Centrifuge Model Test on Unsaturated Expansive Soil Slopes with Cyclic Wetting–Drying and Inundation at the Slope Toe

Abstract

The influence of dry unit weight and matric suction on the shear strength and deformation characteristics of unsaturated expansive soil was studied by triaxial tests. Artificial rainfall system and lighting–winding system were, respectively, set up for the unsaturated expansive soil slope centrifuge models to simulate wetting–drying cycles. Three kinds of centrifuge model tests concerning different sequences between centrifuge running and wetting–drying cycles on slope surface and inundation at the slope toe were conducted on the unsaturated expansive soil slope models with two different dry unit weight, water contents and slope ratios. The slope settlement and horizontal displacement, failure mechanism, and cumulated cracks on unsaturated expansive soil slope centrifuge models were investigated and analyzed. It was found that the crack accumulation induced by wetting–drying cycles or softening behavior induced by inundation at the slope toe was crucial to understanding the rainfall-induced progressive failure, which occurred from the slope toe and developed upwards in unsaturated expansive soil slopes. Therefore, cover layer should be built for unsaturated expansive soil slopes from rainfall infiltration into the cracks induced by wetting–drying cycles, and at least enough drainage measures should be taken to reduce water infiltration into the unsaturated soil slope and inundation at the slope toe.