Abstract: The volume of Zhenggang large landslide accumulation body in Gushui hydropower station is up to more than 47,500,000 m3. There are many ultra-deep landslide places with the thickness over 50 m; its stability is directly related to dam construction and operation. However, Field engineering geological investigation and data of deformation caused by rainfall in 2008 show that the landslide is multi-period and complex, mainly composed of bedrock, slip soil and unconsolidated accumulation. There are so many tensile and shear cracks on the surface that the accumulation body is prone to produce creep deformation under the normal condition and slump under any condition, so the treatment such as excavation and reinforcement is needed. Due to lateral restraint of computation cross-sections and bottom sliding surface curvature effects in space not considered by two dimensional method, 3D limit equilibrium method and large deformable Lagrange finite difference method are applied to build some 3D computational model according to actual geological information. By comparative analysis of changes of stress, deformation, plastic zone and safety factor before and after the treatment, the stability is evaluated qualitatively and quantitatively; and furthermore the stability after the reinforcement is checked by the finite element point and surface safety factor method. The results truly reflect the situations and laws of stability of the landslide, which are consistent with the field exploration results. The local and whole stability obviously increased after excavation and reinforcement; if combined with drainage measures will be more conducive to maintaining. The research results can provide meaningful references to the similar projects.

Key words: hydropower station, large-scale landslide, accumulation body, three-dimensional limit equilibrium, three-dimensional numerical simulation, stability, safety factor