Observational Study of Landslide Mechanism in the Area of Crystalline Schist (Part 2) --An Application of 2-D F.E.M.--

Abstract

In order to explain the behavior of landsliding observed in an area of crystalline schist in September 1980, numerical simulation has been conducted by the finite element method under the effects of self-weight and five different pore-water pressures; corresponding to 0.25, 0.5, 0.75, 1.0 or 1.25 times the observed groundwater level. The finite element method is supplemented by joint elements as introduced by Goodman. The joint elements are so devised to express the shear stress to follow the Mohr-Coulomb's failure criterion and the normal stress not to be transmitted across a joint once the joint element has been opened by the tensile stress. The joint elements are arranged along the slip surface determined by measurements using the pipe strain-meters and an insert type of strain meter. The soil above the slip surface is assumed to be linearly elastic. By the initial position and the progression direction of rupture, crystalline-schist landslides can be classified into 3 types. This simulation explains a case where the rupture starts at a point in the slope and progresses downwards at an average velocity of a few meters per hour. It is pointed out that the progression of the rupture has been controlled essentially by rise and fall of the pore-water pressure accompanied by rainfall during the slide.