Hydro-behaviour of Middle Eastern desert soils

Surface settlement in desert areas occurs in response to fluctuating groundwater levels. Model experiments have indicated a minor settlement as a result of rise and fall of water level and this is attributed to the readjustment of soil particles to a better packing condition as a result of suction forces. Deposition of salts within the pore spaces has been found to result in swelling of 0.5–1% in medium-dense model samples, whereas dense samples showed a swelling of 4–8%. The method of drying affected the results; oven drying gave greater swelling than drying by a hot air current. The type of precipitated salt was found to control the degree of swelling; calcium sulphate results in greater swelling than that caused by calcium carbonate, and the latter exceeds that induced by sodium chloride. The results of tests indicate that changing groundwater levels can cause surface settlement and/or heave related to the associated processes of salt precipitation and/or dissolution.