When it is raining the main reasons of the soil failure are thought to be the increase of soil weight ingenerated by rainfall infiltration, the decrease in shear strength, and the increase in infiltration by the rise of ground water. Today the evacuation signal systems are developed in case of danger and the signals are announced according to the rainfall index. These systems are useful though still have weaknesses in accuracy. By understanding the rainfall intensity, infiltration, and deformation characteristic of the foothold would contribute to the improvement of this system. In this paper, model test has been conducted using weathered granitic soil, to measure the negative pore water pressure, deformation, and ground water level. Using these three measurements the consideration on the mechanism of the slopes instable process has been done. Also the consideration on the application properties of the results of the model test has been done, using the data achieved from the in-site measurement. As a result, behavior of unsaturated seepage around the basic layer is important to calculate the surface failure and to assume the escape limit during rainfall.
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