Use of Problematic Soils as Engineered Fill for

Embankments

BySiva Theivendrampillai

SivakumarPrincipal Engineer (Geotechnical)

Geotechnical Branch

The problematic soils considered are:

• Expansive Soils

• Dispersive Soils

• Erodible Soils

• Problematic Soils - Normally “unsuitable materials”.

• Significant quantities of excavated materials are problematic soils. eg. High Plastic Clays

• It is very difficult to source good quality materials locally for some projects

• Cost-effective to use some or all excavated materials with constraints

WHY

Expansive ClayHigh Plasticity Clays - Potential to change in volume with a change in moisture.– Swelling upon wetting

– Shrinkage upon drying

Some indicative values for highly reactive/expansive soils:• Shrink-Swell Index > 3%• CBR Swell > 4-5% (Standard compaction, 4 days soaked)

• WPI > 3200 • LS > 12%

• Potential (eg. CH clay)• Placement (eg. Compaction Condition)• Environment (eg. Arid/Wet) - Atmospheric

Edge Effects

ShoulderSealed Surface

SeasonalVariations

for UncoverdArea

Stable Long TermConditions BeneathCentre of Pavement

DynamicMoistureBalance

Edge Effects on Pavement due to Moisture Balance

0

1

2

3

4

5

6

7

8

0 1000 2000 3000 4000 5000 6000 7000Weighted Plasticity Index (WPI)

Shrin

k-Sw

ell I

ndex

WPI Vs Shrink-Swell IndexData from:Dalby-Miles (Yarralla Dev)Dalby-Miles (Macalister)Mt Isa-Camooweal (Barkly Hwy)Cramsie-Muttaburra (Longreach)Toowoomba-Dalby (Lagoon Creek)Toowoomba-Dalby (Doctor’s Creek)

Gregory Hwy (Emerald)Goomeri-Gayndah (Burnett Hwy)Mackay-BucasiaCunningham Hwy (FG5417)Yandina-Cooroy (Bruce Hwy)Linkfield (Brisbane - R3380)

r2=0.57

Expansive Embankment Materials

LongitudinalCracks

CunninghamHighway

Average Properties:PI = 41%LS = 17%WPI = 3660Iss = 3.3

Effect of Embankment Batter Slope on Pavement Cracking

3m

3m

AssumedActive Zone3m Horizontal

Batter Slope1V:1.5H

Batter Slope1V:4H

Expansive Soil

Expansive Soil

Expansive ClaysIn Queensland

Keith Wallace (1988)

Moisture Rich >500mm/yrMoisture Hungry <500mm/yr

Dispersive SoilsClay content has a high percentage of sodium. Therefore the clay fraction readily breaks down to form a suspension in water.Indicative value for dispersive soils:

Emerson Class Number ≤ 3

Exchangeable Sodium Percentage (ESP) > 2%

A Test for Dispersive Soils

Dispersive Embankment

Materials

Warrego Highway Marburg

Cunningham Hwy Aratula

Piping or Tunnelling

DispersiveSoil

Augustine HeightsNear Springfield

Erodible SoilsLack of cohesion to resist flow of water.

Silty/Sandy soilsPI < 7 and/or

fines < 15 % (that is, % passing 0.075mm)

Rate of erosion depends on several factors such as:– Soil Properties (eg. Porosity and permeability)– Rainfall intensity– Batter slope– Vegetation

* Material that is inferior to Class D is unsuitable material

-≤ 503200 < 4000Class D*

--2200 < 3200Class C

--1200 < 2200Class B

15 – 30≥ 7< 1200Class A

% passing 0.075 mm AS Sieve

PI (%)WPIMaterial Description

Embankment Material PropertiesAs per MRTS04 (MRS11.04)

WPI = PI x % passing 0.425 mm sieve

Embankment Zones

1 to 2 m

PavementSubgrade

Upper ZoneOuter Zone

CORE ZONE

2.5m

In generalCore Zone: Expansive Clays (Class C/D), Dispersive/Erodible SoilsUpper and Outer Zones: Better Materials (Class A/B)For details: Refer MRTS04 (MRS 11.04)

Embankment Height >10m should be geotechnically designed.

Min

1.0 m when Class C and 1.5 m when Class D in

core

High

0.6 m when Class C and 1.0 m when Class D in

core

Low toMedium

Between 1V:2H and

1V:2.5H

A, B

0.6 m when Class C and 1.0 m when Class D in

core

High

A, BA, B

A, B, C

A, B, C, D

1.0Low toMedium

1V:2.5H(or

shallow)Greater

than1.5 m and less

than or equal to

6m

Outer Upper Core

General Fill ClassUpper Zone Thickness

(m)

Homogeneous

Cross-Section

Zoned Cross-SectionRainfall

Zone Batter Slope H (m)

Embankment Height between 1.5m and 6m (from MRTS 04)

Y

PavementSubgrade

Min 2.5m

5 m

Class A/B Class A/B

Class A/B

Class A, B, C, D

To be geotechnically designed>10

ROCK FILLLow to High

1V:1.5H(or

shallow)≤ 10

AAA, BHigh

A, BA, BA, B

A, B, C, D

1.5 m when Class C

and 2.0 m when

Class D in core

Low toMedium

1V:2H(or

shallow)

Greater than6 mAnd≤10 m

Outer Upper Core

General Fill Class Upper Zone Thickness

(m)

Homogeneous

Cross-Section

Zoned Cross-Section

Rainfall Zone

Batter SlopeH (m)

Embankment Height greater than 6m(from MRTS 04)

* These limits apply to material without added water. Where water is added to achieve compaction, the limits shall be 85 – 110.

60 – 8060 – 8060 – 8050 – 80< 500Low

80 – 10080 – 10060 – 9050 – 80500 – 800

Medium

100 – 140*100 – 140*60 – 9050 – 80> 800

High

Class DClass CClass BClass A

General Fill MaterialPercentage of optimum moisture content (standard

compaction)Median Annual

Rainfall (mm)

Rainfall Zone

Moisture Content Range forEmbankment Fill Materials

FromMRTS 04

Compaction Requirements(MRTS 04)

95% minimumClass C or D

(Low and medium rainfall zones)

90% minimum96% maximum

Class C or D(High rainfall zone)

95% minimumClass A or B

Road embankment

Characteristic Value of Relative

CompactionMaterialLocation

Stabilisation

Alternative to “Zoned Embankment”, stabilisation of the problematic soils can be considered. For example:• Expansive soil – Lime / cement / fly ash

• Dispersive soil – Gypsum / Lime

However it may not be cost-effective.

• Regional soil behaviour should be taken onto account

• Investigation to be carried out to identify problematic soils

• Problematic soils such as– Expansive soils– Dispersive soils– Erodible soils

can be encapsulated by better quality fill materials as per MRTS04 (MRS 11.04) for road embankment.

• Embankment Height >10m should be geotechnicallydesigned.

Summary

THANK YOU

AcknowledgmentAll staff within Geotechnical Branch