STABILIZATION OF SOIL BY ADDING ADMIXTURES

(A) Mechanical Stabilization

(B) Chemical Stabilization

(A) Mechanical Stabilization

•Correct proportioned materials (aggregates & soil) when adequately compacted to get a mechanically stable layer, the method is called mechanical stabilization.

1. Compacted aggregates with no fines:-

No cohesion.

So stable when confined only.

Highly permeable.

No frost action.

Figure-1. Aggregates compacted without fines.

2. Compacted aggregates with compacted fines, just for filling voids:-

Stable even when unconfined.

Less permeable.

Frost action.

Figure-2. Aggregate compacted with fines.

3. Compacted aggregates with excessive fines:-Aggregate float in soil.

Poor drainage.

Easy compaction.

Less strength.

More change to frost action.

Figure-3. Aggregate compacted with excessive fines.

(B) CHEMICAL(Admixture) STABILIZATION

1. Lime Stabilization

2. Lime Flyash Stabilization

3. Cement Stabilization

4. Bitumen Stabilization

1. Soil – Lime stabilization• For silty clay and clay soil.

• For soil having PI > 10.

• Ca(OH)2 > 70 %.•

Figure-4. Effect of lime content on properties of clay soil

LIME SOIL

2-3% ALLUVIAL SOIL AND MOORUM

3-5% CLAY/BC

5-6% HIGH EXPENSIVE SOIL

2) LIME FLYASH STABILIZATION

Suitable where lime and fly ash are locally available .

For soil having medium PI(5-10) and clays that do not respond to line alone

Figure – 5. Lime flyash stabilization

3. USE OF CEMENT STABILIZATION:-

For soils which do not respond to lime

Where higher and faster development of strength is required

For water locked and high rainfall areas

For granular soils/sandy soils

Area of harmful salts and organic matter

CEMENT CONTENT

1. sands/sandy soil/ soil gravels of low P.I. 3-5%

2. silts/silty clays 4-8%

3. clay/ B.C. soil 8-15%

FACTORS INFLUENCING PROPERTIES OF SOIL CEMENT

1) Soil type – clay less strength

2) Cement content – 25-26% > strength decreases

3) Pulverisation and mixing –lumps

4) Compaction – settlement in future

5) Curing – very important

6) Additives – Calcium Chloride give better strength

A) BRITISH METHOD :-

Comprehensive strength of specimen with different cement content,

cured for 7 days

Sample 5cm diameter,

10cm height

tested after 7 days

cement content corresponding to 17.5 kg/cm sq strength is required cement % for light medium traffic

for heavy traffic road 28-35 kg/cm sq may be adopted

Figure – 6. Variation of compressive strength with cement %

B) PCA METHOD

durability of soil cement specimen to withstand the specified, wet-dry or freeze-thaw cycles

loss after 12 cycles should not exceed the following limits

MAXIMUM BRUSHING LOSS % BY WT. SOIL TYPE AS PER HRB

14 A-1, A-3, A-2-4, A-2-5

10 A-2-6, A-2-7, A-4, A-5

7 A-6, A-7

In PCA method, the design criteria are based on durability of ability of the soil cement specimens to withstand the specified wet-dry cycles.

SOIL –BITUMEN STABILIZATION

FACTORS INFLUENCING/AFFECTING PROPERTIES OF SOIL BITUMEN MIX

1) Soil type

2) Type of bituminous material

3) Amount of Bitumen

4) Mixing

5) Compaction

6) Curing

7) Additives(CaCl2, CaSo4)

(SPECIALL SUITED FOR DESERT AREAS)

Figure – 7. Variation of properties of mix with bitumen content

SPECIAL TREATMENTS IN WATER LOGGED AREAS

1. 3-5% lime

2. Sand blanket for capillary cut off is provided to check the movement of moisture. Thickness of sand blanket in cm=(8/d) where

D = (2d1+d2)/(d1+d2)= mean dia. in mm

D1 = aperture size of sieve(mm) through which the fraction passes

D2 = aperture size of sieve(mm) on which the fraction is retained

3. Primer coat or compromising of 50% high speed diesel oil and 50% bitumen is applied on the subgrade and sides of the trench @ 1kg/cm sq