The Simulation Method And Application Of Stress-Seepage Coupling Of PD-FEM-FVM In The Engineering Rock Mass

With the rapid development of transportation infrastructure construction in China,a large number of highway and railway tunnels,water conservancy and hydropower projects will be built to the western mountainous areas and karst areas with more complex geological conditions and the seabed with more severe environment.Tunnel construction is faced with a series of engineering geological problems and the threat and test of geological disasters,which often induce a series of major engineering disasters such as instability of surrounding rock and water inrush,which seriously restrict the safety of tunnel construction.A deep understanding of the mechanism and evolution of underground engineering disasters is the theoretical basis for disaster prevention and control.Numerical simulation has become the main research method due to its scientific,economical and intuitive advantages.The key to simulating rock mass fracture problems such as instability of surrounding rock lies in the continuous-discontinuous dynamic transformation process.As one of the most advanced numerical calculation methods for solving discontinuous problems,peridynamics is especially suitable for the above problems.However,peridynamics has the problems of large amount of calculation and low computational efficiency in engineering scale simulation.In this paper,the coupled calculation of peridynamics and traditional continuum mechanics is used to solve this key problem.First of all,for the solid part,a hybrid modeling method is used to propose an PD-FEM coupling calculation method to efficiently solve the static failure problem,which improves the efficiency of peridynamics in solid calculation.Secondly,based on the above-mentioned PD-FEM coupling calculation method for the solid part,the fluid part is calculated by FVM based on Darcy’s law,and the PD-FEM-FVM fluid-structure coupling calculation method is established based on the transition layer,which further improves the fluid-structure coupling calculation efficiency.It is successfully applied to the Shantou Bay Subsea Tunnel(subsea tunnel constructed by mining method)to simulate the engineering-scale subsea tunnel excavation process under the coupling action of stress and seepage,and to reveal the influence of different influencing factors on the stability of the surrounding rock of the subsea tunnel.In general,the theoretical analysis,mathematical derivation,program development,calculation example verification and engineering application are adopted in this paper.Research is carried out around the theme of "the Simulation Method and Application of StressSeepage Coupling of PD-FEM-FVM in the Engineering Rock Mass".The main research results include:(1)In terms of solid computing,the peridynamics based on non-local interactions is more computationally intensive and less efficient than the traditional continuum theory based on local interactions,and the bond-based peridynamics is limited by Poisson’s ratio.Therefore,based on the hybrid modeling method,a calculation method based on ordinary state-based peridynamics and finite element method coupling is proposed to quickly solve the static failure problem.By forming the global matrix of the coupled system and using the adaptive dynamic relaxation method,the peridynamics and finite element method are solved under the framework,which speeds up the convergence speed and greatly improves the calculation efficiency.The accuracy and effectiveness of the coupling method for calculating the static failure problem are verified by two classical examples of bar subjected to compression and plate with a circular hole under tension.The method is successfully applied to the simulation of the excavation process of an underground cavern group,and the calculation results are consistent with previous studies.And compared with the pure PD method,the PD-FEM coupling method greatly improves the computational efficiency,which is of great significance for the realization of engineering scale simulation.At the same time,the validity and superiority of this method in predicting the excavation damage zone(EDZ)distribution characteristics and the deformation law of the surrounding rock in the underground cavern group are proved.(2)In terms of fluid-structure coupling calculation,the solid part of the current PD-FVM coupling calculation method still uses peridynamics calculation,and there is a waste of resources in solid calculation and information interaction,and the calculation efficiency can be further improved.Therefore,the PD-FEM coupling method proposed above is used to describe solid deformation and fracture,FVM is used to describe fluid seepage based on Darcy’s law,and the PD-FEM-FVM fluidstructure coupling calculation method is established based on the transition layer,which is used to efficiently simulate saturation crack propagation in porous and fractured media.The accuracy and efficiency of this method for simulating the deformation and failure of saturated porous media are verified by porous media seepage and hydraulic fracturing problems.At the same time,the influence law of stress state on hydraulic fracturing crack propagation is studied by this method,and the inducing effect of stress ratio on hydraulic fracture propagation is proved.The phenomenon of obvious deflection of the crack to the direction of the maximum principal stress(or perpendicular to the direction of the minimum principal stress)is shown,and it is concluded that the crack initiation pressure is positively correlated with the stress,which is basically consistent with the previous test and simulation results.(3)The key to the simulation of damage and failure of rock mass under the action of stressseepage coupling lies in the continuous-discontinuous dynamic change process.Engineering-scale simulation puts forward higher requirements for the establishment and solution of numerical models.Therefore,relying on the engineering background of the Shantou Bay Subsea Tunnel(subsea tunnel constructed by mining method),and using the PD-FEM-FVM fluid-structure coupling calculation method,the simulation of the engineering-scale subsea tunnel excavation process under the action of stress-seepage coupling is carried out.The simulation results are consistent with COMSOL Multiphysics simulation results are in good agreement.The validity of the method for simulating the fluid-solid coupling problem of engineering-scale rock mass is verified,and the influence law of subsea tunnel excavation on the displacement field,seepage field and damage state of surrounding rock is analyzed.At the same time,the computational efficiency of this method is 1.78 times and 4.31 times that of the pure PD method and the PD-FVM coupling method respectively,which proves the high efficiency of this method in simulating the fluid-solid coupling problem of engineering-scale rock mass.It is of great significance to promote the application of peridynamics in the field of geotechnical engineering.(4)The construction environment of subsea tunnels is complex.It is very important for tunnel construction to understand the influencing factors and laws of surrounding rock stability,and to ensure the stability of surrounding rock during tunnel construction.Therefore,the influencing factors of surrounding rock stability of subsea tunnels are summarized and analyzed:geological factors and human factors.Relying on the engineering practice of the Shantou Bay Subsea Tunnel(subsea tunnel constructed by mining method),the simulation of the engineering-scale subsea tunnel excavation process under multiple working conditions was carried out.By comparing and analyzing the distribution characteristics of the tunnel surrounding rock excavation damage zone,displacement field and seepage field under different influencing factors,it is revealed that the tunnel burial depth(ground stress conditions),seawater depth(groundwater pressure),surrounding rock elastic modulus(physical and mechanical properties)and construction method on the stability of surrounding rock of subsea tunnels.It provides a scientific basis for the prediction of the instability of the surrounding rock and the safe construction of the subsea tunnel.