Research On Dynamic Response Of Underground Chamber Based On DEM-FEM Coupling Algorithm

The large hydropower projects built in the southwest of our country are mostly in the earthquake-prone areas,where the geological structures of the region are often very complex.The unfavorable geological structures,such as joints,faults and interlayer dislocation belts are developed.Under the action of earthquake and dynamic force,unfavorable geology is easily destroyed,which leads to engineering accidents of underground facilities and other hydropower facilities.Therefore,it is of great engineering significance and theoretical value to study unfavorable geology for engineering safety in earthquake dynamic response characteristics.In this paper,the DEM-FEM coupling method is applied to study the seismic response characteristics of unfavorable geology,and research on the coupling algorithm and program implementation.Based on the open source finite element software OpenSees(C++)of University of California at Berkeley and the open source DEM(FORTRAN77)program shared by Cundall and Strack networks,the interaction mode and program realization method of the coupling unit in DEM-FEM are proposed by studying the DEM-FEM coupling algorithm and the mathematical expression of its implementation.And the correctness of the coupling algorithm and the reliability of the program are verified through an example of classical wave propagation.The main work of this paper is as follows.(1)The treatment of the boundary conditions.Based on the viscoelastic artificial boundary theory and input transformation method of dynamic load on the artificial boundary,the viscoelastic artificial boundary element(VSB2D)is realized on the basis of the element interface of OpenSees.Based on the one-dimensional bar model,the corresponding viscoelastic artificial boundary and dynamic load are calculated,which proves that the viscoelastic artificial boundary element can simulate the dynamic boundary correctly.And it is verified that the dynamic load transformation at the viscoelastic boundary element can also simulate the dynamic boundary correctly.(2)DEM program encapsulation.Based on the open source DEM program,through the mixed programming technology of C++and Fortran,it is encapsulated as lib library file into OpenSees for main program call.Based on the numerical calculation model of excitation experiment,it is verified that after encapsulation,the DEM program can be called by the main program and can be calculated correctly.(3)DEM-FEM coupling calculation method implementation and coupling calculation program verification.By studying the DEM-FEM coupling calculation method,based on the OpenSees quadrilateral element,adding the calculation function in the DEM program library and modifying the unit load calculation function,the transfer of the coupling interface force is realized,and then the coupling calculation method of the DEM-FEM is realized.Based on the one-dimensional coupling calculation model,the different k_n of discrete element is selected as the calculation parameter,the transmission coefficient is the correct solution,the reasonable k_n value is given,and the dynamic calculation of different forms of load is used to verify the correctness and reliability of the DEM-FEM coupling calculation method and the calculation program.(4)Actual engineering dynamic calculation and program performance evaluation.The engineering model of underground chamber with weak interlayer is established,and the dynamic calculation is carried out.The dynamic response of surrounding rock and weak interlayer near the chamber is calculated,and the relationship between the surrounding rock and the dynamic response of the weak zone is analyzed.In addition,the performance of the simulation is evaluated according to the scale of the engineering model.