An Early Warning System of Unstable Slopes by Multi-point MEMS Tilting Sensors and Water Contents

A low-cost and simple method of monitoring rainfall-induced landslides is proposed that compared to a traditional instrumentation of inclinometers and extensometer, with the intention of developing an early-warning system. Surface tilt angles of a slope are monitored using this method, which incorporates a micro electro mechanical systems (MEMS) tilt sensor and a volumetric water content sensor. In several case studies, including a slope failure test conducted on a natural slope using artificial heavy rainfall, the system detected distinct tilt behavior in the slope in pre-failure stages. Based on these behaviors and a conservative approach, it is proposed that a precaution for slope failure be issued at a tilting rate of 0.01°/h, and warning of slope failure issued at a rate of 0.1°/h. The development of this system can occur at a significantly reduced cost (approximately one-third) compared with current and comparable monitoring methods. Given the cost reduction, slopes can be monitored at many points, resulting in detailed observation of slope behaviors, but the potentially large number of monitoring points for each slope does induce a financial restriction. Therefore, the selection of sensor positions needs to be carefully considered for an effective early warning system.