Numerical Study On Stability Of Surrounding Rock Of The Expressway Tunnel Based On General Particle Dynamics

Taking the Expressway Tunnel as an example,this paper carries out C++ programming,self-programming of stability of surrounding rock during tunnel excavation and comparative analysis of stress field,displacement field and plastic zone by mature software abaqus,and analysis of influence of joints on displacement and plastic zone of intact rock.Underground tunnel excavation is to form a new space structure under the original stress state of rock.The excavation process will cause the destruction of the original strata structure and the initial stress state,and the surrounding rock will form a new equilibrium state.The formation process is stress redistribution.Stress redistribution causes the deformation of surrounding rock.If the deformation of surrounding rock is too large,it will easily cause engineering accidents and economic losses.A meshless method is to describe the state of a system by using a series of discrete points.Each particle has its own independent field variables,such as mass,momentum and coordinates.Two conservative equations of GPD method are discretized by density approximation method.The acceleration formula is obtained by discretizing the momentum conservation equation.In order to prevent the non-physical oscillation of the results in the solution domain,the linear artificial viscosity should be added to make the solution more smooth and eliminate the numerical oscillation.Geotechnical engineering deformation is a problem of low-speed movement compared with collision and impact.In order to prevent non-physical penetration of particles,especially when particles approach or almost collide.So the final acceleration consists of three parts:(1)discretization of momentum conservation equation.(2)Linear artificial viscosity.(3)Physical viscosity part.The continuity density approximation equation can be obtained by using particle approximation method for mass equation,but it is more convenient and fast to use the medium density summation method in practice.However,when particles are located on the boundary of the problem domain,the density summation will lead to the edge effect,that is,the associated density will be neglected.The relevant solution obtained by reading the literature is to eliminate the edge effect by constructing virtual particles.Another difficulty of density summation is to calculate the smoothness function between particles before completing its own density solution.However,density summation reflects the essence of GPD approximation method,so density summation method is adopted.The most widely used B-spline function is chosen to construct smoothing function,which is proposed by Monaghan and Lattanzio on the basis of cubic spline function and is similar to Gauss function.The boundary effect mentioned above is easy to be truncated by the boundary when integrating,and the integral region can not be the whole model,which is not in conformity with the actual situation.The particles on the boundary are only affected by the particles in the boundary,and there is no influence on the particles outside the boundary,so the calculation results will have errors.The virtual particle is introduced into the boundary,and its position coordinates are symmetrical with the outermost layer of real particles.The density and pressure in the field variables of the virtual particle of type are the same as that of the real particle of the symmetrical point,but the velocity of the virtual particle of type is opposite.But the virtual particle of type is not enough to prevent the real particle from penetrating the boundary,so the virtual particle of type is introduced.When the virtual particle of type is adjacent to the real particle,it will be at the center line of the two particles.A force is created to prevent particles from penetrating the boundary.The ideal elastic-plastic constitutive model and D-P yield criterion are adopted for rock.The time integral is frogjump method,and the stress state of each ion is interpolated in half time step.The above analysis process basically includes the content of C++ program calculation module.The main research contents include:The program can be roughly divided into three parts:(1)model input.(2)Particle pairing.(3)The calculation of field variables.Particle pairing is mainly accomplished: local sensitive hashing principle is used to reduce the size of particle pairing search and save time.At the same time,it completes many pairing tasks to solve the problem that the calculation of kernel function does not conform to the actual situation,and then affects the calculation of field variables.The calculation of field variables is mainly accomplished by using multi-threading parallel technology,which greatly improves the efficiency of program operation and the scale of operation.(2)The simulation of the Express Channel Tunnel verifies the rationality of the selection of chamber spacing and cross-section form of the Express Channel Tunnel so as to avoid the penetration of the plastic zone.(3)Comparing the stress field,displacement field and plastic field with the finite element software Abaqus,and comparing the simulation results with the mature commercial software Abaqus,the reliability and applicability of GPD meshless method are verified.(4)Based on the validation of the meshless GPD method,the displacement field and plastic zone of rock with non-penetrating joints are compared and analyzed,and the hot issues of geotechnical engineering are further explored.The main innovations of this paper are as follows:(1)Complete particle search pairing optimization,shorten pairing time,achieve multiple pairing;use multi-threading technology,field variables calculation speed is accelerated,solve the programming difficulties of large deformation problems and calculation inaccuracy defects.(2)The applicability and reliability of GPD method and C++ self-programming are verified by comparing and analyzing the results of deformation field,displacement field,plastic zone GPD method and finite element method of surrounding rock in the excavation of the Expressway Tunnel.(3)Contrastive analysis of displacement field and plastic zone of intact and nonpenetrating jointed rocks and preliminary exploration of possible causes...