Three-dimensional stability evaluation of a preexisting landslide with multiple sliding directions by the strength-reduction technique

Landslide 1 is located on the right bank of the downstream side of the dam for Hongjiadu Hydropower Station in Guizhou Province, China. In view of its close proximity to important workings, the stability of the slide is of great concern. Ground investigation showed that the slide is potentially unstable and has two sliding directions. Reinforcement mainly by piles was proposed as the stabilization measure, but two key questions were raised during the design of the piles. (1) How could the stability of the slope be evaluated, as there are two major sliding directions? (2) How could the shear strength parameters of the slip band be determined, as it contains a significant proportion of coarse particles? In this paper, we demonstrate how these issues can be addressed by the strength-reduction technique. First, the strength parameters of the slip band are back-analyzed by assuming a factor of safety of unity. Second, the major sliding directions are determined by carrying out finite difference analyses. Third...