Seepage and stability analyses for slope susceptibility mapping within residual soils from Bukit Timah Granite in Singapore

Abstract

Climate change has resulted in a greater threat of rainfall-induced slope failures in Singapore. To identify potential slope failure sites, a slope susceptibility map can be developed. As the water table is generally very deep in Singapore, shallow slip surfaces associated with rainfall-induced slope failures often occur within unsaturated soils. Hence, a slope susceptibility map which incorporates unsaturated soil mechanics is imperative to accurately locate areas susceptible to rainfall-induced slope failures. This study aimed to develop and evaluate slope susceptibility maps for two small zonations of Bukit Timah Granitic residual soils in Singapore. Slope susceptibility maps were developed through 1D seepage analyses using Transient Rainfall Infiltration and Grid-Based Regional Slope-Stability Model (TRIGRS) and 3D slope stability analyses using Scoops3D. To evaluate results from the slope susceptibility map, 2D seepage and stability analyses were conducted using SEEP/W and SLOPE/W incorporating measured soil-water characteristic curves and soil properties from laboratory tests. Comparison between the slope susceptibility map and 2D analyses showed that factor of safety results from the slope susceptibility map were consistently lower than those of 2D analyses. Therefore, the method of using TRIGRS and Scoops3D in the development of a slope susceptibility map to predict the spatial distribution of rainfall-induced slope failure risks within small zonations was concluded to be reasonable. Slope susceptibility maps can be made easily and accessibly as TRIGRS and Scoops3D are open-source software. At areas susceptible to rainfall-induced slope failures, slope stabilisation measures such as drainage system and planting vegetation on the face of slopes can be implemented.