Rainfall-induced slope failure occurs in many parts of the world especially in the tropics. Many rainfall-induced slope failures have been attributed to antecedent rainfalls.Although, it has been identified as a cause of rainfall-induced slope failure, the pattern or distribution of the antecedent rainfall has not received adequate attention. In this study, parametric studies were performed using three typical rainfall patterns identified by analysis of available rainfall data of Singapore and two different soil types to represent high and low conductivity residual soils of Singapore. Antecedent rainfall patterns were applied on soil slopes and a transient seepage analysis was conducted. The computed pore-water pressures were used in stability analyses to calculate factor of safety of the slope. Results indicated that antecedent rainfall affected stability of both high conductivity (HC) and low conductivity (LC) soil slopes. However, it affected the stability of LC soil slope more significantly than HC soil slope. Patterns of antecedent rainfall controlled the rate of decrease in factor of safety, the time corresponding to F s(min) and the value of F s(min) . Delayed rainfall pattern resulted in the lowest minimum factor of safety, F s(min) , for HC soil slope and advanced rainfall pattern resulted in the lowest F s(min) for LC soil slope.

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The unsaturated permeability function is often estimated from the soil-water characteristic curve (SWCC) of a soil. A complete SWCC measurement can improve the estimation of the unsaturated permeability function. In most laboratories, the SWCC can be measured up to a suction of 100 kPa using a Tempe cell. However, complete measurement of the SWCC is an expensive and time-consuming task. Therefore, this paper presents a new approach to estimate SWCC data points beyond 100 kPa suction to complement the SWCC measured up to a suction of 100 kPa. The new SWCC is then used to estimate the unsaturated permeability function. The proposed approach uses knowledge of the grain-size distribution curve and measured SWCC data at 100 kPa suction to estimate the SWCC data points beyond 100 kPa suction. To verify the proposed procedure, SWCC tests were conducted over a wide range of suctions for coarse kaolin and a triaxial permeameter system was used to directly measure unsaturated permeability of the coarse kaolin. The proposed procedure is found to reduce the variation between unsaturated permeability functions estimated by various estimation models.