Research On The Dynamic Response Of Metro Tunnel Under Earthquakes

With the rapid development of subway construction in China, lots of urgent problems about seismic research and design of the structure in the subway tunnel construction need to be solved in theory and practice in highly seismic region. Combined with the Xi'an metro, by using the large finite difference software FLAC3 D, the influence of depth of tunnel, seismic wave intensity, vibration direction, lining parameters, the distance between two tunnels and strata conditions on the seismic response of metro tunnel under earthquake are studied. The main research results are introduced as follows:First, based on the analysis of soil dynamic constitutive model, the theory of finite difference method and the nonlinear dynamic analysis are introduced, which provide reference for dynamic response analysis of metro tunnel under earthquakes by using FLAC3 D.Second, based on the single hole tunnel in Xi'an metro, the influence of the parameters such as tunnel depth, seismic wave, vibration direction, lining thickness and concrete strength on the seismic response of metro tunnel are also analyzed. The result shows that with the influence of the seismic wave E3, the peak displacement of tunnel structures increases about 193.33% compared with the influence of the seismic wave E2,and the maximal principal stress and the minimum principal stress increase about 211.0% and 107.64% respectively; with the increase of concrete strength and lining thickness, the peak displacement of tunnel structures will decease and the stress of lining structure will increase gradually; the displacement and stress of lining structure with the influence of seismic wave generated from X direction is relatively large and the X direction is bad to the aseismatic performance of tunnel structures; when the tunnel depth increases from 1D(D is the diameter of tunnel) to 6D,the peak displacement of tunnel structures will decrease about 8.89%?6.43%?2.53%?3.13%?37.33% correspondingly, and the maximal principal stress of lining structure will increase accordingly.Third, based on the double hole tunnel, the influence of horizontal spacing changes of the double subway tunnel and small duct grouting reinforcement of surrounding rock on the seismic performance of subway tunnel is analyzed. With the increase of the horizontal distance of the two tunnels, the peak displacement of tunnel structure decreases gradually as a whole and the maximal principal stress of tunnel structure also decreases gradually, and when the horizontal distance of the two tunnels is longer than 2.5D, the maximal principal stress of tunnel structure tends to be stable. The peak displacement of tunnel lining structures decreases accordingly after the surrounding is reinforced by the little tremie grouting, and the peak displacements in X direction of arch bottoms in left hole and right hole decrease 8.36%?2.32% respectively, and the peak displacements in Y direction of arch bottoms in left hole and right hole decrease 1.78%?2.53% respectively; the peak values of the maximal and minimum principal stress decrease 1.83% and 10.14% accordingly, and it is beneficial for the aseismatic performance of tunnel structures. The research results provide some references for the seismic design of subway tunnel.