Mechanism of drying induced rebound movements in a soil slope in Sai Kung, Hong Kong

This paper reports on a study conducted during 1992–1995 on the progressive movement of a slope in Sai Kung, Hong Kong. In spite of the fact that significant downslope movement was triggered during the rainy seasons, the field data show that remarkable rebound in the uphill direction was mobilized during dry season when the groundwater level dropped. This paper focuses on such rebound deformation which is due to the drying of the soils. To investigate the mechanism of the rebound deformation, a two-dimensional finite element model of the slope was established and a series of hydraulic and mechanical analyses were conducted. It is found that the volumetric contractive behaviour caused by the increase in suction within the unsaturated soil zones and the reduction in pore pressure in the submerged soils due to the lowering of groundwater level induced the rebound deformation. Moreover, the water retention properties of the unsaturated soil zones can also strongly influence such deformation.