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  Field study on tunnel lining resilience under extreme surcharge

  The rail transit (metro) system in metropolis is one of the best solutions to relieve the congested transportation pressures. In Shanghai, the metro system with a 538km of mileage takes up 43% of daily public transportation volume. In operating such a huge system, the safety of tunnel lining structures subjected to any unexpected hazards is badly concerned by the government and the engineers. Chang et al. has reported a field case of a shield tunnel for Taipei Rapid Transit System (TRTS) disrupted by adjacent deep excavation. Large tunnel deformation was measured and the cracks at crown was observed. A road tunnel in Taipei was found to be affected by the slide of a neighboring slope causing the severe concrete cracks of the linings . Three road tunnels in Korean with severe structural defects caused by environmental disturbance were presented in the paper by Choo et al. . In Shanghai, unfortunately, some human-related hazard, from time to time, is found to act on the tunnels. Fig. 1 shows a pie chart for these recorded human-related hazards from 2004 to 2013, statistics from personal communication with Shanghai Metro Co., Ltd. It is clear that the extreme surcharge, caused by the dumped soils loaded on the ground surface without permission, is the most significant type of human hazard. A metro shield tunnel in Shanghai was found to experience a large deformation caused by the unexpected extreme surcharge . Serious structural defects and the fracture of the steel bolts connecting adjacent lining segments were detected in this tunnel. The vulnerability of the tunnel subjected to the extreme surcharge and the recovery from such a disaster are the key aspects for a lifetime performance assessment. These two aspects compose the basic concept of a system resilience, which is receiving increasing attentions these days . However, the study on the system resilience still remains at the stage of conceptualization so far . In view of this situation, this paper presented a quantitative assessment of the tunnel lining resilience due to the extreme surcharge by using the measured data from the real case based on the one presented by Wang and Zhang . First, a general definition of the tunnel resilience is established. The tunnel performance is characterized and the resilience index is defined. By probing into the field case and monitoring data, the vulnerability and the recovery of the tunnel performance is then calculated. The corresponding resilience index is thus obtained using the general metric of the resilience. Finally, some key

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