2. INTRODUCTION
Stabilisation in a board sense, incorporates the varios methods
employed for modifying the properties of a soil to improve its
engineering peformance .
Stabilisation is being used for a variety of engineering works, the
most common application being in the construction of road and
air-field pavements.
where the main objective is to increase the strength or stability
of soil and to reduce objective is to increase the strength or
stability of soil and to reduce the construction cost by making best
use of the locally available materials.
3. CLASSIFICATION OF THE METHODS OF
STABILISATION
1.Stabilisation additives without.
2.Stabilisation with additives
Classifications may be based on the treatment given to
soil, on additives used, or on the process involved.
Broadly speaking, soil stabilization procedures may be
brought under the following two heads
4. Stabilisation with out additives may be “mechanical” re-
arrangement of particles through compaction or addition
or removal of soil particles.
. It may be “drainage”- drainage may be achieved by the
addition of external load
Stabilisation with additives may be cement stabilization
(that is soil cement), Bitumen stabilization, or chemical
stabilization
5. STABILISATION OF SOIL WITH
OUT ADDITIVES
Some kind of treatment is given to the soil in this
approach; no additives are used.
The treatment may involve a mechanical process like
compaction and a change of gradation by addition or
removal of soil particles
6. MECHANICAL STABILISATION
Mechanical stabilisation involves two operations
1. changing the composition of soil by addition or
removal of certain constituents, and
2. densification or compaction. The particle size
distribution and composition are the important factors
governing the engineering behavior of a soil.
Significant changes in the properties can be made by
addition or removal of suitable soil fraction for
mechanical stabilisation .
7. Where the primary purpose is to have a soil resistant to
deformation and displacements under loads soil
materials can be divided into two fractions
The granular fraction retained on a 75 micron IS Sieve
and the fine soil fraction passing a 75 micron sieve.
Mechanical stabilization has been largely used in the
construction of cheap roads.
Typical examples are given in Table 31.1.
8. Table 31.1 Typical Gradation Specifications
of Mechanically.
Is Sieve
Percentage passing
Base Surfacing Base or surfacing
Max. Size Max. Size Max. Size
40 mm 20mm 20mm 10 mm
40 mm 100 - - -
20 mm 80-100 100 100 -
10 mm 55-80 80-100 80-100 100
4.75 mm 40-60 50-75 60-85 80-100
2.0 mm 30-50 35-S60 45-70 50-80
1.18 mm - - 35-60 40-65
600 micron 15-35 15-30 - -
300 micron - - 20-40 20-40
9. Note:
(i) For bases: Liquid limit not exceeding 25% and
plasticity indes not exceeding 6.
(ii) For surfacing: Liquid limit not exceeding 35% and
plasticity index between 4 and 9.
10. STABILISATION BY DRAINAGE
Generally speaking, the strength of a soil generally
decreases with an increase in pore water and in the pore
water pressure.
Addition of water to a clay causes a reduction of
cohesion by increasing the electric repulsion between
particles
For a given total stress, an increase in pore water
pressure results in a decrease of effective stress and
consequent decrease in strength.
11. The methods used for drainage for this purpose are
1. Application of external load to the soil mass,
2. Drainage of pore water by gravity and/or pumping
4. Application of a thermal gradient.
using well points, sand – drains, etc
3. Application of an electrical gradient or electro
-osmosis; and,
12. STABILISATION OF SOIL WITH ADDITIVES
The mode and degree of alternation necessary depend
on the nature of the soil and its deficiencies.
If additional strength is required in the case of
cohesionless soil, a cementing or a binding agent may
be added and if the soil is cohesive, the strength can be
in creased by making it moisture – resistant, altering the
absorbed water films, increasing cohesion with a cement
agent and adding internal friction.
Swelling and shrinkage may also be reduced by
cementing, altering the water adsorbing capacity of the
clay mineral and by making it moisture – resistatnt.
13. BITUMEN STABILISATION
Asphalts and tars are the bituminous materials which
are used for stabilization of soil, generally for pavement
construction.
These materials are normally too viscous to be
incorporated directly with soil.
bitumen stablisation is classified under the following four
types:
(i) Sand bitumen
(ii) soil –bitumen
(iii) water – proofed mechanical stablisation and
(iv) oiled earth.
14. CHEMICAL STABLISATION
Calcium chloride
Sodium chloride
Sodium silicate.
Calcium chloride is used as a water retentive additive in
mechanical stabilized bases and surfacing
The stabilising action of sodium chloride is somewhat
similar to that of calcium chloride, but it has not been so
widely used
The sodium silicate solution in water, known as water
glass, in combination with other chemicals, such as
calcium chloride, is used as an injection for stabilizing
deep deposits of soil.
15. CEMENT STABILISATION
Portland cement is one of the most widely used
additives for soil stabilization.
Factors affecting the soil-cement
Nature of the soil
Cement content
Compaction
Mixing
Admixtures
Designing and testing soil – cement
Field construction of soil-cement
