Coupling Failure Mechanism of Underground Structures Induced by Construction Disturbances

The development of cities often involves the construction of new tunnels buried underneath densely distributed existing structures. When tunnels experience complicated and difficult conditions, coupling failure mechanisms often develop, in which the failure of one structure results in the failures of adjacent structures caused by soil failure initiated from the excavation of the new tunnel. Four centrifuge tests were performed in this study to reveal three major mechanisms, i.e., rapid sand flow, partial failure and overall collapse induced by the instability of a tunnel face and the effects of soil types and buried existing structures. Data are presented about the deformation and the failure mechanisms. Effects of soil properties and groundwater are discussed. The tests indicate that rapid sand flow can be easily triggered by tunnel face instability, a chimney-like mechanism creating gaps underneath existing structures. In cohesive soil, failure may be limited in front of the tunnel face due to the formation of arching, rendering a partial collapse. An overall collapse may occur in less cohesive soil when involving changes in underground water, which is a failure mode of a ground block bounded by two single shear planes extending from the tunnel face to the surface. It was observed that the bending deformation of the existing tunnel is well correlated with the failure mode, and a limited partial collapse had the smallest impact on the tunnel. The magnitude of the deformation of the structures depended not only on the failure mode but also on the scope and orientation of the failure.