Journal of Natural Disaster Science

PREDICTION OF PROBABLE SURFACE FAILURE USING 3-D SLOPE STABILITY ANALYSES AND THE SLIDING DIRECTION

Takashi OKIMURA
Associate Professor, Reclamation Engineering Research Institute, Faculty of Engineering, Kobe University, Nada Kobe 657, Japan

(Received 23 March, 1994 and in revised form 8 February, 1995)

Abstract

A three-dimensional slope stability analysis method, called the three-dimensional multi-planar sliding surface method, was proposed previously (Okimura & Maeda [5]; Okimura & Morimoto [6]). It gives the site and volume of the critical sliding mass, as defined by the minimum safety factor. The method for shaping an assumed sliding mass that is nonrectangular in plan has been defined by taking into account the equilibrium of the forces between columns within an assumed sliding mass (Okimura [7]). In these studies, the sliding direction of the assumed sliding mass was set parallel to the steepest direction of the most unstable cell that had been found as proposed previousiy (Okimura & Ichikawa [4]). The sliding direction of the assumed sliding mass, however, may change according to the shape of the assumed mass. A method for calculating the sliding direction is proposed that is based on the equilibrium of the forces being at a right angle to the sliding direction. It was applied to an actual mountain slope on which shallow failures caused by heavy rainfall had taken place. The sliding direction calculated by this method was nearly the same as that of the actual failed mass. Using the obtained sliding direction, the coordinates of a digital land elevation model were transformed and slope stability analyses made by three 3-D methods: the multi-planar sliding surface method, and the 3-D Hovland and the simplified Janbu methods. Results showed that the most critical sliding masses obtained using the calculated sliding direction were closer to the actual sliding masses than those obtained using the most unstable cell's sliding direction.

Key words

prediction of mountain slope failure, shallow failure, three-dimensional slope stability analysis, probable sliding direction, digital elevation model