Centrifuge modelling of deep excavation over existing tunnels

Abstract

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.