Study On Structural Mechanical Behavior And Seismic Mitigation Measures Of Metro Tunnel In Loess Area Under Earthquake Action

The seismic research of tunnels is one of the important issues in the field of disaster prevention and mitigation in underground engineering.In recent years,urban subway projects have been rapidly developed,and seismic research on subway tunnels has also become extremely important.In view of the status quo of research on anti-seismic mitigation of subway tunnels in loess area,this paper firstly studies the analytic solution of the longitudinal response of subway tunnels under earthquake action based on the theory of elastic foundation beams.At the same time,taking the Jinye 2nd Road-Zhangbalu Road section of Xi’an Metro as the engineering background,a numerical model was established using ANSYS finite element software to compare the influence of different parameters on the internal force and displacement of the tunnel structure.On this basis,the influence of different damping measures on the internal force and displacement of the tunnel structure is studied.And the damping effects of different damping measures are compared and analyzed.The main research work are as follows:Based on the theory of elastic foundation beams,the analytical solution of the longitudinal response of subway tunnels under earthquake action is studied.Assuming the free field displacement of the soil under the seismic load is a sinusoidal displacement and the traveling wave effect is not considered,the analytical solutions for the longitudinal and axial displacements of the subway tunnel,as well as the lining axial force,shear force,and bending moment are obtained.The different internal force expressions corresponding to different foundation spring stiffness value methods are discussed.Through the analysis of the two parameters of seismic wave incident wavelength and incident angle,the expression of the wavelength and incident angle corresponding to the maximum longitudinal internal force response of the tunnel is obtained.The analytical solution is applied to an example of Xi’an subway project,and the law of the internal force and displacement of the tunnel structure with the wavelength and incident angle of the seismic wave are analyzed.Taking the Jinye 2nd Road-Zhangbalu Road section of Xi’an Metro as the engineering background,a three-dimensional finite element numerical model was established with ANSYS software.The model uses artificial viscoelastic boundaries and proportional damping.Using time history analysis to calculate the internal force and displacement responses of the tunnel structure under earthquake action.The internal force and displacement of the tunnel under the three conditions of different seismic waves,different incident angles and different segment stiffnesses are compared respectively.The response law of the tunnel internal force and displacement are obtained.Studying the damping effect of two anti-vibration measures,rubber damping layer and grouting reinforcement.Analyzing response of internal forces and displacements of the tunnel structure under different damping measures.It is concluded that the shock absorption effect of the rubber layer is better than that of the grouting reinforcement.The shock absorption effect of the 12cm～17cm rubber shock absorption layer is the best damping measures.Considering the poor durability and stability of rubber materials,rigid and flexible shock absorption measures should be taken.