Hysteretic soil water characteristics and cyclic swell–shrink paths of compacted expansive soils

Abstract

The investigation of the hydromechanical behavior of unsaturated expansive soil depends on the determination of hysteretic soil water characteristic curves (HSWCCs). This research investigates the HSWCCs of two natural expansive soils initially compacted at optimum moisture content (OMC) and maximum dry density (MDD) and then saturated to their maximum expansion state to ensure identical capillary history. Filter paper, pressure plate and chilled mirror hygrometer suction measurement techniques were utilized, and corresponding measurements of three-dimensional volume change made. The cyclic swell–shrink paths were deduced in terms of volumetric strain versus either water content or suction. The cyclic three-dimensional volumetric measurements showed a much higher amount of swelling and shrinkage than those determined from one-dimensional measurements. Hydraulic hysteresis rapidly decreased with the swell–shrink cycles as a result of macro-structural stabilization. Under the no/low confining conditions, the swell–shrink cycles generally caused a decrease of global expansion and an increase of global shrinkage. Moreover, a special phenomenon showing a reduction of global shrinkage on significant drying was discovered in the less plastic soil sample.