Abstract
Either component or stress field classifies mass movement into creep and failure. If materials are soil, it will mean the shape of grain, its size distribution and its structure. Stress field consists of pore water pressure and grain-to-grain stress. It is about 10 years since R. J. Chandler, A. W. Skempton and S. Iwanaga presented their notable studies. It is their common results that landslide or landslip character depends on the clay content of moving mass. The threshold is between 20 and 30 percent. Under deformation, clay bears rarely variation in volume, while sand and silt keep dilatancy. Speciality of sand and silt is almost the same each other. The writer tried to show soil behavior by a grain model. That is, ball grain of sand and silt, and layer-built one of clay dominate their movement pattern.
