地すべりにおけるすべり面の起源

Abstract

Many landslides occur in stratified rock mass; a few landslide, in massive rock mass. In order to explain the phenomena, the joint system in the two geological area is examined on the basis of permeability (Lugeon value) and boring core observation. This reveals that deeper joints are more widely spaced and joints extend much deeper in the stratified rock mass. It is considered, therefore, that the joints are formed under stress relief field and develop remarkably in the stratified rock mass with different elasticity layers.A prerequisite for the occurence of a landslide is the existence of a permeable discontinuous fracture dipping toward a valley. Landslides in stratified rock mass move in general, along the stress relief joints. Even in massive rock mass, many landslides occur in peculiar geology, in which remarkable swelling is founded during tunnel excavation. Consequently, slip surfaces of landslides are regarded to originate mostly in joints, due to expansion of either stratified or massive rock mass.