| Seepage failure and landslide are the problems which often occur on embankment engineering and Earth-rock Dam engineering. Seepage analysis is the foundation for seepage safety evaluation of dam and the basis for calculation analysis of slope stability. At present, in the process of seepage calculation, it is only considered the movement condition of underground water in saturated region. In fact, water flows not only in saturated region but also in unsaturated region above the free surface. So it is necessary to use the saturated-unsaturated theory when we calculate the seepage field of embankment.Tailrace of Shawan Hydropower Station has the function of concentrating half of water head. The composition of length, design discharge and engineering cost makes the tailrace become the biggest one in China. Therefore, whether the tailrace canal bank is stability or not under the seepage action becomes the key factors to the project. In this paper, firstly, through project investigation and information collection, engineering geology and environmental condition of tailrace of Shawan Hydropower Station is evaluated. Secondly, the characteristics of seepage field about the tailrace canal bank is analyzed. Moreover, stability analysis and evaluation of canal bank is carried out. Finally, some optimized suggestions and constructive precautions are proposed. The main contents and research results of this paper are showed as follows:(1) The geologic background of Shawan Hydropower Station is analyzed, such as topography and geomorphology, formation lithology, geological structure, earthquake, meteorology, hydrogeology and so on. The engineering geological environment of tailrace canal bank on Shawan Hydropower Station has been illustrated.(2) According to geological structure, topography and geomorphology, formation lithology of tailrace canal bank passing through, geological segment of canal bank is carried out, which provides a basis for analyzing characteristics of seepage field and stability pertinently.(3) The saturated-unsaturated theory of seepage calculation is introduced. The significance of soil-water characteristic curve and permeability function is described. Moreover, the determination method is introduced. The calculation model is established by the finite element simulation software. According to parameters originated from test, the two-dimensional finite element calculation model is established. By numerical simulation calculation, the changing rule of seepage field under different conditions is analyzed. The relationship between the variation of water head, slope ratio, thickness of concrete cutoff wall, saturated permeability coefficient of concrete cutoff wall and the seepage field of tailrace canal bank is described.(4) Groundwater level of tailrace canal bank is monitored by the disposition of piezometric tube during construction. Changing rule of groundwater level before and after passing water is analyzing. Results of numerical simulation and results of monitoring are contrastively analyzed, finding that they anastomose well. The characteristics of seepage field within the canal bank are revealed by the results of numerical simulation.(5) The theory of unsaturated soil slope stability analysis is described. On the basis of calculating seepage field, stability analysis for tailrace canal bank is carried out. The stability coefficient of tailrace canal bank under different conditions is calculated and the results of calculation are evaluated. At the same time, the relationship between the variation of water head, slope ratio, saturated permeability coefficient of concrete cutoff wall and the stability of tailrace canal bank is described.(6) Some optimized suggestions of tailrace canal bank are proposed and some constructive precautions are also proposed. Research shows that the results have guiding significance and reference significance for analyzing and designing similar tailrace of hydropower station. |
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