Sensing and monitoring for assessment of rainfall-induced slope failures in residual soil

Real-time monitoring can be used to assess the effect of climatic conditions on slope stability. However, this can be costly. There is therefore need for a methodology to select critical slopes for stability monitoring using comprehensive field instrumentation throughout the year. In this study, the Transient rainfall infiltration and grid-based regional slope stability (TRIGRS) model was used to generate a slope susceptibility map (SSM) of Singapore. This model was selected as it can incorporate unsaturated soil properties in spatial analyses of water infiltration and factor of safety (FoS) calculations. Available studies on establishing SSMs by incorporating unsaturated soil mechanics principles are limited and most focus on mountainous areas. This paper presents relatively new research on the development of a SSM for a densely populated area like Singapore. The study area was limited to residual soil from Bukit Timah Granite in Singapore. TRIGRS helped to determine zones that are highly susceptible to failure; the instrumentation can be used to monitor high-risk areas during dry and rainy periods. A selected slope was instrumented with tensiometers, moisture sensors, piezometers and a rain gauge, all connected to a data logger for real-time monitoring. The changes in pore-water pressure and soil moisture with time during wet and dry periods were used for slope stability analyses. FoS variations over time can be used to assess slope stability, especially during periods of heavy rainfall.