ABSTRACT
Many surface failures of natural slopes or after a rain, were investigated, and laboratory rainfall experiments on model slopes were carried out. Then, the mechanism of surface failure of slope is clarified as follows: (1) Rainwater infiltrates into the soil of surface layer, and wetting front descends. (2) After wetting front reaches the base rock, groundwater table is generated and the level of groundwater table rises to some level with time. This level increases with the distance from the slope top. (3) At a point where the level of groundwater table exceeds the limit level, the surface soil of slope slides. Some governing equations for these processes are obtained, and the condition of rainfall pattern to cause surface failures is discussed.
