Use of Problematic Soils as Engineered Fill for Embankments By Siva Theivendrampillai Sivakumar Principal Engineer (Geotechnical) Geotechnical Branch
Jun 25, 2015
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