Earthwork for Road Construction

EARTHWORK FOR ROAD EMBANKMENTS

Presentation by

Dr. Vasant G. Havanagi

INTRODUCTION

• Pavement failures due to settlement of embankment fill and subgrade

• Need for suitable fill materials and proper quality control during execution

• Adoption of MORTH specifications

Types of soil in IndiaTypes of soil in India

Alluvial soils Fine sands Coastal soils BC soils Red gravelly soils

Types of soil in IndiaTypes of soil in India

Desirable properties of Desirable properties of soilsoil

Stability Incompressibility Permanency of strength Minimum changes in volume &

stability Good drainage Ease of compaction

Undesirable types of Undesirable types of soilsoil

Highly plastic soils Soils which favour capillary rise of water Frost susceptible soils Organic and sulphatic soils Permissible limits

Sodium sulphate - 0.5 per cent maximum Organic matter - 1.0 per cent maximum

EARTHWORK FOR EMBANKMENT/SUBGRADE

• SUITABILITY OF MATERIALSFree from peat, perishable and other organic

materialShould not be spontaneously combustibleLL 70, PI 45With salts are not suitableFree Swell Index 50 % should not be used Total sulphate content ( 0.5 %) must be avoided

within 500mm of metallic itemsBorrow pits – max.depth 1.5m, offset from toe min.

10m.

EARTHWORK FOR EMBANKMENT/SUBGRADE (Contd.)

• SIZE OF MATERIAL Size of coarse material 75 mm in

embankment fill 50 mm in subgrade Max. particle size 2/3 of compacted

layer thickness

Density requirements for Embankment and Subgrade (Section 305.2.1.5)

S.No. Type of work Maximum laboratory dryunit weight when tested as

per IS: 2720 (Part 8)

1. Embankments up to 3 metresheight, not subjected toextensive flooding

Not less than 15.2 kN/cu.m

2. Embankments exceeding 3metres height orembankments of any heightsubject to long periods ofinundation


3. Subgrade and earthenshoulders/verges/backfill


Construction operations (MORTH specifications-305.3)

• Clearing and grubbing• Setting out• Dewatering• Stripping and storing top soil• Compacting ground supporting

embankment/subgarde.• Spreading material and bringing to

appropriate moisture content.


• Spreading of material in layers and

bringing to appropriate moisture content. Max. compacted thickness = 20 cm Moisture content (-2 % + 1% of OMC)

Expansive soils (@ OMC or on wet side of optimum) Pan drying method Oven drying method Speedy moisture meter (AASHTO T-217) Microwave oven method


• Compaction Smooth wheel rollers Sheep foot rollers Pneumatic tyred rollers Vibratory rollers

• Other compacting equipments Small vibratory rollers Plate vibrators Rammers

Objectives of soil compactionObjectives of soil compaction

• Increase in strength

• Reduction in compressibility

• Reduction in tendency for subsequent changes in moisture content

• Reduction in erodability

• Reduction in frost susceptibility

Factors influencing Factors influencing compactioncompaction

• Type of soil

– Gradation (Well-graded/Uniformly-graded)

– Clayey soil

– Silty soil

– Sandy soil

– Gravel

Moisture-density relationship for Moisture-density relationship for different types of soilsdifferent types of soils

Factors influencing Factors influencing compactioncompaction (contd.)

• Moisture content– Dry of optimum

– Optimum

– Wet side of optimum

• Compactive effort– Energy applied per unit weight of soil

• Weight of rammer, height of fall, number of blows

• Weight of roller, number of passes

Moisture-density relationshipMoisture-density relationship

Effect of compaction on soil Effect of compaction on soil propertiesproperties

• Unconfined compressive strength

• California Bearing Ratio (C.B.R)

– Unsoaked C.B.R

– Soaked C.B.R

• Permeability

• Settlement

Relation between density and unconfined compressive strengthRelation between density and unconfined compressive strength

Relation between density and CBR for a heavy clayRelation between density and CBR for a heavy clay

Variation of CBR of silty clay with Variation of CBR of silty clay with compactioncompaction

Compaction-permeability relation for clayCompaction-permeability relation for clay

Effect soil content & size of aggregate on Effect soil content & size of aggregate on CBRCBR

Field compacting Field compacting machinerymachinery (Contd)

• Smooth wheel roller

– Used for compacting subgrade, base and asphaltic surfaces

– Suitable for compacting gravels, sand, and crushed rock

– 8 to 10 tonne rollers

– Appropriate speed of the roller should be 3 - 6 km/h.

Conceptual structure of compacted material using static roller


• Sheepsfoot roller

– Used in road and earthen dam works

– Suitable for compacting heavy clays and silty clays

– Important parameters affecting compaction• Weight of roller

• Area of each foot

• Number of foots/lugs in contact with the ground at any time

• Contact area of the foot


• Pneumatic tyred rollers

– Used for both earthwork and bituminous works

– Suitable for compacting cohesionless gravel,

sand and cohesive soils

– Important parameters affecting compaction• Tyre inflation pressure• Area of contact


• Vibratory rollers– Higher compaction level can be achieved with

minimum work

– Compaction can be done up to greater depths

– Output is many times more than conventional rollers

– Suitable for compacting sand and gravels

– Important parameters affecting compaction• Dead load

• Frequency

• Amplitude

• Area of contact

Vibratory Vibratory rollerroller

Conceptual structure of compacted material using vibratory roller

Effect of frequency on compactions of gravel

Density depth relationship with various compaction unit


• Vibratory plate compactors– Useful for small road works and narrow areas such as trench

backfilling

– Suitable for compacting thin layers

– Can be tractor-towed

• Rammers– Provide impact load

– Suitable for compacting small areas, back filling of trenches

in foundations

– Suitable for compacting cohesive as well as non-cohesive soils

– Operated manually (driven by petrol engines)

Small Small vibratory vibratory rollerroller

Plate Plate compactcompact

oror

Lift thickness during Lift thickness during compactioncompaction

• Depends on different factors

– Type of roller

– Weight of roller

– Type of soil

– Number of passes

– Prevailing moisture content

– Degree of compaction required

DozersDozers

JCB JCB (Backhoe (Backhoe cum cum Loader)Loader)

Motor Motor gradergrader

Tractor as Tractor as gradergrader

Tractor Tractor as as

ploughplough

Construction in urban areas

Need of survey of underlaying Cables, Water pipe lines, and Sewer lines etc. Shifting the same as per requirement.


Man hole in the centre of Compacted subgrade


• Field density control Core cutter method Sand replacement method Non-destructive methods, Nuclear density

gauge (AASHTO T-238, ASTM D-2922,D-3017)

• Relative compactionField dry density x 100

Laboratory density

Compaction requirements for embankment and subgrade (Table 300-2,MORTH specifications)

S.No. Type of work/material Relative compaction aspercentage of max. laboratory drydensiy as per IS: 2720 (Part 8)

1. Subgrade and earthenshoulders

Not less than 97

2. Embankment Not less than 95

3. Expansive clays

(a) Subgrade and500 mm portionjust below thesubgrade

(b) Remainingportion ofembankment

Not allowed

Not less than 90

Sl.No Test Relevant code

Frequency of test

1. Deleterious content IS:2720 : Part - 27

Min 2 tests per borrow area

2. Natural Moisture content IS:2720 : Part - 2

1 test / 250 m3

3. Gradation IS:2720 : Part - 4

2 tests / 3000 m3

4 Plasticity Index IS:2720 : Part - 5

2 tests / 3000 m3

5. Compaction tests IS:2720 : Part - 8

2 tests / 3000 m3

6. C.B.R IS:2720 : Part - 16

1 test / 3000 m3

7. FField density(a) Embankment (b) Subgrade/shoulders

IS:2720 : Part – 28

IS:2720: Part - 29

1 test / 1000 m2

1 test / 500 m2

Quality control tests and their frequencies (Section 903,MORTH)

QUALITY CONTROL (Contd.)

• Tolerances in surface levels in subgrade

+ 20 mm, -25 mm

• Acceptance crireria

Mean density should not be less than

specified density +

1.65 - 1.65 times the standard deviation

(No. of samples)0.5

EARTHWORK UNDER SPECIAL CONDITIONS (MORTH specifications 305.4)

• Compacting ground supporting Embankment/Subgrade

• Earthwork over existing road surface

• Earthwork for widening existing road embankment

• Embankment construction under water

EROSION CONTROL (MORTH SPECIFICATIONS 306 TO 308

• Common methods Turfing with sods Seeding and mulching with jute/geo netting

Special techniquesUse of geocellsSlopes in cohesionless sands and

black cotton soils

Erosion Control of Slopes

Use of Jute Geotextile

GEOCELL FOR SLOPE STABILIZATION AND EROSION CONTROL

CASE STUDIES

APPROACH EMBANKMENT FOR SECOND APPROACH EMBANKMENT FOR SECOND NIZAMUDDIN BRIDGE AT DELHINIZAMUDDIN BRIDGE AT DELHI


– Length of embankment - 1.8 km

– Height varies from 6 to 9 m

– Ash utilized - 1,50,000 cubic metre

– Embankment opened to traffic in 1998

– Instrumentation installed in the embankment showed very good performance

– Approximate savings due to usage of fly ash is about Rs.1.00 Crore

Approach Embankment for Nizamuddin Bridge Approach Embankment for Nizamuddin Bridge

SLOPE STABILITY ANALYSIS OF FLY ASH EMBANKMENTSLOPE STABILITY ANALYSIS OF FLY ASH EMBANKMENT(DIFFERENT SIDE COVER THICKNESS)(DIFFERENT SIDE COVER THICKNESS)

Details Factor of safety

Case I Case II

6 m high embankment,

1 m side cover throughout

1.5 m side cover throughout

2 m side cover upto mid height and remaining portion 1 m cover

2 m side cover throughout

--

1.30

1.42

1.48

1.05

1.20

1.36

1.41

Case I Fly ash saturated upto mid height

Case II Fly ash saturated upto top level

Spreading of pond ash

Compaction of pond ash

Second Nizamuddin Bridge Approach Embankment


Stone pitching for slope protection

Traffic plying on the embankment

PITCHING/REVETMENT OF SLOPES• Road embankment with stone, boulders• Stones in wire crates over a layer of granular

material (filter)-protection against river action.• Size and weight shall conform to clause 5.3.5.1 of

IRC:89• Min.weight of stone 40 kg.• Size of spalls min.25mm• Use of cement concrete blocks (M15) when

stones not available


Following instruments installed for monitoring performance of embankment

– Magnetic settlement gauges for settlement

– Pressure cells for base pressure

– Pore pressure transducers for pore water pressure measurement

INSTRUMENTATIONINSTRUMENTATION

Deatails of instrumentation


Installation of pressure cells

Installation of settlement gauge under progress


– No settlement of the embankment structure (fly ash fill)

– Development of negligible pore water pressure

INFERENCES FROM INSTRUMENTATION DATAINFERENCES FROM INSTRUMENTATION DATA

TECHNO-ECONOMIC ADVANTAGESTECHNO-ECONOMIC ADVANTAGES

• Direct saving of about Rs.One Crore in second Nizamuddin Bridge project for PWD

• Additional savings to Vidyut Board, saving of precious top soil

• In road projects savings to the extent of 15-20 per cent can be achieved

• Savings depend on cost of transportation of fly ash

USE OF POND ASH FOR ROAD USE OF POND ASH FOR ROAD EMBANKMENTEMBANKMENT

(FOUR-LANING WORK ON NH-6, DANKUNI TO KOLAGHAT, KM 17 TO 72, WEST BENGAL)

• Length of road - 60 km

• Height of embankment - 2 to 4 m

• Water logged conditions

• Soft sub-soil conditions

TYPICAL ROAD TYPICAL ROAD FEATURES/CONDITIONS OF THE FEATURES/CONDITIONS OF THE

PROPOSED ROADPROPOSED ROAD

Four-laning work on NH-6, Dankuni to Kolaghat,Four-laning work on NH-6, Dankuni to Kolaghat,

EXISTING CONDITION OF ROAD OTHER EXISTING CONDITION OF ROAD OTHER SIDESIDE


EXISTING CONDITION OF ROADEXISTING CONDITION OF ROAD


PRELIMINARY INVESTIGATION AND PRELIMINARY INVESTIGATION AND ASSESSMENT OF SITE CONDITIONSASSESSMENT OF SITE CONDITIONS

• Medium to High rainfall• Water table is high• Waterlogged conditions

• Subsoil generally weak– Silty clay or clayey soil up to 20 m depth– SPT values in the range of 2 to 5– c = 0.25 kg/cm2, = 0o


NEED FOR ALTERNATIVE MATERIALNEED FOR ALTERNATIVE MATERIAL

• Earth proposed in contract document. Earth requirement –approx. 2.0 million cum.

• Haul distance more than 100 km.• High transportation cost• Delays expected in the completion of the

project

RECOMMENDATION OF POND ASH AS AN ALTERNATIVE MATERIAL


Soil cover (1.5 m thick)

Improved Subgrade of compacted thickness not less than 50 cm

Fly ash in compacted layers of 200 mm thickness

Temporary pond ash bund

Existing embankment

Median

2

1

Proposed berm of pond ash after completion of embankment

Granular sub-base

Min. 0.5 m

Rock or boulder filling

PROPOSED ALTERNATIVES FOR CONSTRUCTION

Alternative 1

Fly ash in compacted layers of 200 mm thickness

Soil cover (1.5 m thick)

Improved Subgrade of compacted thickness not less than 50 cm

Granular material (Cu > 10)

Temporary pond ash bund

Existing embankment

Median

2

1

Proposed berm of pond ash after completion of embankment

Granular sub-base

Min. 0.5 m


Alternative II


Alternative III

RESULTS OF STABILITY ANALYSISRESULTS OF STABILITY ANALYSIS

Condition Fill material Minimum factor of safety

Unsaturated condition

Soil 1.62

Pond ash 1.92

Saturated condition

Soil 1.36

Pond ash 1.50

ARRANGEMENT FOR DEWATERING OF ARRANGEMENT FOR DEWATERING OF STAGNANT WATERSTAGNANT WATER


CONDITION OF THE GROUND AFTER CONDITION OF THE GROUND AFTER DEWATERING AND SCARIFYINGDEWATERING AND SCARIFYING


SPREADING OF GEOTEXTILE SPREADING OF GEOTEXTILE OVER SOFT GROUNDOVER SOFT GROUND


COMPACTION OF BOTTOM ASH OVER THE GEOTEXTILE


UTILISATION OF FLY ASH IN THE WIDENING PORTION OF

EMBANKMENT (AT SHASTRI PARK, NEW DELHI)

EMBANKMENT CONSTRUCTION AT SHASTRI PARK

OVERALL STABILITY OF FLY AH EMBANKMENT WITH 2 M TOE-WALL

Parameter

Pond ash

Earth cover

Sub soil

bulk 15.6 kN/m3

20 kN/m3

18 kN/m3

c 0 15 kN/m3

0

33o 28o 30o

Properties of soil

STABILITY ANALYSIS

FLY ASH EMBANKMENT WITH TOE WALL

EMBANKMENT CONSTRUCTION AT SHASTRI PARK (CONTD.)

FILTER MEDIA BEHIND RETAINING WALL

EMBANKMENT CONSTRUCTION AT SHASTRI PARK (CONTD.)

Dredging Plant used for Transporting Sand from Yamuna

Construction of embankment using Hydraulic fill Technique

Dredging of Sand Through Pipes

Construction of embankment using Hydraulic fill Technique (Contd.)

Pumping of Dredged Sand


Drainage Pipes used for Disposal of Water


Spreading of Dredged Sand using Dozer


Embankment built using Dredged Sand


Stone Pitching on Embankment Slope


Construction of Embankment in Salt Infested Area - Runn of Kutch on

Indo-Pak Border in Gujarat

The Problem• The embankment fill consists of soil excavated within

Runn of Kutch

• High salt content (0.44-1.28%)

• Rills are formed on the slope, which shows highly erosive nature of soil

7m

1:2

1.5m

India Pakistan

RD 31.975 Pak Side

Causative Factors• Overflowing of water:• Wave action• Piping phenomenon resulting in slope failure and

subsidences.• Reduction of effective stresses

The Solution (Contd)

Fig. 2 Proposed Measures for A2 and B1 Sections

Locally Available GSB

H

CC 1:4:8

GL

450

35

300

600

2.25 H

Formation Height

150

100

150 GSB 100

380

Existing Toe Wall

Provision of Toe wall and GSB


Proposed sections in water logged areas

Fig 3 Proposed Measures for B2 and C1 Sections

GL 35150

H

CC 1:4:8

450

300

600

2.25 H

Formation Height

Existing Toe Wall

Dry stone pitching filled with gravel on Existing slope

100

150 GSB 100

380

Geotextile

Fig 4 Proposed Measures for C2 Section

CR Masonryof Variable Height

150

600Dry Stone Pitching Filled with Gravel

Formation Height

Geotextile

Original side slope

Existing Toe wall

CC 1:4:8

450

380

150

100

300

35

H

2.25 H

150 GSB 100

GL


Fig. 5 Proposed Measures for locations having height of Toe wall > 1000mm

Formation Height

Geotextile

Original side slope

35

CC 1:4:8

GL

600

150

100

400

150 GSB 100

Dry CR Masonry of

Variable Height

Dry stone pitching filled with gravel on Existing slope

H

2.25 H

600

Earthwork for Road Construction

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