Semi-analytical Calculation Of Plastic Stress Distribution And Relaxation Effect Of Axisymmetric Tunnel

The stress distribution of the surrounding rock is the basis of the stability analysis of the tunnel.It is not only related to the design and construction of the tunnel,but also the related to the whole tunneling engineering cost and safety.Therefore,it is important to calculate the stress distribution of the surrounding rock by using the well-defined three-dimensional yield criterion of the tunnel.The time factor is one of the important factors that affect the stress distribution of the tunnel.Stress relaxation is a concrete manifestation of stress on the time axis.Stress relaxation is an important aspect of rock rheology.However,due to the difficulty of stress relaxation experiment,there are few studies on stress relaxation phenomenon at home and abroad.At the same time,the study of rock rheology is not enough,to form a complete and mature tunnel stability control theory,still need to do a lot of basic work.In this paper,the stress distribution of three-dimensional nonlinear tunnel based on GZZ criterion is proposed,and the time factor is added on the basis of the characteristics of the sudden deformation and long-term rheological deformation of the surrounding rock.The stress relaxation behavior of the surrounding rock is established in this paper,the nonlinear stress distribution of the surrounding rock of the tunnel is calculated by collecting the predecessors' data,the theoretical analysis and the numerical calculation.The method of determining the parameters and the numerical realization are discussed.On this basis,Calculation of stress distribution under the influence of dilatancy and seepage force.And the characteristics of stress relaxation of viscoelastic-plastic surrounding rock under long-term rheological conditions are calculated.This study can provide reference for tunnel design and construction,and provide scientific guidance for engineering practice.The main work of this paper includes:1.Introduces the nonlinear failure criterion and its application in geotechnical engineering.The stress relaxation model and equation for tunnel surrounding rockare introduced.2.Based on the three-dimensional nonlinear GZZ criterion,the stress distribution of the plastic zone in the axisymmetric tunnel is deduced and the finite difference program is used to compute the higher order differential equation by MATLAB.3.The stress distribution of the tunnel is considered based on the GZZ criterion for considering the factors such as dilatancy,internal friction angle and seepage flow.4.Using the calculation results of elastic-plastic stress distribution as the initial stress field of rheology,the theoretical calculation model of the stress relaxation of the surrounding rock is established by the Nishihara model,and the Excavation Face Space Effect is considered,which is consistent with the actual tunneling force of the stress relaxation results.The influence of the parameters of the rheological model on the stress relaxation of the surrounding rock is analyzed.The theoretical calculation is compared with the numerical calculation,they had not significantly different from each other,it indicates the correctness of the theoretical calculation and can provide reference for the engineering practice.