Influences of “underground erosion” on instability of a crystalline schist slope

As the cause of instability of slopes, 1) Change of slope profile (toe erosion, artificial excavation, etc.) 2) Increase of pore pressure are generally known. However, according to our field investigation and measurement of a crystalline schist landslide, instability of the slope can not be explained by 1)change of slope profile or 2)increase of pore pressure, but we have found “underground erosion” must be the main cause of instability of the slope. “Underground erosion” has hardly been studied in engineering field and geological or geomorphological field up to now. However, “underground erosion” is the main cause of instability of some crystalline schist slopes and it acts a vital role in landslides triggered by vertical subsidence ( Sassa et al. 1980a , b )