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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]

Summary: As numerical models are increasingly used as a design tool in geotechnical engineering, it is highly desirable if geotechnical reliability analysis can be conducted based on numeral models. Currently, the practical use of geotechnical reliability analysis‐based numerical models is still quite limited. In this study, an easy to access method is derived to conduct geotechnical reliability analysis based on numerical models. To facilitate its application, a procedure is outlined to implement the suggested method such that geotechnical reliability analysis can be automated using existing geotechnical numerical packages. The procedure is illustrated in detail with an example, and the source codes provided can be easily adapted to analyze other similar problems. The method described in this paper is used to study the reliability of a deteriorating reinforced concrete drainage culvert in Shanghai, China. The suggested method provides a convenient means for reliability analysis of complex geotechnical problems. [ABSTRACT FROM AUTHOR]