Geotechnical Engineering

DHARM

SOIL STABILISATION 705

Applications

Soil-cement is used as base course for pavements for light traffic. Pressed soil-cement blocks

can be used in place of bricks. Rammed earth walls with just 2% cement are used for low-cost

housing. Soil-cement blocks may be used in place of concrete blocks for pitching of banks of

canals or canal linings.

17.4.3Bitumen Stabilisation

Bituminous materials such as asphalts and tars have been used for soil stabilisation. This

method is better suited to granular soils and dry climates.

‘Bitumens’ are nonaqueous system of hydrocarbons which are completely soluble in

‘Carbon disulphide’.

‘Asphalts’ are natural materials or refined petroleum products, which are bitumens.

‘Tars’ are bituminous condensates produced by the destructive distillation of organic

materials such as coal, oil, lignite and wood. (Lambe, 1962).

Most bitumen stabilisation has been with asphalt. Asphalt is usually too viscous to be

incorporated directly with soil. Hence, it is either heated or emulsified or cut back with a

solvent like gasoline, to make it adequately fluid.

Tars are not emulsified but are heated or cut back prior to application.

Soil-asphalt is used mostly for base courses of roads with light traffic.

Bitumen stabilises soil by one or both of two mechanisms: (i) binding soil particles to-

gether, and (ii) making the soil water-proof and thus protecting it from the deleterious effects

of water.

Obviously, the first mechanism occurs in cohesionless soils, and the second in cohesive

soils, which are sensitive to water. Asphalt coats the surfaces of soil particles and protects

them from water. If also plugs the voids in the soil, inhibiting a flow of pore water.

Bitumen stabilisation maay produce one of the following:

(i) Sand-bitumen

(ii) Soil-bitumen

(iii) Water-proof mechanical stabilisation

(iv) Oiled earth

Sand-bitumen

Cohesionless soils like sand stabilised by bitumen are called sand-bitumen. The primary func-
tion of bitumen is to bind the sand grains. The quantity of asphalt may range from 5 to 12%.

Soil-bitumen

Cohesive soil stabilised by bitumen is referred to as soil-bitumen; the primary objective is to
make it water-proof and preserve its cohesive strength.

For best results the soil must conform to the following requirements:

Max. size : less than one-third the compacted thickness

Passing 4.75 mm sieve : greater than 50%

Passing 425–μ Sieve : 35 to 100%