ABSTRACT
The purpose of this paper is to make clear mechanisms of a debris flow from a soil mechanical view point. Then shear characteristics of saturated soils were investigated in use of a newly designed ring shear apparatus which can measure the pore water pressure. The accuracy of this ring shear apparatus has been made sure for the Toyoura standard sand and so on. The shear tests were done for the decomposed granite soils, Shirasu and the debris flow sediments. The results of the shear tests indicate that these soils are extremely decreased the angle of shearing resistance in terms of total stress during high-speed shearing and therefore the debris flow easily occur due to the generation of excess pore water pressure. The excess pore water pressures increase with the progression of particle crushing.
