Centrifuge modelling of tunnelling below existing twin tunnels with different types of support

Tunnel excavation below existing tunnels produces ultimate and serviceability problems to the existing tunnels. The behaviours of induced stresses on the existing tunnels haven't yet been fully recognized. In this study, a centrifuge model test was adopted to investigate the effects of new tunnelling on two existing overlying tunnels. One existing tunnel model simulated a prototype composite lining tunnel and the other simulated a prototype segmental lining tunnel. The volume loss produced by new tunnel excavation was modelled by an in-flight actuator system. The surface settlements, the existing tunnels settlements, the soil pressures on existing tunnels, the bending movements of existing tunnels, and the joint behaviours of existing tunnels were monitored. The volume of surface settlement trough was much smaller than the soil volume moving into the tunnel, due to the heave of the tunnel bottom and the dilation of sand during shearing. The maximum settlement of the segmental lining model was larger than that of the composite lining model as the equivalent bending stiffness of the composite lining model was larger than that of the former. Due to new tunnel excavation, the soil pressures on different positions of the existing tunnel behaved differently, and the bending movements of the existing tunnels decreased. Moreover, the joint deformation of existing tunnel caused by new tunnel excavation could be classified into three types: (1) translation, (2) rotation, and (3) combination of both.

Automated summary

The study used centrifuge model tests to investigate the effects of new tunneling on existing tunnels, including surface settlements, soil pressures, bending movements, and joint behaviors. The results showed that the volume loss from new tunnel excavation was smaller than the soil volume moving into the tunnel, and the maximum settlement of the segmental lining model was larger than that of the composite lining model. Additionally, the soil pressures on different positions of the existing tunnel behaved differently, and the bending movements of the existing tunnels decreased due to new tunnel excavation.