Study On Toppling Failure Mechanism Of Rock Slope In RuMei Hydropower Station

With the developing of human activities, many roads, railways and buildings are constructed, which inevitably bring much slope hazard. Toppling failure is just one of them. Slope toppling is one of a deformation and failure type in mountain area and it is widely distributed. There are many serious accidents in construction due to toppling. Therefore, it is necessary to study formation and failure mechanism of toppling.On both sides of river and river valley, lateral unloading happens due to river erosion. Thin layer of rock bent out without being damaged. When this deformation reaches a certain degree, toppling would happen and can be converted to collapses and landslides.In this paper, geological materials of Rumei hydropower station in Lancang River, Tibet are collected based on in-situ investigation. Engineering geological, toppling deformation mechanism and three-dimensional discrete meso-element simulation method are adopted to analyze toppling deformation mechanism in steep discontinuity in middle dam site.Main research contents:1Material collection and in-situ investigation:this include geological and site investigation materials, collection. A major part of it is to carry out accurate measurement in adits from dam sites and analyze the characteristics of rock discontinuities.2Engineering geological analysis:through the statistical analysis of faults and big cracks in dam site, it is concluded the most likely deformation type is toppling.3mechanics analysis of toppling failure:based on the statistical analysis, mechanics analysis is applied to study rock slope deformation in randomized discontinuities in this area. This provide theoretical explanation to the conclusion of toppling and foundation to further research of simulation methods.4three-dimensional discrete meso-element simulation analysis:based on the analysis in2and3,3DEC is chosen to simulate the process of crust uplifting and valley incising and analyze the effects of stress and displacement fields. At last, analyze the effects of unloading cracks on toppling slope under long-term loading.5Analysis of toppling failure mechanism of rock slope in steep randomized discontinuities: based on the analysis of results of engineering geological, toppling deformation mechanism and three-dimensional discrete meso-element simulation, the mechanism of toppling in dam site is concluded.The results indicate:1Runei hydropower station is located at the upper reaches of Lancang river. The slope on both bank of it is relative steep, for the river lands in the landform of deep canyon. Cliffs and scarps form at the parts near the river bed due to the uplifting of earth crust. Gullies develop in the slopes on both banks. All of them provide the condition of free surfaces for toppling failure.2Big cracks and small faults develop well at the middle dam site area. At the left bank of middle dam site area, there is a set of bedding slope of dip of20°to30°and a reversal incline slope of60°to80°. Judging from the above, toppling failure is most likely to happen at the middle dam site.3The failure mode of rock in middle dam site is mainly bend-compound toppling failure. According to limit equilibrium analysis of typical breaking, rock block17,18, and19belong to the stable area and rock block3-16belongs to potential unstable area. Rock block1,2belong to sliding area.4Stepped excavation is applied to simulate the process of crust uplifting and cutting valley. From the first step of excavation, there is small amount of displacement at the top of slope to the outside and the displacement at the toe is the biggest. As further excavation going, displacement at the top increases and the displacement at the toe develops downwards. When it is the third step, two deformation increasing area are formed. With the proceeding of excavation, stress gradually gets released. The area at the toe bulge outward and the area at the top get lower.5Strength reduction is used for simulating long-term loading. When the parameters of rock and structure decrease by20%, the displacement at the direction of X and Y increase rapidly. A platform is formed after the cracking of the top part of the slope. Stratum bursts and a platform is formed as well as distortion appears. When it decreases by40%, toppling failure happens in the slope and it is bending toppling. The failure is in consistence with G-B method, meaning3area have been divided into, which are sliding area at the bottom, toppling area at the middle and stable area at the top. Failure happens along the weakest surface, which refers to the interface of intense weathering and middle weathering at the higher part and the crack surface in the stratum at the lower part.6The appearance of unloading cracks changes the cracking position at the slope top when toppling happens. The failure happens along the weakest structure and when they interconnected with each other, bottom boundary is decided. Due to the low mechanical parameters, the initial cracking of slope crest starts from unloading cracks. This promotes the happening of toppling failure in the slope.7Human excavations have a big effect on the toppling failure of slope. With the increase of excavation slope angle, the whole displacement of slope increases and bulges appears at some parts at the toe. The increasing of slope angel and long-term loading make toppling failure more likely to happen.