DHARM698 GEOTECHNICAL ENGINEERING
Broadly speaking, soil stabilisation procedures may be brought under the following two
heads:
I. Stabilisation without additives
II. Stabilisation with additives
Stabilisation without additives may be ‘mechanical’—rearrangement of particles through
compaction or addition or removal of soil particles. It may be by ‘drainage’—drainage may be
achieved by the addition of external load, by pumping, by electro—osmosis, or by application
of a thermal gradient—heating or cooling.
Stabilisation with additives may be cement stabilisation (that is, soil cement), bitumen
stabilisation, or chemical stabilisation (with fly ash, lime, calcium or sodium chloride, sodium
silicate, dispersants, physico-chemical alteration involving ion-exchange in clay-minerals or
injection stabilisation by grouting with soil, cement or chemicals).
The appropriate method for a given situation must be chosen by the geotechincal engi-
neer based on his experience and knowledge. Comparative laboratory tests followed by limited
field tests, should be used to select the most economical method that will serve the particular
problem on hand. Field-performance data may help in solving similar problems which arise in
future.
It must be remembered, however, that soil stabilisation is not always the best solution
to a problem.
17.3 STABILISATION OF SOIL WITHOUT ADDITIVES
Some kind of treatment is given to the soil in this approach; no additives are used. The treat-
ment may involve a mechanical process like compaction and a change of gradation by addition
or removal of soil particles or processes for drainage of soil.
17.3.1Mechanical Stabilisation
‘Mechanical stabilisation’ means improving the soil properties by rearrangement of particles
and densification by compaction, or by changing the gradation through addition or removal of
soil particles.
Rearrangement of particles—compaction
The process of densification of a soil or ‘compaction’, as it is called, is the oldest and most
important method. In addition to being used alone, compaction constitutes an essential part of
a number of other methods of soil stabilisation.
The important variables involved in compaction are the moisture content, compactive
effort or energy and the type of compaction. The most desirable combination of the placement
variables depends upon the nature of the soil and the desired properties. Fine-grained soils
are more sensitive to placement conditions than coarse-grained soils.
Compaction has been shown to affect soil structure, permeability, compressibility char-
acteristics and strength of soil and stress-strain characteristics (Leonards, 1962). Soil compaction
has already been studied in some detail in Chapter 12.