Surface Settlement Control in the Excavation of a Shallow Intersection between a Double-Arched Tunnel and a Connection Tunnel

Abstract

Ground surface settlement induced by shallow tunnel construction is inevitable, and it is more complicated at the intersection area since the rock behavior is a complex, three-dimensional problem. This paper presented a case study of controlling the surface settlement during the tunneling of an urban shallow intersection between a double-arched tunnel and a connection tunnel in China. Various construction measures, including the sequence excavation, presupport, and primary support systems, were used to control the settlement. Furthermore, a three-dimensional analysis was conducted to investigate the settlement characteristics in different stages, the optimum excavation spacing among pilots, and the support effect of the presupport. The results showed that the settlement was mainly caused by the excavation of the upper steps. The deformation induced by transverse guide tunnel T3 was much larger than that of the others because the surrounding rock at the vault was plain fill. The three-pilot excavation methods can effectively control the surface settlement for a double-arched tunnel, and the optimum spacing values between the different steps were obtained. The reduced proportions of the advanced small pipes supporting construction tunnels T2 and T3 were approximately 27.0% and 17.2%, respectively, while the reduced proportion of the pipe roof supporting T4 was approximately 42.4%. The monitoring results showed that this project was successfully completed.