Analysis Of Seepage Field Of Underground Cavern Group Considering Heterogeneity Of Permeability Coefficient

With the continuous upgrading of China's energy structure and the continuous development of social economy,it is necessary to carry out a series of underground projects to relieve the stress of surface life and improve energy efficiency.The underground cavern groups of pumped storage power stations in water conservancy projects have the characteristics of large scale,large num ber,complicated drainage structure,and large span of caverns.They also have complex geological conditions and problems of seepage and seepage stability.The value of the permeability coefficient determines the calculation result of the seepage field,which is the main parameter of the calculation and analysis of the seepage,and the permeability coefficient is heterogeneous.Therefore,accurately characterizing the spatial distribution of the permeability coefficient is essential to obtain reliable numerical simulation results.The seepage field of the underground caverns during the excavation process is unstable,and the seepage field affects the stability of the excavation project.Therefore,grasping the distribution characteristics of the seepage field during the construction period plays a positive role in ensuring the construction quality of the project.The main research results of this article are as follows:(1)A heterogeneous seepage model considering the inhomogeneous distribution of permeability coefficients is established.Based on the borehole pressurized water test data,the permeability coefficient is used as a regionalized variable,and the Kriging method is used to estimate the permeability coefficient of the formation in the study area,so as to obtain the spatial distribution of the permeability coefficient of the entire area as the actual permeability coefficient of the engineering area field.In order to quickly and accurately map the permeability coefficient values to the formation model units one by one,the VOIDRI subprogram interfaced with the ABAQUS software was compiled using FORTRAN language,and then the heterogeneous seepage model was established.The homogeneous seepage field and the heterogeneous seepage field are compared and analyzed.According to the calculation results of seepage,the distribution characteristics of the seepage field and the seepage flow of the two are very different.Therefore,it is inaccurate to approximate the heterogeneous permeability coefficient field to the homogeneous permeability coefficient field for seepage calculation.(2)A method to inverse the head value of seepage boundary is proposed.In order to accurately and effectively determine the hydrogeological boundary conditions of the engineering area,and to provide a basis for the calculation and subsequent analysis of the seepage in the engineering area,a three-dimensional finite element inversion calculation model is established With the model boundary as the inversion parameter and monitoring data of the long term observation drill holes as the target function,inversion method of combining RVM and CS algorithm is used to perform inversion analysis of initial seepage field.Using RVM as an substitution model instead of finite element for calculation greatly reduces the number of finite element analysis calculations,and the fitting precision is higher.The inversion results show that,compared with the actual observation data,the calculation results of the water heads of the long term observation drill holes have an average absolute error of 7.92m and an average relative error of 1.56%.The error is small,and the change of groundwater level is consistent with the fluctuation of the terrain(3)The influence of homogeneous and heterogeneous seepage models on the calculation results of unsteady seepage in the construction period of underground caverns is analyzed,and the excavation sequence of underground powerhouse and drainage systems is compared and studied.Two kinds of layered homogeneous and heterogeneous permeability coefficient distribution schemes are designed and respectively imported into the excavation dynamic model of underground cavern group for calculation.The results show that the surface profile of the ground water,pressure head,seepage flow value and variation law of the homogeneous seepage model and the heterogeneous seepage model show large differences due to different permeability coefficients.The heterogeneous seepage model largely overestimates the time-consuming of groundwater decline,and it also has a greater misjudgment on the seepage flow of the underground powerhouse.Subsequently,the order of excavation between the drainage system and the underground powerhouse was adjusted so that the underground powerhouse was excavated before the drainage system.The delayed excavation of the drainage system slowed down the rate of groundwater discharge.At the same time,the total head line value at the same location has increased,the seepage flow of the underground powerhouse has increased significantly,and the seepage flow of the drainage system has decreased significantly.The above analysis can provide optimization ideas for the layout of seepage control measure and drainage systems,and provide a reference for obtaining a more reasonable engineering construction plan.