Rainfall-induced shallow landslides are major hazards affecting the natural environment in steep forested terrain. Typically, these landslides occur in initially unsaturated residual soils overlying the bedrock. The failure mechanism involves a decrease in soil shear strength associated with the reduction in matric suction as a result of soil wetting followed by the development of positive pore water pressure at the sliding surface due to rain-water infiltration. Hence, a key issue in the assessment of rainfall-induced shallow slope instability is the correct evaluation of pore water pressure variations within the unsaturated soil deposit during rainfall. This project focuses on changes in pore water pressure and wetting front development during rainfall by employing a series of field, laboratory and numerical investigations to accurately evaluate the transient response of an unsaturated residual soil slope subject to rainfall infiltration. Field-monitored variations in matric suction during various rainstorm events together with information on soil hydraulic properties provided by laboratory tests performed on residual soil samples from the study site are used to establish and calibrate the hydraulic parameters of a finite-element model for transient seepage analysis that is used to investigate infiltration patterns within the analysed residual soil domain.

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