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Accidental surcharges caused by unauthorized damped waste are the most serious hazard threatening the serviceability and structural safety of shield tunnels in Shanghai, China. It is highly desirable to assess the effect of such accidental surcharges on the performance of shield tunnels. Nevertheless, the occurrence and magnitude of the accidental surcharges are both highly uncertain. In this paper, a probabilistic method is suggested to evaluate the performance of shield tunnels subjected to accidental surcharges, which can systematically consider the uncertainty in the soil properties, the uncertainty in the magnitude of the accidental surcharges, and the uncertainty of the occurrence of the accidental surcharges. The suggested method is used to analyse the potential effect of accidental surcharges on the safety of tunnels in Shanghai. It is found that the maximum height of the surcharges and the mean rate of the surcharges can significantly affect the performance of shield tunnels. Considering the past performance of shield tunnels can increase our confidence in the future performance of the tunnels. The suggested method provides a practical means to quantify the risk posed by the accidental surcharges to the performance of the shield tunnels. [ABSTRACT FROM AUTHOR]

An underground passage is constructed in the Bund, Shanghai, which intersects an existing shield tunnel, the East Yan'an road tunnel. This research reports a series of centrifuge model tests conducted to investigate the effect of deep excavation above an existing tunnel. The results reveal that significant tunnel heave can be observed, induced by excavation above. For the test conducted to model the East Yan'an road tunnel, the influenced range of the tunnel extends to about 2·5 times the excavation width away from the boundary of the excavation. Considerable additional bending moments are observed at the crown and invert in the lining of the tunnel below the centre of the excavation, but the additional moments rapidly decrease to be negligible when the tunnel cross-section is 1·5 times the excavation depth away from the centre of the excavation. It is also found that the longitudinal deflection of the tunnel due to excavation above it can be modelled by a Gaussian curve, based on which the location of the inflection points and bending curvature can be obtained conveniently. Comparing tests with different tunnel positions, the tunnel heave decreases exponentially with the tunnel-excavation offset. [ABSTRACT FROM AUTHOR]