The Influence of Non-synchronous Excavation of Twin Curved Shield Tunnels

Abstract

The theoretical model of twin curved shield tunnels and refined numerical model considering the characteristics of wedge-shaped segment ring joints were established in this paper. Two construction schemes of taking the inner side or outer side of the twin curved tunnels as the first tunnel were conducted for comparison. Then two main characteristics of curved tunnel construction (over-excavation and yaw excavation loadings) were taken as variables to explore their response to the approaching construction caused by unsynchronized driving of twin curved shield tunnels. The ground surface settlement troughs obtained by the analytical solution and numerical simulation are in good agreement with the monitoring result. On the condition that the curved tunnel at the inner side is taken as the first tunnel, the excavation will intensify the ground settlement and the internal forces of its segment. In the case that the overcutting gap is not of large volume, it is advisable to first excavate the curved tunnel at the outer side, and then construct the curved tunnel at the inner side. The influence of soil loss on the ground disturbance is greater than that of construction loadings. The excessive overcutting gap not only easily induces a sharp increase in the ground vertical displacement, but also may lead to the movement of soil at the inner and middle sides towards the inner side of the curved tunnels, and causes the soil at the outer side to move towards the outer side of the curved tunnels. Remarkably, excessive overcutting gap may lead to large horizontal displacements of the ground surface.