Precaution and early warning of surface failure of slopes using tilt sensors

A simple monitoring method for the early warning of rainfall-induced landslides is proposed. Tilting angles in the surface layer of the slope are mainly monitored in this method. In the first stage of this study with a scaled model slope, distinct behaviors were observed in the tilt angles monitored on the surface of the slope prior to failure. Hence, a set of equipment has been developed for practical use, which is equipped with a Micro Electro Mechanical Systems (MEMS) tilt sensor and a volumetric water content sensor. An optional arrangement of tilt sensors has also been developed in order to investigate the deformation of the deeper layers. These sets of equipment have been deployed at several slope sites in Japan and China, and their performances have been recorded. Slope failure tests were also conducted on a natural slope by applying artificial heavy rainfall. The developed system detected distinct behaviors in the tilting angles at these sites in the pre-failure stages. Considering the behaviors of tilting monitored on the surfaces of these slopes, it is proposed that a precaution be issued at a tilting rate of 0.01° per hour and a warning be issued at a tilting rate of 0.1° per hour, to be on the conservative side.