REVIEW OF LITERATURE ON EXPANSIVE CLAY SOILS.

Differential heave from moisture absorption of expansive clay foundation subsoils has been the source of considerable damage to numerous man-made structures around the world. The amount of heave actually observed is dependent on many factors, particularly climatic conditions, moisture content of the soil immediately prior to placement of the structure, and amount and type of the foundation clay. The most expansive types of soil are those that contain calcium and, especially, sodium montmorillonite minerals. The primary force contributing to heave in montmorillonite clays can be expressed in terms of suction pressures identified as osmotic and matrix potentials. The absorption of moisture by osmosis is not completely understood, but its mechanism arises from ionic charges inherent in the clay particles. This mechanism is responsible for a considerable portion of the swelling. Matrix suction pressure arises from capillary or surface tension forces and occurs only in partially saturated soils. The procedure for construction on expansive foundation subsoils begins with a design study of the site to determine the characteristics of the soil. Once these are known, the soil can be stabilized to minimize foundation heave or, if this proves impractical, the structure can be designed to withstand the expected heave. Author