Effect of different rainfall and soil properties on slope stability in Singapore

Abstract

As a result of climate change, rainfall-induced slope failures have generated a significant amount of studies in recent years. In unsaturated soil mechanics, infiltration of water decreases the suction and shear strength of the soil, which could trigger slope failures. As residual soils in Singapore often exist in unsaturated condition, slope failures are of a major concern especially during rainfall events. Therefore, this project aims to investigate the stability of residual soil slopes under various rainfall conditions using residual soils with different soil-water characteristic curves (SWCCs), shear strength and permeability from Jurong Formation soil in Bukit Teresa and Old Alluvium in Tampines. Furthermore, regional 3D seepage analyses and stability analyses of unsaturated residual soil slopes were conducted in order to investigate the variations in factor of safety (FoS) with different rainfall. The conclusions drawn from this project indicated that residual soil with higher permeability experiences a quicker decrease in FoS under higher intensity maximum daily rainfall. This was observed from the analyses with Old Alluvium soil from Tampines. On the other hand, residual soil with lower permeability experiences a more drastic decrease in FoS under maximum 5-day antecedent rainfall. This was observed from the analyses with Jurong Formation soil from Bukit Teresa. Effective cohesion value and angle of friction are other aspects that affect FoS values apart from rainfall conditions as shown with the high FoS values of Old Alluvium (Tampines).