| Investigations and studies on historical earthquake damage show that the underground structures will still suffer serious damage under the action of a strong earthquakes.During earthquake,the tunnel is subjected to serious shear deformation and damage due to discontinuity of stratum,cracks in lining,water gushing caused by joint failure and other disasters which threaten the safety of the structure.In this paper,based on wave numerical simulation as the main line,the seismic response analysis and seismic isolation technology of tunnel in fault-fracture zone are systematically studied by combining theoretical analysis with numerical simulation,and the following research results are obtained:（1）Based on the wave function expansion method,the analytical solutions of the lining dynamic response levels for the "rock-liner" and "rock-isolation-lining" structural models of circular tunnels under plane SH wave incidence are derived,and the effectiveness of installing a seismic isolation layer outside the tunnel is qualitatively analysed in different rock classes.The effects of the modulus of elasticity and thickness of the seismic isolation layer on the seismic isolation effect are discussed.The results show that the seismic isolation layer outside the tunnel is effective in reducing the dynamic stress concentration coefficient of the lining,but the effect is poor in Class V surrounding rocks;the modulus of elasticity and thickness of the isolation layer affect the seismic isolation effect,the more significant the seismic isolation effect is when the modulus of elasticity of the isolation layer is 10 MPa in Class III surrounding rocks and Class IV surrounding rocks,and the minimum seismic isolation coefficient can reach 0.2;the seismic isolation effect is good when the thickness of the isolation layer is 0.3 m,and the seismic isolation coefficient can reach 0.2 in Class III surrounding rocks and Class IV surrounding rocks.The theoretical analysis was verified by finite element numerical simulation,and the numerical simulation results were consistent with the theoretical analysis results.（2）Abaqus,a finite element numerical analysis software,is used to conduct three-dimensional numerical simulation analysis to verify the effectiveness of the isolation layer outside the tunnel under Class III,IV and V surrounding rocks respectively,and to explore the influence of the modulus of elasticity and thickness of the seismic isolation layer on the seismic isolation effect.According to the result,the effect of seismic isolation layer in hard rock field is more significant than that in soft soil field,and this measure can significantly reduce the stress,strain and acceleration of tunnel lining.With the decrease of elastic modulus and the increase of thickness of isolation layer,the effect of isolation increases significantly,which match the trend of theoretical analysis.（3）Based on geological catastrophe,finite element calculation and simulation method are used to carry out three-dimensional dynamic response numerical analysis,and study the seismic response law of tunnels under the action of rare earthquakes and the working principle of isolation layer.The results show that the stress concentration of concrete lining near the circumferential joint is serious when the tunnel passes through the abrupt geological section,and the tunnel joint at the abrupt geological section is seriously damaged.The seismic damage of the tunnel can be effectively reduced by setting seismic isolation layer outside the tunnel: the peak stress and strain of the lining decreases,the stress concentration is relieved,and the circumferential joints of the tunnel are in the elastic stage.（4）Three-dimensional dynamic response analysis was carried out by using finite element calculation and simulation method to study the seismic response law and isolation technology of tunnels crossing fault fracture zone under the action of rare earthquakes.The results show that stress concentration occurs in the tunnel lining within the fault fracture zone,and the circumferential joint of the tunnel is in the ultimate failure state.The seismic damage of tunnel can be effectively reduced by setting seismic isolation layer outside the tunnel and setting seismic isolation layer between the primary lining and the lining segment.Both seismic isolation measures can reduce the stress and strain of the lining and the circumferential joints of the tunnel are in the elastic stage.This paper provides potential guidance for seismic response of tunnel crossing geological mutation and tunnel isolation design.From the Angle of tunnel isolation,the seismic damage of tunnel in bad geological section can be reduced,and provided effective seismic mitigation measures for a large number of tunnel infrastructure projects that have to cross bad geological sections in China. |
