Compressibility of Soils

Gravels, sands and silts are incompressible, i.e., if a moist mass of these materials is subjected to compression, they suffer no significant volume change. Clays are compressible, i.e., if a moist mass of clay is subjected to compression, moisture and or air may be expelled, resulting in a reduction in volume which is not immediately recovered when the compression load is withdrawn. The decrease in volume per unit increase of pressure is defined us the compressibility of soils, and a measure of the rate at which consolidation proceeds is given by the ‘‘coefficient of consolidations’’ of the soil.

Compressibility of sand and silt varies with density and, compressibility of clay varies directly with water content and inversely with cohesive strength. Clays and other highly compressible soils are known to swell when overburden pressure is removed.