Abstract:Due to the drawback of three-dimensional strength reduction method for quantitatively determining the critical slip surface,a new method for searching critical slip surface of three-dimensional slope was presented.When the deformation of soil exceeds the critical value,shear failure could be considered to occur. Based on the displacement field obtained by three-dimensional strength reduction method,the critical displacement contour surface (interface between slip mass and stable mass) was defined as critical slip surface.The position of the shear outlet of slip mass was obtained by maximum point of shear strain increment on the boundary of specific section.Thus,the corresponding critical displacement value could be solved.FISH program was used to get coordinates and corresponding displacement value of nodes from displacement contour lines.Then the critical slip surface could be determined by discrete point data gridding. Extensive examples which contain homogeneous slope,slope imposed on loading, slope with weak layer and convex slope,were given for demonstrating the validity of the present method.The result showed that the shape of three-dimensional slope is not spherical surface,ellipsoid or logspiral surface, even for homogeneous slope.Furthermore, the application showed that there lies practicability advantage in three-dimensional strength reduction method. The assumption about the location and shape of 3D slip surface isn’t required which can truly reflect the failure mechanism of three-dimensional slope.