PREDICTION OF THE SHAPE OF A SHALLOW FAILURE ON A MOUNTAIN SLOPE - THE 3-DIMENSIONAL MULTI-PLANAR SLIDING SURFACE METHOD

A three-dimensional multi-planar sliding surface method developed from the two-dimensional method is proposed to identify the shape and/or v olume of a shallow failure that appears on a mountain slope during hea vy rainfall. The method is constructed to satisfy the equilibrium of f orces in the cross-sectional and longitudinal directions on an assumed sliding mass that is regarded as being rectangular in plan shape. It was applied to a digital elevation model to determine the site and for m of a critical sliding mass on a mountain slope. Calculations made wi th a testing model of a simple planar slope show that the safety facto r calculated using this method is similar to factors obtained by the 3 D Hovland and 3D simplified Janbu methods. The method was applied to a n actual mountain slope on which a shallow failure caused by heavy rai nfall took place. The most probable unstable mass calculated by the mo del was almost the same as that at the failed site. The method propose d can be used to predict a potentially unstable mass that leads to sha llow failure.