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EXPANSIVE SOILS

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Identification

Surface Unevenness over Long Distances;

Longitudinal Cracking;

Excessive Local Deformations; Bearing Failure due to Extreme Softening

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Expansive soil showing cracks Expansive soil with "popcorn" texture

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Residential driveway damaged by reactive soils

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Typical "roller-coaster" road caused by reactive soils

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Major cracks in exterior walls at doors and windows

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Lack of appropriate void spaces under walls and slabs

No splash blocks or downspout extensions

Poor grade or reverse slope into house

Sprinkler system watering against house

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A. Walls have been properly voided using appropriate carton forms (WallVoid

System)

B. Slabs have been properly voided using appropriate carton forms (SlabVoid

System)

C. The land slopes away from the foundation. Extra soil has been added tocompensate for settlement of backfilled soils. Trash, construction debris, frozen

soil, etc., has been kept out of backfill.

D.A foundation drain has been installed - to remove any water that might reach

the basement level.

E. Shrubbery requiring low moisture is located away from the house and is hand

watered as needed.

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Field observation

Active Zone

Monsoon

d

Depth

Summer

W.C %

Monsoon

Active

zone

depth

Depth of active zone : 1.0 m to 5.5 m

Varies from place to place in the world / country

Mineral Montmorillonite / Illite

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Crack width

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Ho

H

Ho

After water is

admitted to the

soil

Before water is

admitted to the soil

Definition of Swell Pressure

Definition of Swelling PotentialH

Swelling Potential % = -------- 100

H0

H1

Ho

Load / area (p1) Load/area (ps)

Ho

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Other soil Expansive soil

Structural load Structural load

Sagging moments

Hogging moment

Base

deformation

due to structuralload

Base

deformation

due to moisture

migration

When swell pressure is

greater than structural

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MOUNT SHAPED HEAVE AND CRACKING

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Effect of Variation of Moisture Contenton Building

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APSIDC Building

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District Industries Center Building

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APSIDC Building

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Schematic of

Crackingdue to

Doming

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Cracking

due EdgeHeave

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CLAY MINEROLOGY

Basic Unit-Silica Tetrahedral

Sheet

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Basic Unit-Octahedral Sheet

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SWELLING SOILS

Identification:

1. X ray diffraction

2. Free swell test:

10 cc of dry soil (-425) 100 cc graduated jar

filled with waterFree swell (%) = (F.V I.V)*100/(I.V)

Kaolinite 80 100%

Montimorillonite - >150%Bentonite > 400% (1200 to 2000%)

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3. Differential Free Swell Test

DFS = (Soil Vol. in water Soil vol. in

kerosene)x100/(Soil vol. in kerosene)

Degree of

expansion

DFS (%)

Low < 20

Medium 20 to 35

High 35 to 50Very High > 50

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4. PI, SL and Colloidal content

PI < 15 Low

PI > 35 very high

SL > 12 Non-Critical,

10> SL > 12 - Marginal

SL < 10 critical

Colloidal content < 15% - low, > 28% - very high

Activity = PI/(% clay)

< 0.75 Low

> 1.2 Very high

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5. Swell Pressure Test

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Field conditions that favor swelling

1. Field moisture content & Equilibrium moisturecontent (Difference)

2. Fill compacted to a greater degree & OCnatural deposits swell more

3. Imposed loads are lightConsequences of swelling

Floors

Roof slabWalls pushed out wards

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Design of foundations on expansive soils

1. SBC of not more than 50 kN/m2

2. A minimum depth of foundation of 2 m

35

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35

Swelling and shrinking of soil.

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3. Bottom of trench sand or moorum or broken

stone

Side filing sand4. Plinth beams and

RCC bands to be used at foundation level

5. Under reamed pile foundation

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Soil Properties Effecting

Swell-Shrink Potential

Clay Mineralogy

Soil-Water Chemistry

Soil Suction

Plasticity

Soil Structure & Fabric

Dry Unit Weight

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Environmental Conditions Influencing

Swell-Shrink Potential 1. Initial Moisture Content

2. Moisture variations

a. Climateb. Ground water

c. Drainage & Manmade Water Resources

d. vegetation

e. Permeabilityf. Temperature

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Environmental Conditions - 2

3. Stress Conditions

a. Stress History

b. In Situ Conditions

c. Loading

d. Soil Profile

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TREATMENT

APPROACHES

Conventional Design with Appropriately

Designed Shoulders & Provision of

Drainage Measures beneath the Pavement;

Asphaltic Pavements with Special Design ofShoulders;

Rigid Pavements with Strengthened Base,

Specialised Shoulders and DrainageMeasures;

Sand-Cushioning;

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TREATMENT

APPROACHES-2

CNS Layer;

Chemical Treatment Lime;

Cement-mixed Soils;

Moisture Barriers Horizontal and Vertical;

Encapsulation; etc.

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Membrane Encapsulated

Expansive Soil

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SAND CUSHION

SAND CUSHION METHOD

MASS CONCRETE

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Sand drain all round

and at the bottom

Test Tank

150 mm Thickfly ash cushion

150 mm Thick

B.C soil bed

Dial gauge

Heave stake