The aim of this study is an estimation of expression on landslides. Writer applies thermodynamics theory as the method of analysis, because landslides are outcome of the physical phenomenon. By this way, the estimation of expression on landslids could be expressed as follow. Ca/a=f·Rr·d-1/(m+1)·(R-r)1+1/(m+1) but, Ca: landslides area a: basin area f: constantical coefficient Rr: relief ratio m: coefficient by precipitation pattern d: coefficient by precipitation pattern R: continual precipitation r: continual precipitation on innocent to landslides By using the above the estimation of expression, writer can explain the qualitative phenomena on land-slides that have been observed till now and obtain the following conclusion. (1) On the same precipitation, percentage of landslide areas is in straight proportion to relief ratio. (2) In spite of the same precipitation, the difference of percentage of landslide areas appears by respec-tive patterns of it. (3) Writer can get the relation between percentage of landslide areas and precipitation from curve of 2nd order to 1st order.
Slope failure is occured by seepage water and often begins from the partial failure. We investigated experimentally the relation between the hydraulic gradient of ground water and the partial failure at the foot of the slope. An experimental equipment has a length of 3 meters, a width of 1.5 meters and a depth of 0.3 meters. It is supported at the angle of 30 degrees. Soil was uniformly filled up in it. The rainfall was supplied on it with the intensity of 50mm/h. The ground water of four different hydraulic gradient was occured by changing drainage conditions at the lower end of the equipment. The results and comments are summarized as follows. 1) The partial failure at the foot of the slope was caused by the seeping of the ground water, and the more the ground water had the steep hydraulic gradient, the more the partial failure extend rapidly upper part. 2) It was found that the ground water affecting the partial failure at the foot of the slope could be theoretically approached by applying Dupuit-Forchheimer assumption to the inclined impermeable layer.