Study On Seismic Response And Influencing Factors Of Shield Tunnels

With the rapid development of China’s economic in recent years,urbanization are accelerating significantly increased, which lead to pressure onurban traffic. so metro has become the inevitable choice to solve the trafficcongestion. Many cities in China subway began operating. Thereforeresearching the reaction rules and influencing factors of shield tunnel hasbecome a very important issue. In this paper, seismic response of shield tunnel,seismic influence of tunnel depth as well as tunnel spacing are studied usingthe finite difference software FLAC2D. The specific contents are as follows:1This selection introduces the principle of finite difference calculationsand Mohr-Coulomb model implementation in the FLAC2D. For artificialboundary problem, the validity of FLAC artificial boundary has been verifideby input pulse wave. This selection also introduces Rayleigh dampingparameter selection method and the influence of the smallest center frequencyselection for the free-field.boundary.2The methed of initial stress field formation for shield tunnel isintroduced in this section. Elastic and plastic dynamic response of the model isanalysised by inputing horizontal and vertical component of El-Centro waverespectively. Make diagram of inner forces and envelope diagram, underdifferent conditions. Tunnel under the effect of initial stress and seismic stressincrement in combination are analyzed.3Tunnel stress increment with the depth variation is studied, with theinputs of the El-Centro wave, Taft wave, Qianan wave, using the elastic andplastic constitutive model. The results show that: When not consider the initialin-situ stress, the type of seismic waves affect the internal forces of the tunnelunder different depth，different spectral components of the seismic waves willappear different variation. The incremental of axial force decreases slightlywhile shear force and moment increases with the increasing tunnel depth.4Due to the scattering of seismic waves between two tunnels, earthquakeinduced double tunnels’ peak internal force is larger than single tunnel.Dynamic response of two parallel tunnels at different spacing and the impact ofpeak ground acceleration on the top of the tunnel are studied in this section.The following conclusions: When the spacing of two tunnels between one times of tunnel diameter, it has a large mutual influence, which should beconsidered in the design of tunnel. For up and down parallel tunnels, the uppertunnel sufferde larger earthquakes impact than the down tunnel. The existenceof tunnel of will impanct the earth’s surface ground motion which may causeground peak acceleration increases in some parts of the surface. The impact ofparallel tunnel is larger than the single tunnel. Within a certain tunnel space,the midpoint of two tunnels above the ground has the maximum peakacceleration, which doubled the single tunnel.