This presentation is about various approaches adopted for stabilizing soil using natural and chemical admixtures.

1. SOIL
STABILISATION
Prepared by:
Arbaz M. Kazi
B.E, M.E (Civil Engg.)

2. • Soil Stabilisation in a wide sense incorporates different
methods utilized for altering the properties of soil to enhance
its physical properties and engineering performance.
• Soil Stabilisation is, no doubt utilized for a range of
engineering tasks, the most well - known application being in
the road construction and airfield pavements, where the
primary goal is to build the soil quality or stability and to
lessen the development cost by making best utilization of
locally accessible materials.
DEFINITION:

3.  It is a well known fact that, every structure must rest upon soil or be
made of soil. It would be ideal to find a soil at a particular site to be
satisfactory for the intended use as it exists in nature, but unfortunately,
such a thing is of rare occurrence.
 The alternatives available to a geotechnical engineer, when an
unsatisfactory soil is met with, are
(i) to bypass the bad soil (e.g., use of piles),
(ii) to remove bad soil and replace with good one (e.g., removal of peat at
a site and replacement with selected material),
(iii) redesign the structure (e.g., floating foundation on a compressible
layer), and
(iv) to treat the soil to improve its properties.
When Stabilisation is done:

4. Advantages of Stabilisation:
1. To improve the strength of sub-bases, bases and sometimes surface
courses, in case of low cost roads
2. To bring about economy in the cost of road.
3. To make use of inferior quality of locally available soils/material. (
every time it is not possible to find required or specified strength in
locally available material at that time we can go for soil Stabilisation
methods)*
4. To improve certain undesirable properties of soils, such as excessive
swelling or shrinkage, high plasticity, difficulty in compacting etc.
5. To facilitate compaction and increase load-bearing capacity
6. To reduce compressibility and thereby settlements.
7. To improve permeability characteristics.

5. Methods of Stabilisation
Stabilisation without additives
1.1. Mechanical Stabilisation
2.2. Stabilisation by drainage
Stabilisation with additives
1. Stabilisation using lime
2. Stabilisation using cement
3. Stabilisation using Bitumen
4. Stabilisation using Calcium
chloride or Sodium chloride

6. STABILISATION
WITHOUT USING
ADDITIVES

7. MECHANICAL SOIL STABILISATION
 Mechanical stabilization is a process of mixing two or more soils to
with different particle size gradations to produce a new soil with
desired engineering characteristics
 Then the mixture is compacted to the required density using
conventional method
 The soil may be mixed at the construction site, at a central plant, or
at a borrow area
 Adequate mixing and compaction are required for successful
mechanical stabilization
 This technique may be used in preparing the subgrades, faces and
surfaces

8. TYPES OF MECHANICAL
STABILIZATION
1. Soil-aggregate mixture.
2. Sand-clay mixture.
3. Sand-gravel mixture.
4. Stabilization of soil with soft aggregate.

9. SOIL-AGGREGATE MIXTURE.
 Soil-aggregate is a material in which soil and aggregate
particles are mixed in suitable proportion such that the
resulting mixture conforms to a dense and stable mix when
properly compacted.
 This technique is used in countries abroad for the construction
of base courses, and in the case of low traffic roads for the
surface course as well.

10. SAND-CLAY MIXTURE.
 The sand-clay road is composed of a favourable mixture of
clay, silt and sand. This blending can alter the undesirable
properties of clay significantly.
 This mixture give good result only if proper equipment's are
used and quality control is done.
 When used as sub-base mix should have a minimum soaked
CBR of 20, When used as base for heavily traffic road mix
should have a minimum soaked CBR of 80

11. SAND-GRAVEL MIXTURE.
 In tropical countries, the materials obtained from the disintegration of
laterite are extensively found in a natural admixture of clay and
coarse fractions and is known as lateritic gravel.
 In India, this material is locally known as Moorum. Often the natural
Moorum contains to much of plastic material which lower its value as
road pavement material.
 A suitable admixture of Moorum with sand will not only result in a
better gradation and increased strength but also will reduce the
plasticity.
 Sand Moorum mixture find ready application in sub-base and bases in
India.

12. STABILIZATION OF SOIL WITH SOFT AGGREGATES
 A method of stabilization of soil using soft aggregates is known
as Mehra’s method the principle behind this method is to embed
in a soil mortar, coarse aggregates roughly one-third of the total
volume.
 The aggregates are normally soft aggregates such as over-burnt
brick ballast, kankar, Moorum or laterite. Because of the larger
proportion of the soil mortar, the resulting material has no grain
to grain contact in the coarse aggregates, which merely float in
the soil.

13.  Each aggregate is thus enveloped all round in the compacted
soil and is thus protected from the crushing effect of traffic.
 This enables the soft aggregate to retain its strength and
angular character for an indefinite period.
 About 10 percent of the coarse aggregates which are collected
are not mixed with the soil but are saved and spread on the
layer of the soil aggregate mixture before rolling. the soil-
aggregates mixture is compacted to maximum dry density at
optimum moisture content.
STABILIZATION OF SOIL WITH SOFT AGGREGATES

14. STABILISATION BY DRAINAGE
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.
The strength of a saturated soil depends directly on the
effective or intergranular stress.
For a given total stress, an increase in pore water pressure
results in a decrease of effective stress and consequent
decrease in strength.

15. Thus, drainage of a soil is likely to result in an increase in
strength which is one of the primary objectives of soil
stabilisation.
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, using well-
points, sand-drains, etc.,
3. application of an electrical gradient or electro-osmosis; and,
4. application of a thermal gradient.
STABILISATION BY DRAINAGE

16. STABILISATION
USING
ADDITIVES

17. When lime is added to a fine-grained soil, a number of reactions take
place. Some of them occur immediately while others are slow to
occur. One of the early reactions is base-exchange. Clay particles are
usually negatively charged with exchangeable ions of sodium,
magnesium, potassium or hydrogen adsorbed on the surface.
The strong positively charged ions of calcium present in lime replace
the weaker ions of sodium, magnesium, potassium or hydrogen
resulting in a preponderance of positively charged calcium ions on the
surface of the clay particles. This in turn reduces the plasticity of the
soil.
SOIL-LIME STABILIZATION

18. The clay particles tends to agglomerate into large sized particles
(flocculation), imparting friability to the mixture.
After above first reaction are complete, any additional quantity of
lime will react chemically with the clay minerals. The aluminous
and siliceous materials in the clayey soil will react with the lime in
presence of water to form cementitious gels, which increase the
strength and durability of the mixture.
This pozzolanic reaction are slow and extend over a long period of
time, several years in some instance another possible source of
strength is the formation of calcium carbonate due to the absorption
of carbon dioxide from air.
SOIL-LIME STABILIZATION

19.  Cement is a standard material whose quality is tested and assured.
Because of its very high flexural strength, it has a vary high load
spreading property. Thus soil-cement is able to spread the load
over a wider area and bridge over locally weak spots of the
underlying sub-grade or sub-base.
 The main disadvantages are
1. The cost being higher than lime-soil
2. The need of high degree of quality control
3. If volumetric change take place when cement hydrates it results
in early shrinkage cracks
SOIL-CEMENT STABILIZATION

20.  Calcium chloride has deliquescent and hygroscopic properties.
 By the former is meant the ability of material to absorb
moisture from the air and become liquid, the latter is meant the
ability of material to absorb and retain moisture without
necessarily becoming liquid. granular soils lack stability when
they are too dry.
 By adding calcium chloride their moisture content can be
stabilized and the soil can be used successfully in road
construction. We can also apply a number of other chemicals
like sodium silicate, Resins, molasses, fly ash, etc.
SOIL-CALCIUM CHLORIDE STABILIZATION

21. SOIL-SODIUM CHLORIDE STABILIZATION
The stabilising action of sodium chloride is somewhat similar
to that of calcium chloride but it has not been widely used.
It attracts and retains moisture and reduces rate of evaporation.
Another advantage is the crystallisation of the salt in the soil
pores, which retards further evaporation and also reduces
formation of shrinkage cracks.
The salt is not applied on the surface, but it is mixed into the
soil by mix-in place or plant-mix methods

22. SOIL-BITUMEN STABILISATION
 Asphalt and tar are the bituminous materials which are used
for the stabilisation of soil. These materials are normally too
viscous to be incorporated directly with soil.
 The fluidity is increased by either heating, emulsifying or by
cut-back process.
 The bituminous material when added to a soil impart
cohesion or binding action or reduced water absorption.
 Thus either by binding action or water-proofing action or
both actions may be utilised for stabilisation.
 Bitumen stabilisation can be classified as:

23. Sand-Bitumen
 It is referred as 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%.

24. Soil-bitumen
• 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 (0.075 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

25. Water-Proof mechanical stabilisation
 Soil of good gradation is water proofed by uniform distribution
of 1% to 3% of bitumen in this system.
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.