A series of laboratory slope failure experiments was conducted to elucidate the initiation of rainfall-induced slope failures from moisture content measurement records. The change in moisture content during the infiltration of rainwater and at initiation of slope failures was monitored by moisture sensors (Amplitude Domain Reflectrometry type). Prior to experiments, numerical unsteady seepage analyses were also conducted to identify the hydraulic response of the soil slope models to rainfall. The experiment results showed that slope failures were initiated by the increase in moisture content of the soil at the toe of the slope. Moisture content of the soil was noted to reach its saturated value at the time of failure. This indicates that rainfall-induced slope failure is a consequence of instability of the toe of the slope induced by saturation process under drained condition, and the major portion of the sliding mass may still be in an unsaturated condition. The experiments reported in this Paper also indicated that the direct measurements of change in moisture content could provide a great possibility in predicting the critical time of the initiation of rainfallinduced slope failures. Therefore, the results of applying any moisture sensors to predict and to monitor slope movements are encouraging.
Rainfall-induced slope failure is one of the most destructive natural hazards, which can occur in a matter of seconds, and without warning during a prolonged heavy rain. Most slope failures always take place annually in Japan during the rainy season in the month of June when the rainfall intensity can reach up to 100 mm/hr. The disasters have claimed untold numbers of human lives and million dollars in infrastructure losses every year in many parts of the world. In Indonesia, for example, during the last eight years, there have been about 537 lives lost due to slope failures.
