Destabilizing Mechanism Analysis And Stability Evaluation Of A Large Accumulation Bank Slope At An Alpine Gorge Reservoir

The construction of Xiaowan Hydropower Station made the water level rise to 1240m step by step, also may bring about an enormous impact on environment to the two banks of Lancang River and Yangbi River.The changes in environment, especially in hydrogeology condition, caused the leading edge of slope collapse or deformation of the integrity and instability, and would also bring about potential problems to peo-ple's lives and property living in reservoir and to the safety of the dam.Several typical banks was discussed in this paper.The basic technological route sequence was described as follows,site research-analysis of factors-conceptual model-analysis of deformation and damage-stability assessment.Through the engi-neering geological conditions,rock and soil structure and mechanical properties of the slope, the analysis of factors affecting slope,the deformation mechanism and failure mode of slopes was studied in-depth,the water impact on the banks as well as the slope stability was mainly discussed,and then analysed the slope stability affected by the rate of the water level changing. Next step computing software FLAC-3D was used to further simulate the natural state and the state after reservior water uplift of the slope,then the result would be used to analyse the slope stability.Main content and and research results are as follows:(1)Combining the investigation of the reservior bank slope, the rock structure and physical characteristics of mechanical properties.At the work of water,physical characteristics of mechanical properties would be decline.(2)Through a series of trials in and out room,we could get a series physical and mechanical parameters of accumulation body,such as natural severe,cohesive force ,permeability coefficient and so on,which could be refered for permeability co-efficient.(3)For the water level and the vertical speed of the influences of seepage field, taken Wuzhi Bank as an example. During water impounding, the change of ground-water seepage field could be roughly divided into the following three steps: the stage of strong recharging groundwater from reservoir water, the stage that deep groundwa-ter saturation line of slope uplift and the phase of form a stable groundwater seepage field. As the impounding velocity increased, the bending level of the instantaneous groundwater saturation line significantly increased. The dew point of instantaneous groundwater saturation line in the slope was generally higher than the water level elevation. When water level descended, as the rate of decline increased, this elevation gradually increased.(4)The natural state, after water storage and rainy day state of the bank slope were simulated analysis with FLAC-3D. Follow-up from Wuzhi Bank terms of the changes, the simulation results and reality could be a good fit. The numerical re-sults showed that water storage as well as rainstorm conditions, the front of slope was likely to occur locally Instability and Failure, this had been verified in practice.(5)Through the analysis of several typical slopes stability, we could see the way accumulation body instability was also the more or less of its submerged parts of the relevant and slope type. When the accumulation of small parts of the body submerged in the water as well as a Steep front, the reservoir water might im-pact the role of performance was not very clear, mainly for the front of the digerosion caused by the collapse of local instability, such as the Wuzhi Bank; On the contrary, in the accumulation of large parts of the body submerged in water, it was likely to lead to overall instability of large accumulation of body damage, such as reservoir section of Huangtian Landslide.