Abstract
In the Higashi-Kishu area of Mie prefecture, many slope failures occurred by the typhoon No.12 which attacked 2011. As a result of examining the situation of landslides, based on the aerial photographs, geological maps, and DEM, about 90% of 290 landslides had occurred in the Kumano acidic rock area.
Many landslides were concentrated on slopes directed from southwest to southeast. The gradient of slopes concentrated 30 to 40 degrees with the Kumano acidic rock south block, 35 to 45 degrees with the Kumano acidic rock north block. And, the slope forms before failures consisted of valley-type slopes (47%), straight slopes (48%), and ridge-type slopes (5%). As a result of field work, landslides had occurred at grade DL (strongly weathered saprolite) and/or grade DM (moderately weathered granitoid) or the boundary of a grade DH (decomposed granitoid) and talus sediment. In the collapsed places, sheeting joints were confirmed and inclination to valley side at part of columnar joints were confirmed. It was guessed that landslides generated at the remarkable part of deformation by gravity. Along joints exists grade DH. The coefficients of permeability of grade DH were about from 10−5 to 10−6 m/s. And, the electrical conductivities of springs were as low as from 3 to 4 mS/m. It was thought that shallow groundwater at rain was participating in landslides.
