Seismic Safety Analysis Method Of Underground Tunnels

In recent years, with the rapid development of metro construction in our country, the seismic analysis safety of underground subway structures has been paid wide attention.China is an earthquake-prone country, so seismic safety analysis of underground tunnels has great significance to the development of the anti-earthquake design method of underground structures.This paper presents Seismic safety analysis of underground tunnels based on the viscous-spring boundary and equivalent node force of earthquake excitation, implemented with general finite element analysis software ANSYS. The model is validated through comparisons with the results in literature. A case study is conducted with metro twin tunnels under thick soil layers in Tianjin City, in which both linear and nonlinear seismic responses are analyzed. In the nonlinear model, an equivalent linear method is used, considering the nonlinearity of concrete and reinforcement separately as well as the contact between soil and liner. The results contain the liner seismic stress histories and peaks for different tunnel intervals. After that, 30 artificial ground motions having the identical statistical feature, time-dependent power spectrum, with El Centro wave are applied to the narrow spacing model and the results are analyzed statistically.Research shows that tunnel interval has a significant effect on the seismic stresses in tunnel liner. There is evident interaction between two tunnels when the two tunnels are close, and the maximal principal seismic stresses are increased significantly and located between two tunnels. Compared with the case of single tunnel, the maximal principal seismic stresses of metro twin tunnels are increased by up to 37%. This model can be used for seismic analysis of underground tunnels in complex sites.