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Abstract The volume of Zhenggang large landslide accumulation body in Gushui hydropower station is up to 4.75×107 m3. Geological investigation shows that the landslide is mainly composed of bedrock，slip zone soil and unconsolidated accumulation，and that the slip zone soil layer is the transfixion slipping surface. Firstly，the history evolution process of the accumulation body and the formation mechanism of the landslide were analyzed in detail. Qualitative discrimination was made on the current situation and the future instability mode. The landslide is in the state of creep deformation along the transfixion slipping surface. Based on the analysis of basic characteristics of slip zone soil，the large-scale direct shear tests on slip zone soils in laboratory were carried out under different conditions. Not only the relations of deformation and strength and the values of shear parameters in natural state were studied respectively，but also the effects of stone and water content on shear strength were analyzed. The reasonable calculation parameters were found，and the stability analysis was conducted. The analysis results show that the values of cohesion and internal friction angle range from 30.31 to 43.94 kPa and 25.82°to 30.49°，respectively. The contents of stone and water have significant influences on shear strength. The threshold value for stone content is 75%，increasing the stone content which is less than 75% causes the increase of shear strength；However，the shear strength decreases when stone content is higher than 75%. The shear strength and values of parameters decrease with the increasing water content，with which the relations are approximate to exponential function. The stability results are consistent with the qualitative analysis，and the landslide is possibly slumped under any condition. Therefore，it is very important to choose the best economic and reasonable treatment and evaluation.
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Received: 25 November 2011
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2013, Vol. 32 
