Seepage Analysis And Evaluation Of Seepage Control Effect In The Right Bank Of Baihetan Hydropower Station

Due to the influence of topography,stratum lithology and geological tectonic evolution,the hydrological and geological conditions of the right bank of Baihetan hydropower station are extremely complex.After impoundment of the reservoir,groundwater level near it will be significantly uplifted,and the characteristics of groundwater movemen will change significantly.In order to evaluate the reliability of the anti-seepage and drainage system of the right bank of Baihetan hydropower station,this paper builds a large three-dimensional finite element model,which reflects geological characteristics,layout of the project and seepage control system,based on detailed analysis of the hydrogeological conditions in the right bank of Baihetan.The seepage field characteristics and seepage control effect of the right bank after impoundment are analyzed and evaluated by using seepage analysis method,which combines submodel,variational inequality and self-adaptive penalty function(SVA).The main research work and results of this paper are as follows:(1)Based on water-pressure borehole test data and combined with weathering and unloading characteristics of rock mass of the right bank of Baihetan,The rock mass of the right bank is divided into several zones and equivalent permeability coefficient of each zone is calculated.According to the characteristics of fractures in the rock mass,the permeability tensor of each zone is determined by using fracture specimen method.The results show that the permeability of rock mass in the right bank of Baihetan can be divided into six zones:strong permeable zone,upper part of medium permeable zone,lower part of medium permeable zone,upper part of weak permeable zone,lower part of weak permeable zone and almost impermeable zone,medium permeable zone is mainly distributed in shallow surface and near the tectonic structure plane.The permeability of tectonic structure plane exhibits strong anisotropy,and the permeability which parallel to tectonic structure plane is significantly higher than that of perpendicular.(2)Based on the permeable zones and corresponding permeability coefficient,the hydrological and boundary conditions of the right bank of Baihetan is analyzed by using inverse analysis method,which is combined neural network with genetic algorithm.The results of inverse analysis show that groundwater level on the right boundary of model is between 825 and 890m,and the variation of groundwater level is consistent with that of terrain.The average error between calculated and measured borehole water level is 6.4m,it shows that the inverse result is reasonable and reliable;it also indicates that the permeability of rock mass and its spatial variation are accurately expressed.(3)A three-dimensional finite element model of the right bank of Baihetan is bulided,which reflects geological characteristics,layout of the project and seepage control system.By using seepage analysis method which combines submodel,variational inequality and self-adaptive penalty function(SVA),the seepage characteristics and seepage control effect of the right bank of Baihetan after impoundment are evaluated.Analysis results show that the effect of drainage system is significant;the anti-seepage system can effectively cut off main leakage path composed of F16 F18 C3-1 C4 C5 as well as other strong permeable structural planes.Furthermore it also indicates that the anti-seepage and drainage system can significantly reduce groundwater level and osmotic pressure of rock mass in the right bank of Baihetan.