Feasibility study on dam and reservoir construction in the catchment area of complex karst water system: Taking Pucha Reservoir of Beipan River as an example

The topographic and geological conditions in the basin of Beipan River are complex with high mountains and deep valleys on both banks, strong karst development and deeply buried groundwater.Consequently, water resources are in great shortage in this area. The construction of water conservancy projects can effectively solve the problem of water shortage. However, karst leakage has become a difficult problem restricting the construction. By comprehensively using the methods of geological survey and mapping, drilling and geophysical exploration, hydrogeological test, karst water system analysis and groundwater balance analysis, this paper demonstrates that a leakage to the adjacent valley or along the karst pipeline deep under the dam foundation will not occur in the Pucha reservoir, but the possibility of solution crack leakage is great. The finite element method is used to simulate the solution crack leakage and analyze the engineering impact. Results show that with the increase of the dissolution rate of T₁yn^1-1 limestone, the anti-sliding stability coefficient of the dam foundation decreases slightly, and there is an inverse correlation between them. The regression equation is y₁=−0.081x +2.678. The potential instability mode of the dam foundation is that the T₁yn^1-2 marl rock mass is sheared at the upstream, and the bottom is sheared along the gently inclined upstream with weak structural plane of rock debris mixed with mud in T₁yn^1-2 layer. With the increase of dissolution rate of T₁yn^1-1 limestone, the leakage of dam foundation increases significantly, and there is a positive correlation between them. The regression equation is y₂=120.3x+224.8. The concentrated belt of solution crack is the main leakage area of dam foundation. When the concentrated belt develops horizontally and distributes intensively along the contact belt between T₁yn^1-1 limestone and T₁yn^1-2 marl, the anti-sliding stability coefficient of dam foundation will significantly reduce and the leakage of dam foundation will significantly increase.Therefore, the concentrated belt should be treated as a key area. When the concentrated belt is vertically developed, dispersed or mainly distributed in the area behind the dam, it has little impact on the anti-sliding stability and leakage of the dam foundation, and can be used as a secondary treatment area. Karst hydrogeological analysis and numerical simulation show that in complex karst areas, after groundwater is discharged from the surface in the potential catchment area, it mainly influxes in the form of runoff to the downstream river channel, and the vertical infiltration of water flow is relatively weak, so it is difficult to form karst pipelines bypassing the anti-seepage curtain and connecting the upstream and downstream in the deep part of the riverbed. The leakage form of dam foundation is mainly solution crack leakage, and its engineering impact is limited. Therefore, the catchment area of karst groundwater is suitable for dam and reservoir construction. In addition, according to the spatial distribution characteristics of the concentrated belt of solution crack, the targeted treatment of zoning grouting can improve the treatment efficiency and save investment.