Soil Atmosphere Interactions for Analysing Slopes in Tropical Soils in Singapore

The modelling of soil–atmosphere interactions for slopes requires a proper understanding of the relevant soil parameters (soil water retention curve and the permeability function). This paper reports on numerical investigations of an instrumented residual soil slope in Singapore. The objective of the paper is to provide practical suggestions for choices of hydraulic parameters that can provide realistic predictions in analysing practical problems. The analyses use an uncoupled unsaturated flow model and a hydromechanical coupled model with time-dependent boundary conditions. The results obtained using measured weather data for the slope were validated against field measurements of pore-water pressure changes. The models were able to capture the trend of changes in the pore-water pressure due to rainfall events provided that account was taken of a more permeable surficial layer due to the presence of desiccation cracking and root passages. A comparative study of stability shows that the mobilised shear strength drops quickly during a rainfall event but recovers much more slowly during drying. This shows how a series of regular rainstorms with short periods of drying in between can cause a ratcheting effect, with rapid loss of strength during each period of rain that is not recovered during the intermediate drying periods.