Seismic Fragility Analysis of Shield Tunnel Considering the Pulse Effect and the Residual Ground Motions

Performance-based earthquake engineering research can effectively estimate the seismic risk and failure probability of structures subjected to seismic influence with a certain intensity level. When the field of tunnel is close to the earthquake source, potential near-fault pulses containing large pulse energies will cause severe threat on tunnel. Taking the near-fault pulse effects of ground motions into account, the relationship between of the push forces and intensity of the selected ground motions was built and more importantly, the seismic fragility analysis by a fabricated shield tunnel load-structure model was investigated to evaluate the seismic performance of shield tunnel. Based on the seismic fragility analysis, optional intensity index of the near-fault pulse-like ground motions was compared and selected, and seismic fragility curves of shield tunnel under the optional intensity index was obtained finally. The results show that when the near-fault pulse-like ground motion was selected as the input seismic waves, the pulse energy containing the time-histories have to be considered in the seismic fragility analysis. Affected by the strongly transverse earthquake excitation, the joints part of shield tunnel is vulnerable, especially in the left arch shoulder and right arch foot, where the bolts maintain large stress states and structure deformation. Through the comparison and selection of the optional intensity index, pulse energy presents a better double logarithmic linear fitting relationship with the structure damage index (referring to joint opening here) than peak ground acceleration and peak ground velocity when pulse-like ground motions. This research results can provide a reference for the resilient assessment of shield tunnel under strong earthquake considering pulse effects in seismic design when the tunnel site is close to the earthquake source.