Research On Stability Of Tunnel Excavation Based On Energy Dissipation Catastrophe Theory

With the continuous development of China's economy,the traffic volume has surged,and many existing tunnels have been unable to meet the traffic requirements.The expansion of existing tunnels has become an effective way to solve traffic bottlenecks.Based on the actual tunnel expansion project,this paper numerically simulates the dynamic construction process of the existing tunnel expansion into a double-arch tunnel.The stress and deformation laws of the supporting structure of the north-south excavation tunnel are analyzed,and the ground settlement law caused by the construction of the excavation tunnel is summarized.The stress and deformation of the tunnel supporting structure under different construction methods are compared,which provides a reference for optimizing the tunnel construction method.Based on the theory of energy dissipation and catastrophe,a criterion for the deformation and energy dissipation of the tunnel expansion project is established.Combined with the numerical simulation results,the safety of the tunnel expansion project is analyzed.The dynamic time history analysis of the tunnel expansion project was carried out to investigate the displacement and internal force variation of the lining structure of the excavated tunnel under seismic loading.At the same time,the corresponding rules before excavation are compared and analyzed.The influence of the excavation tunnel on the seismic performance of adjacent tunnel structures is studied,which provides reference for the seismic performance design of the excavation tunnel.The main research work and conclusions are as follows:1)The finite element analysis software MIDAS/GTS is used to establish the mechanical analysis model of tunnel excavation,and the stress and strain distribution of surrounding rock during the tunnel excavation process and the stress and deformation characteristics of the excavation tunnel support structure are analyzed.Study the variation law of surface settlement and the stress of anchor.The results show that the vertical displacement(7.5mm)of the enlarged tunnel is symmetrically distributed around the symmetrical line of the two tunnels;the surface settlement curve of the enlarged tunnel is in the shape of a single funnel and(5.5mm)W(5.7mm);the axial force(658.68kN),shear force(109.46kN)and bending moment(48.83kN·m)of the main vault,arch foot and arch waist of the enlarged tunnel;and the bolt bears the maximum axis at the excavation site during the enlargement of the tunnel.Force(28.96kN).2)Comparing the stress-strain distribution law of the one-side widening step-step arc step-by-step excavation method and CD construction method,and the variation law of ground surface settlement.Study the impact of different construction methods on tunnel expansion and excavation.Both construction methods can meet the safety requirements.Vertical displacement(7.4m m),surface subsidence(5.5mm),axial force(492.67kN),shear force(97.83kN),bending moment(15.84kN·m)and anchor axial force(20.24kN)are smaller and safer,but CD construction method is more complex,construction and demolition of temporary support is difficult and costly,so it is recommended to be long.The method of one-sided widening of the upper step arc step by step is adopted for tunnel expansion,and CD method is used for short tunnel expansion.3)Analyze the energy dissipation and mutation process during tunnel expansion.Based on the plastic dissipation energy density(PDED)and characterization of dissipation energy E_f generated during tunnel excavation construction,the energy evolution model of tunnel excavation deformation instability is established,and the energy dissipation mutation criterion of tunnel expansion instability failure is proposed.Combined with the numerical simulation results,the safety of the tunnel expansion project is analyzed.The study shows that there is no sudden change of instability in key parts of tunnel expansion project.4)The dynamic time history analysis of the tunnel expansion project is carried out to study the displacement and internal force variation of the tunnel lining structure under the earthquake load.The change law of seismic response of tunnel before and after excavation is discussed,and the influence of excavation tunnel on seismic performance of adjacent tunnel structure is analyzed.Under the action of seismic wave,the peak value of horizontal displacement of enlarged tunnel decreases with the increase of burial depth,and the greater the peak value of horizontal displacement near the ground(6.9 mm),and the tension-compression cyclic effect occurs at the 45oseismic position of the vault of enlarged tunnel structure and the internal force at the arch foot.