SOIL STABILISATION (2).ppt

SOIL STABILIZATION
 Engr Ahmed Khan

SOIL STABILISATION
SOIL STABILIZATION
 The improvement process under the situation when the influence
zone is limited to less than 1m (roads etc.) is called surface
stabilization.
 Geo-Technical process of improving the engineering properties of
the soil (density, shear strength, C&O factors are improved while
compressibility, settlement and permeability reduced) and making it
more stable and durable is called ground improvement.

 Stabilizing a soil implies the modification of the properties of a soil – water – air
system in order to obtain lasting properties, which are compatible with a particular
application. The parameters involved are:
 Properties of the soil to be stabilised
 Planned improvements
 Project economies
 Construction techniques
 Maintenance of the project
 OBJECTIVES
 Reducing the volume of voids = reducing the porosity.
 Filling the voids that cannot be eliminated = reducing the permeability.
 Increasing the bonding between grains = increasing the mechanical strength.
 PROCEDURES
 Mechanical – by compaction to reduce the porosity and increase the
compressibility.
 Physical – by acting on its texture ( e.g. the controlled mixing of different grain
fractions).
 Chemical – by adding other materials or chemicals to modify its properties.

1.0 SURFACE STABILISATION
1. MECHANICAL STABILIZATION
2. PHYSICAL STABILIZATION
3. CHEMICAL STABILIZATION
4. PHYSIO CHEMICAL STABILIZATION

MECHANICAL STABILIZATION
 In this technique mechanical energy is used (rollers, plate
compactors, tampers etc. By choice or nature of soil) to
improve the soil properties by compaction.
 Preferably for construction of embankment for roads,
railways etc.
 Mechanical stability depends upon the degree of compaction.
Normally, the compaction is done at optimum water content.
Uses―
 Simplest method of soil stabilization.
 To improve the sub-grades of low bearing capacity.
 Extensively used for construction of bases, sub-bases and
surfacing of roads.

Mechanical Stabilization Cont.
Factors Affecting the Mechanical Stabilization
The mechanical stability of the mixed soil depends upon the
following factors.
(1) Mechanical Strength of the Aggregate― The mixed soil is stable
if the aggregates used have high strength. However, if the mixture
is properly designed and compacted, even the aggregates of
relatively low strength can provide good mechanical stability.
(2) Mineral Composition― the mechanical stability of the mixed soil
depends upon the composition of the minerals. The minerals
should be weather resistant.
(3) Gradation― the gradation of the mixed soil should be such that
the voids of the coarser particles are filled with finer particles to
obtain a high density.

Mechanical Stabilization Cont.
(4) Plasticity Characteristics―
―For mud roads surfacing, highly plastic soils are used as binders. They
posses greater cohesion, moisture retention capacity and provide seal
against downward movement of surface water.
―For base courses, the soils should have low plasticity to avoid
excessive accumulation of water and the resulting loss of strength.
― The soil available at site may seldom meet both the requirements. It
is necessary to mix soils from different sources to obtain desired mix.

PHYSICAL STABILISATION
 IN THIS TECHNIQUE MORE THAN TWO OR THREE SOILS ARE BLENDED TO
IMPROVE THE PHYSICAL PROPERTIES OF WEAK SOIL.
 QUITE OFTEN SOME ADDITIVES MAY ALSO BE ADDED FOR THE PURPOSE.
1. CEMENT STABILISATION
2. LIME STABILISATION
3. BITUMEN STABILISATION
4. CHEMICAL STABILISATION
5. RESIN STABILISATION

CEMENT STABILISATION
1. MOST COMMONLY USED FOR ROAD CONSTRUCTION.
2. HEAVY CLAYS ARE DIFFICULT TO PULVIRIZE AND NOT SUITABLE.
3. WELL GRADED SAND AND GRAVEL MIXTURES WITH UPTO 10% FINE BINDER
MATERIAL (PASSING#200SIEVE).
4. QUANTITY OF CEMENT TO BE DETERMINED ON TRIAL BASIS IN LAB.
(MINIMUM STRENGTH REQUIRED 3.5N/mm2—7 DAYS CUBE STRENGTH.
5. Compaction to be completed within two hours after laying mixing with water.
a. CENTRAL PLANT METHOD: Faster construction, expansive, dry mix and then
wet thoroughly, spreading and compaction.
b. MIX IN PLACE METHOD: Similar to agriculture rotary cultivator, firstly soil is
pulverized then dry cement is spread over, then water sprinkled in layers, again
remixed and shaped to camber., compacted using rollers.

Cement Stabilization Cont.
(1)Normal Soil-Cement―
• It consists of 5 to 14% of cement by volume.
• Cement is sufficient to produce a hard and durable material.
• Sufficient water be used for hydration requirement &
workability
• It is weather resistant and strong and used for stabilizing sandy and
other low plasticity soils.
(2) Plastic Soil-Cement―
It consists of 5 to 14% of cement by volume,
It has more water to have wet consistency similar to that of
plastering mortar at the time of placement.
Used for water proof lining of canals and reservoirs
Used for protection of steep slopes against water erosion.

LIME STABILIZATION
There are basically five types of lime:
 High Calcium, quick lime (CaO)
 Hydrated, high calcium lime [Ca(OH)2]
 Dolomite lime (CaO+MgO)
 Normal, hydrated dolomitic lime [Ca(OH)2+MgO]
 Pressure, hydrated dolomitic lime [Ca(OH)2+Mg(OH)2]
―The quick lime is more effective than the hydrated lime, but the latter
is more safe and convenient to handle. Generally, hydrated-lime is used.
It is also known as slaked lime.
―The higher the magnesium content of the lime, the less is the affinity
for water and the less is the heat generated during mixing.
―The amount of lime required varies between 2 to 10% of the soil.

Lime Stabilization
Lime stabilization is done by adding lime to soil. It is useful for the
stabilization of clayey soil.
―When lime reacts with soil there is exchange of cations in the
absorbed water layer and a decrease in the plasticity of the soil occurs.
―The resulting material is more friable than the original clay, and is,
therefore more suitable as sub-grade.
Types of Lime
Lime is produced by burning of lime stone in kilns. The quality of lime
obtained depends upon the parent material and the production process.

Lime Stabilization Cont.
Construction Method― Construction methods used in lime
stabilization are similar to those used in cement stabilization.
However, the following points should be carefully noted.
 The reaction in the case of lime is slow, there is no maximum time
limit between the addition of lime to the soil and the completion of
compaction.
 Lime may be added in the form of slurry instead of dry powder.
 A rest period of 1 to 4 days is generally required after spreading lime
over a heavy clay before final mixing is done.
 The soil-lime is compacted to the required maximum dry density.
 After compaction, the surface is kept moist for 7 days and then
covered with a suitable wearing coat.

Chemical & Physical Changes in Lime Stabilization
―Lime reacts with wet soil and alters the nature of absorbed layer as
calcium ions replace the sodium or hydrogen ions, the double layer is
depressed due to increase in cation concentration but sometimes
expand due to high PH value of lime.
―Lime reacts chemically with silica and alumina in soils and forms
natural cement composed of calcium-alumino-silicate.
―In Lime stabilization, liquid limit decreases, plastic limit
increases, plasticity index decreases. Soil becomes more friable
and workable. The strength of the soil is improved. Unconfined
compressive strength is increased up to 60% and the modulus of
elasticity of soil increases.
―Lime causes decrease in tendency of attraction of water.

―Soil resistance to water absorption, capillary rise and volume changes
on wetting or drying is increased.
―Lime stabilized bases and sub-bases form a water resistant barrier
which stops penetration of rain water.
―Optimum water content is increased and maximum dry unit weight is
decreased.
―In swampy areas where water content is above the optimum, it helps
in drying of the soil.

Bituminous Stabilization Cont.
―Any inorganic soil which can be mixed with asphalt is suitable for
bituminous stabilization.
―In cohesionless soils, asphalts binds the soil particles together and
serves as a binding agent.
―In cohesive soils, asphalts protects the soil by plugging its voids and
water proofing it. It helps to maintains low moisture content and to
increase in bearing capacity.
The amount of bitumen required varies between 4 to 7% by weight.

(1) Soil-bitumen (proper)― It is a water proof, cohesive soil system.
The best results are obtained if the soil satisfies the following
criteria.
 Passing No. 4 (4.76 mm) Sieve 50%
 Passing No. 40 (0.425 mm) Sieve 35-100%
 Passing No. 200 (0.074 mm) Sieve 10-50%
 Plastic Limit Less than 18%
 Liquid Limit less than 40%
 The maximum size of the particle should not be greater than one-
third the compacted thickness of the soil bitumen.
The quantity of bitumen required varies from 4 -7% of the dry weight.

Bituminous Stabilization
Certain granular soils may be stabilized by adding bitumen such as
―Bitumen Emulsion
―Cut Back Bitumen
―Asphaltic Bitumen.
The bitumen seals the pores of soil thus reducing its permeability and
may also increase the shearing strengthby providing cohesion between
the particles.

(2) Sand-bitumen―
 This is a bitumen stabilized cohesionless soil system.
 The sand should be free from vegetable matter or clay lumps.
 The sand require filler for mechanical stability.
 It should not contain more than 25% passing No. 200 sieve material
for dune sands and not more than 12% in case of other types of sand.
 The amount of bitumen required varies from 4 to 10%.
(3) Water-Proof Clay Concrete―
 Soil of good gradation is water proofed by uniform distribution of 1
to 3% of bitumen in this system.

(4) Oiled Earth―
 A soil surface consisting of silt-clay is water proofed by spraying
bitumen in two or three applications.
 Slow or medium curing bitumen or emulsion are used.
 The bitumen penetrates only a short depth into the soil.
 The bitumen required is about 5 Lit per square meter of soil surface.

Amount of Asphalt―
The quality of stabilized soil improves with the amount of asphalt up
to certain limit.
Excessive asphalt results in highly fluid mixture that cannot be
compacted.
Mixing―
The quality of the product improves with more thorough mixing.
Compaction―
The dry-unit-weight of bitumen soil depends on the amount and
type of compaction and the volatile content.
In modified AASHTO test, max. dry unit weight occurs at volatile
content of about 8%.

Construction Methods―
The following points should be noted.
 The opt. volatile content for compaction is greater than that for stability.
The requirement for thorough mixing may be even greater i.e., for clayey
soils. It is necessary to aerate the mix between mixing and compaction and
between compaction and application.
 For high stability, the layer method of construction is preferred. Each layer
is about 5 cm thick. When lower layer is dried up, subsequent layer is laid.
The total thickness for bases is between 10 to 20 cm.
 In the mix-in-place method, the bitumen is sprayed in several passes. Each
layer is partially mixed before the next pass. This method prevents the
saturation of the surface of the sub-grade.
 Climatic conditions influence the amount of bitumen applied.

Factors Affecting Bitumen Stabilization―
 Type of soil
 Amount of asphalt
 Mixing
 Compaction
Type of Soil―
It is effective in stabilizing sandy soils having little or no fines.
Cohesive soil with P.L<20% and L.L<40% can be stabilized.
Plastic clays cannot be properly treated because of mixing problems
and large quantity of asphalt is required.
Fine grained soils having high PH value and dissolved salts do not
respond well.

Chemical Stabilization
Soils are stabilized by adding different chemicals. Its main
advantage is that the setting and curing time can be controlled.
The following chemicals have been successfully used:
 Calcium Chloride
 Sodium Chloride
 Sodium Silicate
 Polymers
 Chrome Lignin
 Other chemicals

Chemical Stabilization Cont.
 It lowers the optimum water content.
 Causes a small decrease in the strength of soil.
 However if the compacted soil is put to water imbibitions, water
pick up is reduced and the strength of the soil increases.
 The benefits of the stabilization require the presence of the
chemical in the pore fluid. As the chemical is leached out, the
benefits are lost.
 Its performance depends on the ground water movement.
 The construction methods are similar to those used for lime
stabilization
 Its quantity required is about ½% of the weight of the soil.
Sodium Chloride—
 Its tendency for attraction of moisture is somewhat lesser than of
calcium chloride.

Calcium Chloride—
 It causes colloidal reaction & alters the characteristics of the soil.
 It is deliquescent and hygroscopic and reduces the loss of
moisture.
 It reduces the chances of frost heave, as the freezing point of
water is lowered.
 Effective as dust calming,
 Effective for silty and clayey soils which loose strength with an
increase in water content.
 It causes a slight increase in maximum dry unit weight.

 It forms crystallization in the pores of the soil and finally a dense
hard mat with the stabilized surface. The pores in the soil filled up
and retard further evaporation of water.
 It also checks the tendency for the formation of shrinkage cracks.
 It is mixed with the soil either by mix-in-place or by plant-mix
method and should be applied directly to the surface.
 The quantity required is about 1% of the soil weight.
Sodium Silicate—
 It is used as solution in water, known as water glass.
 It is directly injected into the soil.
 It increases the strength of the soil and makes it impervious.

 Acts as a dispersing agent.
 It increases the maximum compacted unit weight of the soil.
 The chemical required varies between 0.1 to 0.2% of the weight of
the soil.
 The method is relatively inexpensive but long-term stability is
doubtful. The treated soil may lose strength when exposed to air or
ground water.
Polymers—
 Polymers are long-chained molecules formed by polymerizing of
certain organic chemicals called monomers.
 They may be natural or synthetic.
 Resins are natural polymers and calcium acrylate is synthetic.

 When added to the soil reaction takes place.
 Sometimes catalyst is added with the monomers to the soil. In that
case polymerization occurs along with the reaction.
Chrome Lignin—
 Lignin is obtained as a by product during the manufacture of paper.
 Chrome lignin is formed from black liquor in sulphite paper
manufacture.
 Sodium bicarbonate or potassium bicarbonate is added to sulphite
liquor to form chrome lignin. It slowly polymerizes into a brown gel.
 When added to the soil, it slowly reacts to cause binding of
particles.
 The quantity required varies from 5 to 20% by weight.
 As lignin is soluble in water, its stabilizing effect is not permanent.

Other Chemicals—
 Water proofers such as alkyl chloro silanes, siliconates amines and
quaternary ammonium salts, have been used for soil water proofing.
 Coagulating chemicals such as calcium chloride and ferric chloride
have been used to increase the electrical attraction and to form
flocculated structure in order to improve the permeability of soil.
 Dispersant such as sodium hexa-metaphosphate are used to increase
the electric repulsion and to cause dispersed structure. The
compacted density of the soil is increased.
 Phosphoric acid combined with a wetting agent can be used for
cohesive soils. It reacts with clay minerals and forms an insoluble
aluminum phosphate.

2. GROUND IMPROVEMENT
ANY OF THE FOLLOWING METHOD USING ONE OR IN COMBINATION MAY
BE EMPLOYED TO IMPROVE IN SITU SOIL PROPERTIES TO SUPPORT
STRUCTURAL FOUNDATIONS;
a) DEEP COMPACTION
b) SOIL REPLACEMENT
c) PRE LOADING
d) DRAINAGE AND GWT CONTROLL
e) INJECTION GROUTING
f) SOIL FREEZING
g) USE OF GEOTEXTILES

a. DEEP COMPACTION
 DYNAMIC COMPACTION OR CONSOLIDATION;
 10-20 TONNE FREE FALING WEIGHT DROPPED FROM A HEIGHT OF 30M OR LESS. SHOCK WAVES
GENERATED TRAVELL TO CONSIDERABLE DEPTH, REARRANGING THE SOIL FORMATION TO A
DENSER AND MORE COMPACT STATE. GREATER DEPTHS UPTO 15M MAY BE TREATED USING
SPECIAL HEAVY MACHINES.
i. Low cost, rapid treatment, suitable for large variety of soils.
ii. But may harm to adjacent structures, installations, utilities, environmental issues like noise pollution.
iii. Following Control tests may be employed to monitor compaction improvement; SPT, PLT (plate), VST
(vane shear),DT (Density).
 Soil improvement depth depends on; tamper weight and its height of fall, surface area and its shape, impact
spacing and grid pattern.
 VIBROCOMPACTION
 COMPACTION PILES
 D

b. SOIL REPALCEMENT
 In this method weak/soft/organic soil is removed and
replaced with compacted engineered soil.
 This is the most reliable, economical and controlled
method, if the replaced soils are available near the site.

c. PRE-LOADING
 In this method preloading of 1.2 to 1.3 times of designed load is applied in
advance to allow desired settlement and accelerate consolidation.
 Specifically for alluvial soils having high moisture content, high compressibility
and low shearing strength by lowering water table by any means.
 Process can be accelerated by introducing sand piles in the periphery.
 Best suited for air fields, storage tanks, flood control structures etc.
 Undesired initial investment, disposal of use of preloaded soil, unexpected
time delay may be considered.

d. DRAINAGE AND GWT
 In this method ground water conditions are attained
by drains and by lowering GWT.
 Blanket drains and vertical sand drains are sometimes
employed to accelerate the consolidation process.
 Effect of lowering GWT to the adjacent structures
must be monitored and considered before applying
this method.

e. INJECTION GROUTING
 Various fluid grouts are injected in to the bore holes/weak
soils by special pressure techniques or otherwise.
 Application of this technique is mainly for reduction of
permeability, reduction of settlement, stiffening of soil,
underpinning etc.
 Grouts may be;
A. Cement grout,
B. Fly ash grout/clay grout
C. Chemical grouts

Stabilization by Grouting
In this method stabilizers are introduced by injection into the soil.
— Grouting is always done under pressure.
— High viscosity stabilizers are suitable for high permeable soils.
— Not suitable for clays because of very low permeability.
— The method is costlier than other direct blending methods.
— Suitable for buried zones of relatively limited extent i.e., pervious
stratum below a dam.
— Used to improve the soil that cannot be disturbed.
— An area closed to an existing building can be stabilized by this
method.

Depending upon the stabilizer used, grouting techniques can be
classified as under:
 Cement Grouting
 Clay Grouting
 Chemical Grouting
Cement Grouting —
 A cement grout consists of a mixture of cement and water.
 If the hole drilled in the soil is smooth, the water-cement ratio is
kept low.
 Chemicals are also added in the grout to increase its fluidity.
 Very effective for rocks with fissures, gravel and course sand.

Clay Grouting —
 The grout used is composed of a very fine grained soil and water
(bentonite clay). The bentonite clay readily absorbs water on its
surface.
 The viscosity, strength and flow characteristics of the grout can be
adjusted according to the site conditions.
 Clay grouting is suitable for stabilizing sandy soils.
 Some chemicals are also added to the clay grout.
 Clay-cement-grout is a mixture of clay, bentonite and cement.
 Clay-chemical-grout is a mixture of clay and sodium silicate.
 It is effective for medium and fine sands.

Chemical Grouting —
 The grout used consists of a solution of sodium silicate in water,
known as water glass.
 The solution contains both free sodium hydroxide and colloidal
silicic acid. An insoluble silica jell is formed.
 As the reaction is slow, calcium chloride is added to accelerate the
reaction.
 The method is suitable for medium and fine sands.
 The effect of grouting is not permanent.
Chrome-lignin Grouting —
 The grout used is made of ligno-sulphates and a haxavalent
chromium compound.
 When it is combined with an acid, ligno-sulphate is oxidized into a
gel.

f. Soil Freezing
 Soil freezing method is suitable for soils not too fine.
 This is slow, expansive and require circulation of
ammonia gas.
 Used for stabilizing excavations, for sinking mine
shafts, for recovering undisturbed soils from grannular
strata and for preventing inflow in to the excavations.

STABILIZATION BY GEOTEXTILE AND FABRICS
In geotextile stabilization, a geotextile is properly embedded in the
soil and contributes to its stability. A geotextile has high tensile
strength.
— Geotextiles are porous fabrics made of synthetic materials, such as
polyethylene, polyester, nylon, polyvinyl chloride.
— Geotextiles are manufactured as woven, non-woven or grid form.
— They are used in the construction of road over soft soils.
— Geotextile is laid over the soil and aggregate is placed directly over
it. When the traffic passes over the road, it deforms and its strength
is mobilized. The more a geotextile is deformed, the greater the load
it can carry.

Stabilization by Geotextile and
Fabrics
The soil can also be stabilized by introducing metallic strips into it
and providing an anchor or tie back to restrain a facing skin
element. The composite mixture is known as reinforced earth.

SOIL STABILISATION (2).ppt

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