Seismic fragility analysis of in-service shield tunnels considering surface building and joint-bolt corrosion

Abstract

The present study aims to assess the seismic fragility of shield tunnels in the transverse direction based on investigating seismic performance of segments and joints, accounting for the effects of the later-built surface structure and corrosion of joint bolts. To this end, the tunnel-soil-surface structure interaction and joint-bolt deterioration due to corrosion are examined. The surface structure is assumed to be a ten-story three-span reinforced concrete frame building on a raft foundation, and the corrosion effects of steel joint-bolt are reflected by reducing the cross-sectional area and strength. The seismic performance of shield tunnel, including the plastic strain of tunnel lining, joint deformation and bolt damage, are investigated by incremental dynamic analysis (IDA) through a verified finite element approach. The damage state levels are divided by the segment damage of the lining concrete and joint deformation, according to the seismic performance and subway protection codes. The fragility curves for shield tunnel are derived and the tunnel vulnerability is evaluated. The results indicate that the shield tunnel is more vulnerable under the coupling effects of surface building and earthquake loading. The damage probabilities of the tunnel structure obviously accelerate with the development of bolt corrosion when the corrosion rates increase from 10% to 20%–30%. The influence of bolt deterioration on tunnel damage should receive more attention with the increase in the operation period. Finally, the fragility curves without the surface building and corrosion of joint bolts are compared with empirical results.