Numerical Analysis on an Excavation Method Comparison for a Shallow-Buried Large-Span Tunnel

Abstract

Numerical simulations of shallow-buried, large-span tunnels have been performed in this study for tunnel excavation method selection among: (1) the both-sides heading method; (2) the three-bench temporary invert method; and, (3) the three-bench seven-step method. Stress and deformation of surrounding rock and safety of support structures have been analyzed for different methods during the excavation process, and the conclusions have been drawn as follows: (1) For the restraining effect of surrounding rock, the both-sides heading method is better than the three-bench seven-step method, and the three-bench temporary invert method is the worst; (2) Comparing to the both-sides heading method, even though the deformation of the three-bench method is larger, the stress in surrounding rock has been effectively released in this way so that the load acting on the supports will be relatively smaller. By using the pipe-roof early support technology in the three-bench method, the safety of construction can be ensured and the construction period can be reduced; (3) For the three-bench temporary invert method, since the excavation face is relatively big, the stability of the working face is poor. In addition, the assembly and disassembly for temporary invert is time-consuming with higher cost. For three-bench, seven-step method, the surrounding rock deformation of the tunnel cross-section is larger and the plastic range is wider. However, all are within the safe range and the safety of the excavation face can be ensured by the core of soil reserved in this method. Hence, the three-bench seven-step method is a reasonable method because it can accelerate the construction process and reduce cost, while ensuring the supporting structure's safety and excavation face stability.