. The soil parameters used for the model were based on experience with similar soils, laboratory testing and from published correlations between plasticity index and angle of shearing resistance and between the angle of shearing resistance and effective stress cohesion. The tension crack allows for the possibility of ground movement prior to initiation of instability.

The cut profile analysed corresponded to:

the deepest proposed cut in the colluvium zone of 14 metres (it is noted that the concept design described in Technical Paper 4 — The Proposal proposes a maximum depth of 13 metres, thereby presenting a slightly reduced stability risk);

a preferred bench width of 4 metres;

a 7 metre maximum vertical height between benches; and

a nominal 2 metres deep tension crack at the top of the colluvium.



Results of Stability Analysis in Colluvium

Table 4.14 below summarises the results of analyses that consider high and low groundwater levels for different slope geometry cases. The sensitivity of the results to the adopted soil parameters is investigated using upper and lower bound values. Table 4.15 considers the impact of seismic loading on the models analysed in Table 4.14.

Table 4.14: Calculated Factors of Safety in Colluvium

Factor of Safety Geometry Profile Description Adopted Shear Strength Parameters1

Target FoS

ru = 0.25 ru = 0

A 2H:1V Lower2

Upper3)

>1.2-1.3

>1.5

1.0

1.4

1.4

1.8

B 1H:1V Lower2

Upper3

>1.2–1.3

>1.5

0.7

1.0

1.0

1.4

C Lower slope 1H:1V

Upper slope 2H:1V

Lower2

Upper3

>1.2–1.3

>1.5

1.0

1.3

1.3

1.8

D Lower slope 0.5H:1V

Upper slope 2H:1V

Lower2

Upper3

>1.2–1.3

>1.5

0.9

1.3

1.3

1.7

1. Proposed in concept design. Refer Technical Paper 4 — The Proposal. 2. Lower bound parameters c’ = 5 kPa, φ = 25o,γ’ 19 kN/m3. 3. Upper bound parameters c’ = 10 kPa, φ’ = 30o, γ’ = 19 kN/m3. 4. Bold indicates result does not comply with design criteria.

Table 4.15: Calculated Factors of Safety in Colluvium under Seismic Loading

Factor of Safety Geometry Profile Description Adopted Shear Strength Parameters1

Target Factory of Safety ru = 0.25 ru = 0

A 2H:1V Lower2

Upper3

>1.1

>1.1

0.8

1.0

1.0

1.4

B 1H:1V Lower2

Upper3

>1.1

>1.1

0.6

0.8

0.8

1.1

C Lower slope 1H:1V

Upper slope 2H:1V

Lower2

Upper3

>1.1

>1.1

0.7

1.0

1.0

1.3

D Lower slope 0.5H:1V

Upper slopes 2H:1V

Lower2

Upper3

>1.1

>1.1

0.7

1.0

1.0

1.3

1. Proposed in concept design. Refer Technical Paper 4 — The Proposal. 2. Lower bound parameters c’ = 5 kPa, φ = 25o,γ’ 19 kN/m3 3. Upper bound parameters c’ = 10 kPa, φ’ = 30o, γ’ = 19 kN/m3 4. Bold indicates result does not comply with design criteria.



It is apparent that with the parameters used in the analyses, the calculated overall factor of safety against a deep circular slip within the colluvium is acceptable for the 2 horizontal:1 vertical batter slopes providing there are low groundwater levels. Should high groundwater levels exist, the lower bound model indicates the slope has marginal stability and would not meet the target factor of safety unless suitable stabilisation measures were taken.

If a steeper overall batter is favoured in order to reduce the volume of cut material and land take, then soil stabilisation measures would be necessary. A profile incorporating a reinforced lower slope with a shallower batter slope above (Geometry C and Geometry D, see Table 4.13 above) appears to provide possible alternatives.

The lower bench slope could be formed at a batter of between 0.5 horizontal:1 vertical and 1 horizontal:1 vertical which would require reinforcement with soil nails and a facing of shotcrete or prefabricated panels.

Geometry B which contains upper and lower batter slopes of 1 horizontal:1 vertical failed to meet factor of safety targets for both high and low groundwater levels.

All batter options require drainage measures to reduce the groundwater level and to reduce infiltration into the soil. A buffer zone at the toe of the slope may be required depending on the slope angle and whether the face is covered or exposed. For slopes less than or equal to 2 horizontal:1 vertical, a ‘V’-ditch drainage channel would be sufficient to function as a buffer zone. For exposed steeper batter slopes a catch pit may be required at the toe to retain any rock fragments that might fall.

The target factor of safety adopted for models incorporating seismic loading is lower than under normal conditions to reflect the low likelihood of this event occurring. A target of 1.1 or greater is considered acceptable. The analyses indicate that under seismic loading and with high groundwater levels (that is, ru approaches about 0.25) the stability is compromised. With low water levels (that is, ru approaches zero) the stability is marginal if lower bound soil parameters are used. With upper bound soil parameters the factor of safety exceeds the target for all cases analysed.

The assessed low factor of safety under earthquake loading should be considered in the context of the conservative strength parameters; the assumption of a high piezometric level, together with high earthquake acceleration (a = 0.12g) occurring all at the same time. The risk level associated with all three of these conditions occurring at the same time is considered to be ‘very low’ or less based on the Australian Geomechanics Society guidelines (2002) and is discussed further in the Report on Colluvium Area Stability (Parson Brinckerhoff 2004a).

Geometry A has been adopted for the concept design with a maximum cut depth of 13 metres. Therefore the analysed cut depth of 14 metres has an additional degree of conservatism.



The stability analysis results confirm that Geometry A (refer Tables 4.14 and 4.15)should be adopted, groundwater has a significant influence on stability and demonstrates the need to provide adequate drainage management controls and slope maintenance procedures, and a treatment plan to maintain or reduce risks. Regular monitoring of groundwater levels and ground movement up to, during and after construction is proposed.

The following would be required to ensure that batter stability is maintained within acceptable risk criteria:

before, or during, excavation additional inspection of boulders immediately upslope of the cutting would be carried out. Where boulders remain protruding from the cut face it would be necessary to assess their long-term stability. Small boulders would be removed and the cut face restored with compacted or stabilised fill. Large boulders should be drilled to assess the proportion of boulder inside the slope to evaluate their stability. Treatment would involve total or partial removal, or stabilisation with rock anchors;

during construction and final trimming of batter faces, care should be taken not to loosen boulders in the face. Regular, on going inspection of the cut face would be undertaken during construction and operation;

ongoing monitoring for ground movement would be undertaken and continued following completion of the Upgrade. It would be prudent to install remote groundwater monitoring systems and establish trigger levels to prompt precautionary action should groundwater levels approach those assumed in the design; and

risk assessment should be reviewed on a bi-annual basis to include the results of the ongoing monitoring.

4.4 Batter Protection

The proposed batter slopes vary according to the materials in which the cut slopes will be excavated, as shown in Table 4.11. The materials range from residual soils to high strength sandstone. Slopes excavated in soil and highly weathered rock (Batter profiles A, B and the upper sections of C and D) should be protected from long-term degradation caused by exposure to the elements. Revegetation with shrubs would be carried out as soon as possible after exposure as possible. It is anticipated that batters excavated in moderately or less weathered rock 1 horizontal:1 vertical and steeper will not require protection.

In general, stabilisation of rock batters by routine rock bolting, dowels or shotcrete is not expected to be required, although localised treatment may be necessary. Bedding and jointing in the sedimentary rock and defects in the volcanics are reported to be steep and should not intercept in the steeper cuts.



During excavation loose rock would be scaled from batters and the batters inspected for adversely orientated joints, large defects or sheared zones that may influence their stability. Batter protection measures would also incorporate lightly spread topsoil which could be spread with a bulldozer and chain.

Boulders will be encountered during excavation through colluvium and some are anticipated at the batter face. The proportion of exposed boulder to that embedded should be assessed to determine appropriate treatment. Boulders can be left in place, removed and the slope reinstated, or partially removed by blasting or rock breaker. Drilling through the boulders with an air track drill to assess the size of the boulder has been successfully undertaken on other projects.

4.5 Excavated Materials from Site

4.5.1 Characteristics of Excavated Materials

Approximately 200,000 cubic metres of general earthworks material would be imported from the project immediately to the south for the construction of embankments. All other general fill for the embankment construction would be derived from the proposed road cuttings on site. The characteristics of the imported material are not available and therefore have not been quantified.

The materials excavated from cuttings on site would comprise residual soils, colluvium (sandy gravel in silty clay matrix), highly weathered to fresh sandstone, siltstone and volcanic rock. All material is considered suitable for general fill, although oversize boulders of strong rock in the colluvium will need to be screened then broken down to a size not greater than two-thirds the proposed fill placement layer thickness. Mixing may also be necessary to avoid pockets of contrasting materials.

Excavation for Cut 2 is expected to involve blasting of fresh, high strength sandstone with various degrees of difficulty in ripping the more weathered sandstone and siltstone. About 150,000 to 200,000 cubic metres of rock may require blasting. Accurate quantities cannot be assessed as other factors such as production rates, and quality and quantity of equipment, will affect the amount of material requiring blasting.

Blasting is expected for 150,000 to 200,000 cubic metres of rock. Slightly weathered and fresh durable rock should provide a good material for use as a bridging layer on soft ground or for general use throughout the embankments.



Based on the results of the investigation a preliminary California Bearing Ratio (CBR) in the order of 3 percent could be adopted for design of pavements on soil subgrade embankments. The benefit of lime or cement stabilisation of the clayey soil subgrade has not yet been tested, although materials selected from the cuts are envisaged to be able to be stabilised to achieve a California Bearing Ratio of greater than 10 percent. This layer would form a select fill to improve trafficability and provide support for the pavement. Crushed or processed rock excavated from the cuts is expected to have design California Bearing Ratio values in the order of 10–15 percent.

4.5.2 Unsuitable Material

Unsuitable material is defined as material that is not suitable for use as compacted fill. This may be due to a high proportion of an organic content, a high plasticity index or liquid limit, moisture content is outside the range specified, large material size relative to the layer thickness, or the soil contains acid sulphates or is contaminated.

Most of the samples recovered during the field investigations recorded laboratory field moisture content higher than the optimum moisture content (OMC). The standard RTA earthworks specification limits the maximum moisture content to 90 percent of optimum moisture content. It may be necessary to recommend a variation to this if it is found through further investigation that high moisture content soils predominate across the proposed alignment. Excavated soil with moisture contents too high or too low could be conditioned on site to achieve the specified range. The soils can also be excavated and left to dry as well as incorporated with drier ‘rocky’ material in pug mills.

Oversize material such as boulders within the colluvium or from excavation by blasting or ripping in the sandstone can be screened during excavation. This material could be used for purposes other than fill or be broken down by a rock breaker or crusher.

Acid sulphate soils could also be made suitable as fill material by the appropriate addition and mixing of lime under controlled conditions.

Top soil thicknesses along the alignment ranged from zero to 0.55 metres. An average of 0.2–0.4 metres should be allowed for stripping where necessary. Stripped topsoil should be either stockpiled separately for later use in landscaping or spoiled if re-use is not possible.

4.5.3 Commercial Sources of Construction Materials

The location of known commercial sources of construction materials, compiled from information supplied by the Department of Mineral Resources (1999), are shown in Figure 4.7. These data were compiled from information supplied by the Department of Mineral Resources. An engineering assessment of material quality and suitability for use in embankment and pavement construction should be undertaken during the detailed design phase as required.


Resource Sizes (tonnes) Commodity

10,000,000 –

1,000,000 –

100,000 –

10,000 –

0 –

Unknown

100,000,000

10,000,000

1,000,000

100,000

10,000

Coarse aggregate – armour stone

Coarse aggregate – hard rock

Coarse aggregate – shale

Conglomerate

Gravel – fluvial

Sand – construction

Unprocessed construction materials

Shire boundary

Roads

Rivers

50 kilometres radius around Bulahdelah

Site ID1550

0 30

kilometres

15 Figure 4.7 Operating Quarries and Prospective Quarry Sites

2177

1505

16959

9433

8951

1557

1524

1732

2445

2159

1731

2444

1458

21582244

1550

9131

WILLIAMTOWN

KARUAH HAWKS NEST

BULAHDELAH

FORSTER

7982

169961467

16716

16718

16830

14139

14181

16482

16481

16475

164771647616478

16483

16484

16697

14154

14171

9127

14562

7839

1647410374

1399

16520

1651916998

14561

2143

7949

14295

1506

16997

14314

10145

796

2136

1606

Booral Road

Pacific Highway

Pacif

ic Hi

ghw

ay

The LakesWay


Opportunities to utilise project related borrow sites to the south and widening or laying cuttings back to avoid the need to use commercial resources should be considered where possible to promote sustainable construction and balance earthworks on the project.

The engineering assessment would be consistent with RTA specifications for road construction materials and include laboratory testing of the following properties:

durability;

strength;

dispersion;

grading; and

reactivity.

4.6 Embankments

4.6.1 Settlement Assessment in Fills

Settlement along the fills can be critical where embankments are constructed on soft compressible soils and there is a risk that primary consolidation settlement would continue beyond the construction period. Combined with secondary (creep) consolidation of the soft soils and internal creep of the fill material itself, settlement has the potential to exceed design criteria, particularly between structures and adjoining embankments.

Critical settlement locations were identified at structures, at maximum fill embankment height and/or at soft soil foundations. In all locations except at the northern interchange, the maximum fill height and critical foundation soils occurred at a structure. At the northern interchange the maximum approach embankment heights are not located at the overpass bridges. Settlement is expected to be most critical at the Myall River Bridge where embankments are high and soft soil was encountered to depths of 4.7 metres at borehole locations.

The adopted performance criteria for evaluating settlements have been based on that adopted for recent Pacific Highway Upgrade Projects such as Yelgun to Chinderah, and Lane Cove Tunnel.

The performance criteria are:

residual surface settlement limited to a maximum of 100 millimetres over a 10 year maintenance period. Alternatively, 90 percent primary consolidation should occur before pavement construction;

maximum internal settlement (creep settlement within the fill) over any 12 month period following completion of construction completion of 15 millimetres;.



maximum internal settlement from date of construction completion of 50 millimetres; and.

differential settlement (change in grade) of 0.3 percent longitudinally and 0.1 percent transversely.

In order to meet the performance criteria, it is common practice to surcharge the fill. Where significant settlement occurs, the surcharge fill becomes part of the embankment and the surcharge fill used must conform and be placed and compacted to the requirements of the specification. Allowance must also be made for the volume of fill lost due to settlement, particularly in regard to the setting out of the embankment toes.

Where fill embankments are constructed over soft foundations, a nominal surcharge of 1 metre should be placed to cater for settlement and to preload the subgrade to minimise the impact of subsequent traffic loading. In no circumstances should there be a net increase in fill height when the pavement is constructed.

4.6.2 Settlement Analysis

Risk Issues

Estimation of the magnitude and rate of settlement is influenced by various factors including:

the thickness of compressible soil — the field and laboratory test data indicate that the soft and firm alluvial clays are likely to be the most compressible strata within the subsurface soil profile across the floodplain section of the proposed alignment. The magnitude of compression is dependent on the applied load and the thickness of the compressible layers;

the consolidation parameters of the clay — requires interpretation of in situ and laboratory test results and the selection of design parameter profiles for use in analysis and prediction. Some grouping of results into general areas and adoption of best-fit parameter profiles has been assumed to simplify the analysis. In particular, the analyses are sensitive to values of compression ratio adopted; and

previous stress history of the clay (Over Consolidation Ratio (OCR) profile) — requires the estimation of pre-consolidation stresses using in situ and laboratory test data. Previous experience has shown that assessment of the appropriate over consolidation ratio profile is prone to uncertainty and that the previous stress history of the soil has a significant effect on the estimated magnitude of settlements.



General Approach to Settlement Analysis

Approximately 3,600 metres of fill embankment would be constructed over alluvium associated with the Myall River floodplain. The soils are variable. Where they are predominantly sand, the fill should settle rapidly as the embankments are constructed. Where the foundation is clay, some settlement would occur during construction as the embankment surcharge is applied, but a significant proportion of the settlement could continue following embankment construction.

Fill embankments constructed on soft to firm clay foundations would be subject to settlement comprising:

elastic, primary consolidation and secondary consolidation settlement of the foundation soils;

internal compression within the fill embankment, due to self-weight (creep); and

settlement of fill material caused by saturation of the fill on subsidence into the soft foundations, flooding and/or surface water infiltration. This settlement can become significant when the void ratio of the compacted fill is greater than 5 percent.

Site investigations indicate that most of the alluvial soils are made up of sands or stiff to very stiff clays, and it is expected that elastic settlement would be the significant component of total settlements.

Where the embankment fill may be constructed on very soft, organic silty clay, primary and secondary consolidation settlement is expected to continue after embankment construction and could be excessive. Two-way drainage of the very soft clay layer was considered appropriate based on the subsoil conditions encountered in the investigation. Surcharge loading of embankments would reduce secondary consolidation.

The analysis has addressed the settlement associated with the foundation soils and not specifically the internal settlement within the embankment fill, which is considered to be minor in comparison. There is no established theory to assess the long-term compression of the embankment itself. The likely mechanism is thought to be due to crushing and rearrangement of soil/rock particles under its own weight, as well as change of environment such as moisture content and temperature. The degree of compression is dependent on the type of fill, compaction during construction and height of embankment.

Settlement Analysis Results

A construction program is required to estimate residual consolidation settlement that would occur after pavement construction is completed. On a large earthworks project the average rate of fill placement would be up to 2 metres per month and the period from start of fill placement to end of pavement construction would be about 12 months.



The results of preliminary settlement analyses, as shown in Table 4.16, indicate that the total primary consolidation settlement of the embankment at the Myall River Bridge approaches is about 0.7 metres and about 0.8 metres (south side and north side respectively). Consolidation is anticipated to be substantially complete after about 2 years and 3 years respectively. After a 12 month construction period, the residual consolidation settlement would be about 0.1 metres. Combined with secondary consolidation and internal creep settlement, post construction settlement at the Myall River bridge approach embankments are excessive in terms of the likely performance criteria.

Table 4.16: Results of Settlement Analysis

Calculated Settlement underDesign Embankment Height

(millimetres)

Consolidation Fill

Station(metres)

Structure

Design Fill Height (metres)


Elastic Primary Secondary

1 92100 No structures 2.5 1.1 metre sandy silt to silty clay, stiff to very stiff.

<5 -

2 94820 Southern interchange overpass

11 4 metre silty clay, firm; 4 metre sandy clay, firm; 9.0 metre clayey sand

100 100 30

95550 Myall River Bridge (South)

9 1.5 metre silty clay, soft; 2.0 metre organic clay, very soft; 9.0 metre sand

220 650 32

95700 Myall River Bridge (North)

8.5 2.0 m silty clay, soft; 2.7 m organic clay, very soft; 3.0 m sand

295 745 43

3 97480 Underpass 11 1.5 metre gravel/sand, loose; silty clay, very stiff

10 - -

4 99190 Underpass 7 2 metre clay, soft; 2 metre clayey sand/ gravelly sand, very stiff

90 110 7


98480 Overpass 17 1 metre silty clay, firm to very stiff

20 - -



The 11 metres high approach embankment to the overpass at the southern interchange is estimated to settle about 0.1 metres due to primary consolidation that would continue for about three years. At the end of a 12 month construction period when the one metre surcharge is removed the residual consolidation settlement is estimated to be negligible.

In Fill 4 (Station 99190), total consolidation settlement is calculated to be about 0.1 metres and this is predicted to be substantially completed within about 18 months. At the end of a 12 month construction period the residual consolidation settlement is estimated to be negligible after the 1 metre surcharge is removed.

The outputs from the settlement analysis are provided in Table 4.16.

Ground Treatment to Mitigate Settlement

At Myall River

Consolidation settlement at the proposed Myall River bridge is estimated to continue beyond the construction phase. Combined with secondary consolidation and internal creep, the total residual settlement is estimated to exceed the adopted performance criteria and some form of ground treatment would be required.

Typical methods of mitigating the effects of settlement include:

use of light weight fill (eg flyash, polystyrene);

bridging the surface with gravel and/or a geotextile material;

reinforcing the soil foundation (e.g. stone columns, piles); and

pre-loading and/or surcharging the embankment and foundation soils to induce a significant proportion of settlement before constructing the road pavement.

Pre-loading and/or surcharge is considered to be the most suitable option but analysis indicates that a 2 metre surcharge would be required for one year on the south side and 1.5 years on the south and north side respectively. A further increase in the height of the surcharge does not effectively increase the rate of settlement and but increases the risk of instability during construction. Surcharge also has the benefit of reducing secondary consolidation and internal creep settlements.

If programme or staging constraints necessitate shorter construction periods and do not allow this period of surcharge, a piled embankment is considered to be the next most viable option. This method has been used successfully during the construction of other sections of the Pacific Highway. Structural support of the fill would be provided by closely spaced driven piles with small pile caps overlain by a reinforced granular fill mattress. An upper level load transfer mat would be needed to reduce differential settlement effects and provide a transition zone to meet pavement geometric requirements.



The installation of wick drains over such a short length of embankment (possibly less than 20 metres each side of the river) in a relatively thin compressible layer was not considered to be a cost-effective option.

The removal of the soft soil from within the footprint of the embankments across the floodplain would probably require treatment of acid sulphate soils. The high groundwater may also make excavation difficult. Removal of the soft soils was therefore not considered to be viable.

Lightweight fill such as fly ash or polystyrene has been used on other highway projects elsewhere (for example, Port of Brisbane Motorway, F3 Freeway extension — Leneghans Drive, about 146 kilometres north of Sydney). The source of materials, cost and track record would need further consideration before this method could be considered.

At Other Locations

The investigations across the Myall River floodplain (Fill 2) found local areas where the surface soils (up to 2 metres deep) are relatively soft. The proposed embankment height is up to 7 metres. A nominal 1 metre surcharge should be applied along the length of the floodplain and remain in place for about one month to ensure primary consolidation of these local areas is substantially complete by the end of construction and to minimise the differential settlements. Further investigation would identify the extent and properties of these soft areas and may reduce the thickness of surcharge and duration of loading. Removal of the soft areas is probably not a viable option because of the presence of possible acid sulphate soils.

Fill 1 would be partially constructed over the embankment of the existing Pacific Highway and partly over natural ground. The ground beneath the existing embankments, therefore, has a different stress history to that of the natural ground and would respond differently when subjected to loads imposed by the new embankment. A surcharge about 1 metre high should be applied to the section of embankment founded on natural ground to minimise the risk of differential settlement caused by the differing ground conditions and embankment heights.

4.6.3 Stability of Fill Embankments

Design Criteria and Assumptions

The following criteria were adopted in the analysis of embankment stability. The criteria are consistent with criteria adopted on similar highway projects and published information (for example, Duncan 2000).

short term stability with a minimum FoS (factor of safety) of 1.2 (limit equilibrium analysis);

long term stability (excluding seismic loading) with a minimum factor of safety FoS of 1.5; and.



long term stability (including seismic loading) with a minimum factor of safety FoS of 1.1.

Design assumptions included:

stability models for the fills with a nominal 10 kilopascal (kPa) distributed load (surcharge) applied at the crest of the slope to simulate traffic loading within the carriageways and the embankment crests;

the groundwater level being at ground surface level for stability analysis across the Myall River floodplain;

a tension crack 2 metres deep and filled with water;

all embankments with batter slopes are constructed at 2 horizontal:1 vertical; and

a horizontal acceleration coefficient of 0.12g (gravity) used to model earthquake loading. This value was adopted from Minimum Design Loads on Structures, Part 4: Earthquake Loads, AS1170.4 (Standards Australia) 1993.

Analysis and Design

Stability analyses were undertaken at selected locations along the fill embankments assuming geotechnical models that are representative of worst case conditions (embankment height and ground conditions). These locations correspond to the estimated critical settlement locations.

Where analyses indicated the design criteria stated above had not been met, mitigation measures such as the use of reinforcement across the base of the embankment and/or staged construction were incorporated into the stability analyses.

Table 4.17 summarises the factors of safety calculated for embankments constructed to the proposed design height on the inferred foundation conditions. The analysis highlights potential instability during construction of embankments adjacent to the Myall River.



Table 4.17: Summary of Stability Analyses at Design Embankment Height

Calculated Factor of Safety at Design

Embankment Height

Fill Station (approx. metres)

Structure Design Fill Height (metres)


Short1 Term

Long Term

Long Term plus

Earthquake loads

1 92100 No structures 3 1.1 metre sandy silt to silty clay, stiff to very stiff.

>3 1.6 1.4

94550 Southern interchange overpass

11 4 metre silty clay, firm; 4 metre sandy clay, firm; 9 metre clayey sand

1.3 1.5 1.3

95495 Myall River Bridge

7.5 1.5 metre silty clay, soft; 2.0 metre organic clay, very soft; 9.0 metre sand

<1.0 1.8 1.6

2

95705 Myall River Bridge

10 2.0 metre silty clay, soft; 2.7 metre organic clay, very soft; 3.0 metre sand

<1.0 1.9 1.6

3 97400 Underpass 4.5 1.5 metre gravel/ sand, loose; silty clay, very stiff

>1.6 >1.6 >1.4

4 99200 Underpass 5 2 metre clay, soft; 2 metre clayey sand/gravelly sand, very stiff

1.2 1.5 1.3


98500 Overpasses (2 bridges)

6 1 metre silty clay, firm; to very stiff

1.6 1.5 1.3

1. Bold result indicates does not comply with design criteria.

For areas identified as requiring stabilisation it is proposed that staged construction and/or basal reinforcement is adopted. Strains in the reinforcement should be limited to about 5 percent to prevent the soil undergoing strain softening before the reinforcement is fully loaded. More detailed finite element analysis may be required to predict forces developed in the geotextile during final design.

The purpose of staged construction is to reduce the risk of excessively high excess pore water pressures developing in the foundation soil. A pause in construction at predetermined fill heights allows the excess pore water pressure to dissipate with a corresponding gain in shear strength in the underlying foundation soils.



Instrumentation should be installed in soft fill foundations to and monitor pore pressures and settlements during and following embankment construction to confirm strength gain in the foundations before the next stage of fill is placed and to confirm the rate of settlement. The removal of surcharge loads would depend on the monitored results.

4.6.4 Construction on Floodplains

Construction Traffic Access

The soft compressible soil across the floodplain sections of the route alignment will present problems for use by construction equipment.

Generally, a surface crust lies along most of the floodplain sections of the route with the exception of some low lying swampy areas in Fill 2. The presence and strength of the surface crust could be weather dependent. In periods of dry weather, the surface crust is likely to be quite pronounced and may enable the floodplain to be used by conventional light construction equipment. However, during periods of wet weather, the surface crust may exhibit a marked decrease in strength and conditions are likely to be poor for even very light or track mounted equipment.

During the site investigations, certain locations in Fill 2 were not useable by rubber tyred vehicles during periods of inclement weather. If such conditions exist at the time of construction, it is expected that a bridging layer will be required for access across much of the floodplain. It is also expected that some of the existing subgrade will not achieve the required level of proof rolling prior to embankment construction without a bridging layer.

Subgrade Preparation

Foundation preparation at Fills can be divided into embankments located on the alluvial floodplains and those located on colluvium or residual soils.

Floodplains

Embankments on floodplains include Fills 1 and 2 and part of Fill 4 between Station 99600 and 100000. Fill 3 is located on a thin horizon of stiff colluvium and/or residual clay soil. Due to the presence of potential acid sulphate soils in the floodplain area, disturbance of these soils should be minimised and undertaken in accordance with the Acid Sulphate Management Plan (Parsons Brinckerhoff 2002a).

Approaches recommended for areas of poor trafficability are:

mowing of vegetation to ground level leaving the topsoil and root mat in place; and

placement of a layer of non-woven type geotextile.



Depending on the subgrade conditions and the embankment height, the first layer may be embankment fill. If a soft foundation is encountered, a bridging layer comprising of a clean free-draining granular material such as select fill would be required. The thickness of the layer should be sufficient to produce a firm base for compaction. Rock fill bridging material should be separated from general fill by a geotextile or filter layer to prevent migration of the general fill into the bridging layer.

The contractor on site would select the most appropriate method of subgrade preparation, having regard to the climatic conditions, specification and earthwork plan requirements and the construction equipment available.

The minimum embankment thickness required beneath the pavement to provide a suitable base for acceptable pavement construction across the floodplain is likely to range from 0.5–1.0 metres depending on the subgrade strength and weather conditions. The required bridging layer thickness would increase markedly if excavation and removal of the near surface crust is proposed.

Filling could continue to specification following establishment of a firm base by the placement of the general bridging layer.

Unsuitable materials such as topsoil and other soft compressible materials should be removed before embankment materials are placed in areas unaffected by acid sulphate soils; or the overlying root mat and grass cover maintained as part of the bridging layer depending on conditions at time of construction. Where the subgrade is steeper than 3 percent, terraces should be excavated into the slope so that the embankment is keyed in to the foundation in accordance with the earthworks specification.

Colluvium/Residual Soil Areas

For fill over colluvium the following approach is suggested:

remove vegetation and excavate horizontal benches as necessary to key fill into site;

prepare and compact the surface;

place a layer of woven type geotextile;

place drainage material (coarse granular aggregate) with woven geotextile above; and

place select fill material in layers.



4.7 Bridge Structures

4.7.1 Southern Interchange

The southern interchange is located about midway across the Myall River floodplain where ground conditions are expected to comprise alluvial deposits to a depth of approximately 12 metres overlying residual soils and sandstone/siltstone from a depth of approximately 21 metres.

The proposed structure consists of a two lane, two span (28 metres and 33 metres) concrete bridge over the proposed Upgrade.

Pile types adopted at this site could be either driven reinforced concrete piles or bored piles socketed in to the underlying rock. Driven piles have the advantage that no soil is excavated that may require treatment for potential acid sulphate soils. Testing of the driven pile capacity is readily carried out during installation allowing more efficient design. Excavation for bored piles would penetrate sand below the groundwater and would require either full depth casing or support with a drilling fluid (such as bentonite).

Piles would need to be installed after the surcharge has been removed from the approach embankments and primary settlement is complete. The fill should be pre-bored to avoid damage by pile driving.

4.7.2 Myall River Bridge

The Myall River is located on the north eastern side of a 2.8 kilometre wide floodplain. The watercourse is some 65 metres wide and the river channel is about 9 metres deep at the location of the proposed bridge location. The bridge would have six spans (each 35 metres) with two sets of piers located in the Myall River.

The subsurface investigation indicated alluvial sediments to a depth of 7–12 metres below the riverbed, overlying residual soil and high strength sandstone from approximately 10–16 metres. An appropriate foundation may consist of steel tubular piles driven to rock then a rock socket formed into the sandstone. Further borehole investigation across the river at the proposed pier locations is needed to confirm the depth to sandstone and identify an appropriate footing type and founding levels.

Driven reinforced concrete piles may be appropriate at the abutments, as bored piles would possibly require treatment and disposal of acid sulphate soils. Alternatively, steel tubular piles driven to rock could be adopted.

The impact of sulphates on reinforced concrete driven pile durability can be minimised by using the procedures outlined in the Australian Standards and RTA guidelines. The design of the existing bridge upstream adopted 20 inch (500 millimetre) diameter driven concrete piles.



4.7.3 Bombah Point Road Overpass

The proposed two-lane overpass would be along Myall Road leading to Bombah Point Road. The two-lane overpass would consist of a two-span (34 metres and 31 metres) concrete bridge over the proposed Upgrade.

The overpass is located at Station 95925 in Cut 2. The cut would be through sandstone. The subsurface profile is expected to comprise stiff to very stiff silty clay over sandstone of varying weathering (extremely to slightly weathered) with slightly weathered to fresh, very high strength sandstone from approximately 6 metres. It is anticipated that the abutments to the bridge would be founded on spread footings or short bored piles.

4.7.4 Mountain Access Overpass

The single lane overpass is located in Cut 3 where the subsurface conditions comprise 2 metres of residual soil (firm to hard clay) overlying highly to extremely weathered siltstone. The proposed concrete bridge would have two spans (27 metres and 30 metres). It is anticipated that a spread footing founded on the weathered siltstone could be adopted. It may be necessary to bore short piles if the depth of weathering or the structure of the siltstone (orientation of bedding, joints or other defects) is unfavourable.

4.7.5 Stuart Street Underpass

The proposed underpass adjacent to Stuart Street is located in Fill 3, which is generally underlain by very stiff silty clay (colluvium). This narrow pedestrian and wildlife underpass would be a bridge structure.

4.7.6 Northern Interchange

The proposed interchange consists of two single-lane, two-span (south: 22.5 metres and 21.5 metres; north: 24 metres and 23 metres) bridges.

In general terms the geology in the area of the northern interchange comprises fill and colluvial soils to depths to 3 metres. Underlying the soil is either sandstone (Bulahdelah Formation), sandstone/conglomerate (Markwell Coal Measures), basalt (Burdekins Gap Basalt Member), ignibrite/tuff/breccia (Sams Road Rhyolite Member) or conglomerate (Muirs Creek Conglomerate).

The geology around the northern interchange was found to be complex and often masked by the colluvium. It is anticipated that the bridges would be founded on spread footings or short bored piles. Further investigation at the locations of the bridge footings would be required.



4.7.7 Underpass to the Waste Facility

The underpass would be located in the northern section of Fill 4 where the embankments would be on alluvium. The proposed structure consists of two single-span 15.5 metre concrete bridges over the service road.

The subsurface profile would comprise alluvium grading from soft to firm sandy clay to very dense clayey gravely sand overlying residual soil (hard silty clay) and then highly weathered sandstone.

Foundations similar to that adopted for the southern interchange are considered appropriate.

4.7.8 Frys Creek Bridge

The existing bridge for the northbound carriageway would be demolished and a new concrete bridge constructed across Frys Creek. The new bridge would consist of two 16 metre spans.

The subsurface investigation encountered 5 metres of firm/loose alluvium overlying 1 metre of residual soil, then sandstone. The sandstone grades from extremely weathered, extremely low strength to extremely/highly weathered, low strength at approximately 13.5 metres below existing ground surface.

Driven precast concrete piles are considered appropriate for the abutments and the central pier.

4.8 Acid Sulphate Soils

In the Preferred Route Option Report (PPK 2001), the alluvial plains in the vicinity of the proposed Myall River crossing were assessed as areas of high probability of acid sulphate occurrence within 1 metre of the ground surface. The alluvial backplain and backswamp area was assessed as high probability of acid sulphate soil occurrence 1–3 metres below ground surface. Soil testing in the alluvial plain landform found strong positive indications of potential acid sulphate soils close to the surface.

Following this initial study an Acid Sulphate Soil Investigation and Management Plan was carried out (Parsons Brinckerhoff 2002a). This work comprised additional subsurface investigation from which samples were collected and screen tested and selected samples laboratory tested. Groundwater samples were also taken.

The results of this additional subsurface investigation indicated a high probability of potential acid sulphate soils at the backswamp area between Station 95150 and Station 95400 and at the Myall River bridge abutment. Laboratory testing confirmed this. Groundwater and surface water monitoring indicate that oxidation of pyritic material is not occurring at present. The Acid Sulphate Soil Risk Map is shown ion Figure 2.5.



The Acid Sulphate Soils (ASS) Management Plan (Parsons Brinckerhoff 2002a) recommended that stripped topsoil be stockpiled and treated with lime. It was also recommended that clay foundations should not be exposed for longer than 24 hours; and lime should be spread over the foundation prior to placement of embankment fill.

4.9 Acid Sulphate Rock

While it does not affect the stability or settlement of the proposed embankments, the occurrence of acid rock at the source of material from which the embankments may be constructed could affect the quantities of suitable construction fill available and the methods of construction adopted (for example, zoned embankments may be constructed with acid sulphate soils as an inner core though it does not affect the stability or settlement of the proposed embankments).

During the Geotechnical Investigation for Route Selection (PPK 2001) rock samples were tested for acid producing potential. The test results indicated a range from non-acid to potentially strongly acid producing rock. Samples indicated moderate and strong acid producing potential on the lower slopes of Bulahdelah (Alum) Mountain north of Ann Street/Bombah Point Road, from the Bulahdelah Formation geological unit through which the preferred route would be cut.

A sample from the colluvial area was also designated as potentially acid forming. It is likely that mixing resulting from the excavation, haul and placing would reduce the risk of fill containing locally high concentrations of acid sulphate rock.

4.10 Contaminated Soils

A desk study conducted during the route selection process identified sites with potentially contaminating land use activities. These included the old waste treatment plant, the former alunite mine, an old sawmill and the golf course. Although none of these sites would be within fill zones, contamination may could affect the volumes of suitable materials available for embankment construction and/or affect the construction methods adopted.

Further testing for contamination at the former alunite mine, sawmill and wastewater plant was carried out as part of the route development work. The study concluded that:

no remedial works are required at the alunite mine site;

minor remedial work is recommended for the sawmill before or during construction; and

no remedial work is recommended for the waste water treatment plant.



4.11 Erosion Hazard

The erosion hazards associated with the proposed Upgrade are described below. A detailed discussion of the erosion and sedimentation management strategies is provided in Technical Paper 8 — Water.

4.11.1 Hill crests and ridges

The NSW Soil Data System indicates that there are four soil profiles within this terrain unit for erosion hazard. Two of these have been rated with a very high erosion hazard, one of the other profiles is rated as moderate and one is slight.

4.11.2 Slopes

The NSW Soil Data System indicates that there are two soil profiles within this terrain unit for erosion hazard. Both of these profiles have been rated with a slight erosion hazard.

4.11.3 Alluvial Plains

The NSW Soil Data System indicates that there are seven soil profiles within this terrain unit for erosion hazard. All of these profiles have been rated with a slight erosion hazard.

4.11.4 Backswamps and Backplains

The NSW Soil Data System indicates that there are two soil profiles within this terrain unit for erosion hazard. One of these profiles has been rated with a slight erosion hazard and the other with a high erosion hazard.

4.11.5 Management

One-third of the preferred route is in the alluvial plains terrain unit (with backswamp and backplain contact west of the river). The northern two-thirds comprise slopes and hill crests and ridges terrain units. The NSW Soil Data System profiles within the alluvial plains and slopes terrain units have a slight erosion hazard. The backswamps and backplains and hill crests and ridges units contain soil profiles rated with high and very high erosion hazards.

Areas of more sandy soils are potentially more susceptible to erosion. In areas of cut, the exposed batter after construction is generally expected to comprise extremely to highly weathered sedimentary rock, interbedded with clay seams. Such material will be susceptible to erosion.


Impact Assessment and Mitigation Technical Paper 11

5. Impact Assessment and Mitigation

5.1 Cuttings

The preferred route would require road cuttings up to 25 metres in height. The objectives of the cutting design were to achieve batter slopes that:

present a design with low risk of instability or disruption to highway operations by rockfalls;

satisfy requirements of the RTA; and

minimise need for external support.

Cuttings in similar materials in both the adjacent Bulahdelah to Coolongolook section and the existing local Pacific Highway demonstrate the potential impact of adversely oriented joints in the rock mass and the influence of deep weathering profiles on the cutting design. Therefore, to minimise the potential impact and reduce the risk of instability to an acceptable level, appropriate cut profiles have been provided in Section 4.2 with particular consideration given to Cut 4 through colluvium material. Measures to provide batter protection and stabilisation have been presented in Section 4.3.

Impacts can be reduced for all cuts by minimising excavation depths. The quantity of material excavated can be further reduced by constructing cut batters as steep as possible. Current RTA requirements are for minimum bench widths of 4 metres spaced at the maximum batter height requirement of 7 metres. The impact of the cuts could be reduced by reducing the widths of the benches to 3 metres and increasing the bench intervals to 10 metres. These steeper batters would be subject to further detailed geotechnical investigation and confirmation and assessment of earthworks quantities.



5.2 Embankments

The investigations and analysis undertaken indicated potential concerns relating to the presence of localised areas of very soft compressible soils adjacent to the Myall River. These soils may extend under the approach embankments to the proposed Myall River bridge. The site investigations for the design stage should aim to determine the extent of these very soft soils. The presence of these soils has an impact on the stability, settlement and extent of ground treatment required. Assuming that the very soft soil extends beneath the embankments, staged construction would be required to reduce instability and a 3 metre surcharge would need to be applied for a period of up to 18 months to minimise post construction consolidation settlements. Alternatively, if the construction program does not permit such a long surcharge period, a short (less than 50 metres) total length of piled embankment is considered the most appropriate alternative solution.

Investigations across the Myall River floodplain (Fills 1, 2 and 4) indicate local areas where the surface soils are relatively soft. In these areas the proposed embankment height would be up to 7 metres. A nominal 1 metre surcharge should be applied to ensure primary consolidation of these local areas is substantially complete by the end of construction and to minimise the risk of differential settlement between sections of embankment founded on soft soils and those founded on stiff soils. Further investigation would identify the extent and properties of these soft areas and may reduce the extent of surcharge and the duration of loading. Removal of the soft areas is probably not a viable option because of the possible presence of soils may be acid sulphate soils.

Embankments constructed partly over the embankment of the existing Pacific Highway and partly over natural ground, may induce differential settlement over the differing ground conditions. Therefore, a surcharge about 1 metre in height should be applied to the section of embankment founded on natural ground.

It is expected that embankments at other locations could be constructed without the need for extensive ground treatment to conform to the adopted design criteria.

The issues addressed in this technical paper have been incorporated in the concept design developed as part of the environmental impact process.

Additional investigations would be required at the design stage to determine the extent of soft soils. These would be predominantly in areas where access may be difficult and significant disturbance may occur.


Impact Assessment and Mitigation Technical Paper 11

5.3 Acid Sulphate Soil and Acid Rock

The proposed Upgrade would involve excavation activities, alterations to surface and groundwater flows, and potential lowering of groundwater levels, particularly in the vicinity of the road alignment. As a result the proposal has the potential to oxidise potential acid sulphate soils, generating acid, and disturb actual acid sulphate soils.

Potential impacts would include groundwater chemistry changes such as lowered groundwater pH, increased heavy metals in solution, increased aluminium in solution and raised total dissolved solids. Such groundwater discharges to the Myall River, and associated tributaries and wetlands, could result in environmental harm in these sensitive environments. However, the presence of acid sulphate soils does not preclude development, as the issue can be managed via an appropriate Acid Sulphate Management Plan and impacts on many Pacific Highway Office projects under this approach have been minimal.

The management plan would address:

background trends — pre-construction monitoring of groundwater chemistry would establish the background trend and natural variability of the system. Natural acid tolerant species exist in this environment, thus site specific criteria are required in preference to guideline levels and pH control would be aimed at maintaining the natural pH condition;

soil pH — the soils are potentially acid forming and excavated material would need treatment with agricultural lime, containment in bunded areas to prevent leachate escape and testing to assess pH and rate of acid generation (if any). The results of testing would be used to assess the ratios that are required for treatment;

a practical water quality management program using collected pre-construction monitoring results and construction water quality monitoring. Leachate from excavated acid material would be captured. Chemical tests would assess whether the leachate is affected by acid sulphate soils and the level of treatment that might be necessary; and

Groundwater pH —– deviations from long-term trends outside natural variations may require treatment to restore groundwater chemistry. These would be assessed by monitoring before, during and after the development. Groundwater pH and indicators of actual acid sulphate soil impacts on groundwater chemistry should be monitored.

5.4 Contaminated Soils

Potential contamination issues do not appear to be a major influence on the project. It is considered unlikely that soil contamination issues would significantly affect construction activities.



Should localised concentrations of contaminants be encountered during the construction phase, a number of remedial or management options are available. The remedial or management option selected would depend on several factors including the type of contamination encountered, time frame for remedial works and budget constraints. Typical remedial options include:

excavation, on-site remediation and reuse;

excavation and off site disposal; and

excavation and on-site containment.

5.5 Soil Erosion and Sedimentation

Measurements of the laboratory Emerson Class Number for soil samples recovered from proposed cut areas indicate that the soils within the alluvial plains and slopes terrain units have a slight erosion hazard. The backswamps and backplains, and hill crests and ridges units contain soil profiles that have high and very high erosion hazards. Such soils commonly have a low to medium erosion hazard when appropriate vegetation cover or other form of protection is provided. The high intensity rainfall conditions encountered in the Bulahdelah region require cuts and embankments to be protected at all times.

Soil erosion and sedimentation can be managed with an appropriate soil and water management plan. A detailed discussion is provided in Technical Paper 8 — Water.


Further Investigation Technical Paper 11

6. Further Investigation

A detailed geotechnical investigation would be carried out at the detailed design stage to confirm and amplify the results, comments and recommendations provided in this and associated reports.

The investigations and analysis undertaken have indicated potential concerns relating to the presence of areas of very soft compressible soils adjacent to the Myall River and associated alluvial plains. The presence of these soils would have an impact on the stability, settlement and extent of ground treatment required.

Particular attention would have to be given to further investigations where embankments would be constructed on soft compressible soils. Further investigation of the soft soils would be undertaken to confirm the strength and compressibility characteristics/parameters adopted, and construction staging requirements.

The following actions would be undertaken in areas of cut and colluvium:

additional inspection of boulders immediately upslope of the cutting before or during excavation works;

regular ongoing inspections of the cut face during construction and final trimming of batter slopes;

ongoing monitoring of ground movements and groundwater levels to be continued until after completion of the road upgrade; and

reassessment of risk on a bi-annual basis, for at least five years. The need for further monitoring should be determined based on the outcome of this monitoring program.

Further investigation would also have to undertaken at each of the proposed bridge footings.

During the construction of the road, close supervision of the earthworks, construction of retaining walls and inspection of the footing foundations by an experienced geotechnical engineer or geotechnical person would be required.


References Technical Paper 11

References Australian Geomechanics Society Sub-Committee on Landslide Risk Management 2002 Landslide Risk Management Concepts and Guidelines, Australian Geomechanics, Vol 37, n2, May 2002.

Central Mapping Authority of New South Wales (CMA) 1985 Bulahdelah, Reference 9333-3-S, 1:25,000 scale.

Department of Conservation and Land Management 1992 A Guide for the Interpretation of Soil Test Results.

Department of Land and Water Conservation 1997 Bulahdelah Acid Sulphate Soils Risk Map – Edition Two, 1:25,000 scale.

Duncan J. M 2000 Factors of Safety and Reliability in Geotechnical Engineering, Journal of Geotechnical Engineering ASCE Vol. 126, No. 4, pp307-316.

Environment Protection Authority 1988 Managing Urban Stormwater — Construction Activities.

NSW Department of Mineral Resources 1991 1:100 000 Geological Series Sheet 9333 (Edition 1), Bulahdelah.

NSW Department of Mineral Resources 1999 1:1 500 000 Mineral Projects of New South Wales.

PlanningNSW 2002 Hazardous Industry Planning Advisory Paper Number 4 — Risk Criteria for Land Use Safety Planning.

PPK Environment and Infrastructure 2001 Pacific Highway, Bulahdelah Upgrade, Project Development and Preferred Route Option Report, report to RTA, reference 58L320A/083.PR_5406 Rev D, July 2001.

PPK Environment and Infrastructure 2001 Pacific Highway Upgrade, Bulahdelah – Geotechnical Investigation for Route Selection, report to RTA, reference 58L320A/070.PR_973 Rev B, August 2001.

PPK Environment and Infrastructure 2002a Acid Sulphate Soil Investigation and Management Plan, Pacific Highway Upgrade, Bulahdelah, report to RTA, reference 2122155A PR_0873, July 2002.

Parsons Brinckerhoff 2002b Bulahdelah Upgrade: Geology of Northern Interchange, report to RTA, reference 2122155A PR_4259 RevA November 2002.

Parsons Brinckerhoff 2003b Contamination Assessment, Former Alunite Mine, Sawmill and Wastewater Treatment Plant, Bulahdelah, report to RTA, reference 2122155A PR_1008, March 2003.

58L320A.070 11 - Topography, Geology & Soils Final.doc PARSONS BRINCKERHOFF Page R-1


Parsons Brinckerhoff 2004a, Upgrade of the Pacific Highway at Bulahdelah, Report on Colluvium Area Stability, report to RTA, reference 2122155A PR_3137 Rev C, 21 January 2004.

Parsons Brinckerhoff 2004b, Upgrade of the Pacific Highway at Bulahdelah. Geotechnical Investigation Report for Preferred Route, report to RTA, reference 2122155A PR_4339 Rev B, May 2004.

Roads and Traffic Authority 2003 QA Specification R44 — Earthworks, Roads and Traffic Authority, December 2003.

Stewart I.E, Baynes F.J and Lee I.K 2002 The RTA Guide to Slope Risk Assessment — Australian Geomechanics, Vol 37, n2, May 2002.

Standards Australia 1993 Australian Standard Minimum Design Loads on Structures, Part 4: Earthquake Loads, AS1170.4.

URS 2003 Final Report: Independent Review of GHD-Longmac Report – Lawrence Hargrave Drive, Wollongong, report to RTA, reference 25191-019, 26 August 2003.

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