Comprehensive health assessment of shield tunnel structure based on prototype experiment

Health state of shield tunnels is one of the most important parameters for structure maintenance. Usually, the shield tunnel is extremely long in longitude direction and composed by many segments. It is difficult to quantify the relationship between the structure damage state and shield tunnel structure deformation by the model test because of unpredictable effects of different scales between model test and prototype tunnel structure. Here, an in-situ monitoring project was conducted to study the excavation induced shield tunnel structure damage, which could be considered a prototype test on the tunnel deformation. The disaster performance of tunnel leakage, segment crack, segment dislocation and segment block drop-off during longitude deformation and cross-section ovality developments was analyzed. The results indicate that instead of the longitude deformation, the ovality value has the strongest correlation to the rest disease performance, which could be used as the assessment index of the tunnel health. For this tunnel, it is in health state when the ovality is less than 0.5%, and the serious damage could be found when the ovality value is higher than 0.77%. The research results provide valuable reference to shield tunnel health assessment and help complete the standard of shield tunnel construction.