Numerical Simulations of Construction of Shield Tunnel with Small Clearance to Adjacent Tunnel without and with Isolation Pile Reinforcement

In the process of building subways in many cities, the technology of shield tunneling has become more widely used. In large cities, it is inevitable for the tunnels to pass through the foundations of buildings or between deep piles of bridges. Due to the many restrictions on urban space in China, the clearance between two tunnels has also become smaller. Hence, it is an urgent technical problem to resolve the mutual influence of the close construction of two tunnels using shield technology. In this study, the shield construction project of two tunnels with a small clearance of 2.6 m has been analyzed. The project is between Tongdewei Station and Shangbu Station in the northern extension section of the Guangzhou Metro Line 8. The main parameters used in the analyses are the tunnel lining deformation and the ground settlement. The construction without and with the isolation pile reinforcement have been simulated numerically. The simulation results have been compared with the on-site monitoring data. Based on the comparison, it shows that with the reinforcement, the tunnel lining deformation and the ground settlement can be reduced significantly. The effect of subway shield construction on the construction of the first subway tunnel will significantly reduce. The deformation of the shield excavation net width and the mutual influence can also be greatly reduced. The findings from this study can be used as technical foundation and reference for the construction of similar projects, i.e. shield tunnel construction with a small clearance between tunnels.