Experimental research on a slope unstabilization process with a complex movement of groundwater

In Japan, many slope disasters occur by typhoon, long-term rainfall and short-time heavy rainfall, where properties and lives have been annually lost. Slope failure is still the main one of the natural disasters. Slope failure mechanism is not understood well, for example, it unable to predict the timing of failure. Therefore, a method with extensometers were applied for prediction of slope collapse (Fukuzono, 1985). However, the accurate prediction is very difficult because the allowable time for warning is sometimes too short. The warning system must be improved for the specific each slope. New rational index to predict slope failure with early stage also must be studied through such experiments. Slope failure(shallow landslide) occurs on the weathered layer with a thickness of about 1 to 2m. In such conditions, ease of infiltration by heavy rainfall makes land collapsing quite often and repeatedly. Mechanism of slope failure is induced by 1) water pressure or table by rainfall, 2) reduction of strength like cohesion, 3)increase of self weight by water. This must be verified. So we conducted the large-scale model slope test with rainfall to understand the process of slope unstabilization by large-scale rainfall simulator at National research Institute for earth science and disaster prevention. We will express the part of the results to discuss the mechanism of slope failure. In one of the main results, complex movement of groundwater in the slope play the main roll of slope unstabilization.