Abstract
Natural slope Failure deals with many complicated factors, such as rainfall pattern, properties of soil, ground water, and seepage water.
At present, we do not have enough technique for treatment of natural slope stability. So, it is useful that we study the behaviour of natural slope failure by field observation data.
We pile up data from 201 spots where natural slope failure actually occurred from 1969 to 1971, and examine their characteristics, by extracting 18 elements, such as failure pattern, height and width of failure, and amount of rainfall. As for the failure pattern, slide of surface sail has eminent position and its avarage thickness is 2m. As for the rain fall, it is reasonable, that it reaches critical point for danger of slope failure, when contineous rainfall amounts 100mm, or 20mm for 24 hours.
