Shrinkage Limit of Soil (SL)
Shrinkage limit is the limiting moisture content, expressed as a percentage of the dry weight of the soil, at which a further reduction in the moisture (by evaporation) will not cause any further decrease in the volume of the soil mass but at which an increase in the moisture content will cause an increase in the volume of the soil mass. Evaporation of water causes shrinkage in a soil up to a certain degree beyond which decrease in volume does not occur ; at this stage the soil has reached its shrinkage limit. The SL represents the moisture content at the point at which the soil passes from the semi-solid to the solid state and is a means of describing the pore space present in a soil after it has been allowed to compact itself to the maximum density obtainable by shrinkage.
The SL considered in relation to the natural moisture content of soil in the field indicates whether or not further shrinkage will take place if the soil is allowed to dry out. The lower the SL of the soil, the greater is the possible volume change corresponding to a given variation in the moisture content of the soil. For friable soils, the SL may be anywhere between the LL and 50 per Cent of the LL, and for feebly plastic, 25 to 30 per cent ; for medium plastic, 20 to 25 per cent ; for highly plastic, 15 to 20 per cent. There is no definite relation between the Plastic Limit and the Shrinkage Limit.