Dynamic Response Of Shield Tunnel Under Earthquake Action And Safety Analysis Of Seismic Crack Structure

With the continuous development of social economy and the increase of urban population,in order to alleviate the traffic pressure,all major cities are developing subway projects,and the construction of tunnel shield method has been widely used.However,China is located between the two major seismic zones in the world,and seismicity is very active.Due to the late start of large-scale underground structure construction in China,the seismic data and data collected are not enough,and the seismic study of subway shield tunnel is not deep enough.In view of this,this article on the basis of previous studies,taking a subway shield tunnel as the background,based on the finite element theory and the basis of the principle of extended finite element method,established the intensification of shield tunnel-analysis model of surrounding rock.By applying seismic shear wave of different types and intensities,the dynamic response of tunnel lining and the characteristics of concrete crack propagation are studied.Based on the above analysis,the main research contents and results are as follows:(1)The finite element analysis model of shield tunneling and surrounding rock was established,and the stiffness equivalent test principle of orthotropic concrete material was put forward.By means of the numerical loading test,the horizontal and longitudinal stiffness reduction coefficients of the whole performance are considered.(2)Seismic waves attenuate rapidly when propagating in the stratum,and there are obvious surface amplification effects.The acceleration response of the lining is closely related to the vibration response of the ground.Under the effect of shear wave,the hoop stress response of the lining concrete is significant,the fluctuation of 45 ° to produce stress concentration near the arch shoulder and arch foot.It will produce ? type crack when the largest tensile stress more than material allowable tensile strength,and crack distribution in the inside lining.With the increase of seismic intensity,the cracking time of concrete is much earlier,the number of cracks is more,and the tunnel is more damaged.(3)The analysis model and structural safety analysis method of the crack lining are established.Finite element method is used to calculate the tensile stress of the crack tip and compared with the allowable tensile strength of concrete to analysis of crack stability.Through the calculation of the section strength,the bearing safety coefficient of the cracked section is obviously reduced,but the lining bearing capacity still meets the requirements.