Numerical study of the Soil-Tunnel and Tunnel-Tunnel interactions of EPBM overlapping tunnels constructed in soft ground

The tunnels between the Chenglinlu station and Jintanglu stations of Tianjin Metro line 5 are by far the longest overlapping tunnels in China. The tunnels were constructed with earth pressure balanced machines (EPBMs) in soft ground. A greenfield site was selected and densely instrumented to conduct field research. Based on the certain site, a three-dimensional numerical model was developed to investigate the soil-tunnel and tunnel-tunnel interactions. The ground surface settlements developed during each phase of EPBM advancement were analyzed and discussed. Two cases: upline tunnel constructed as a second tunnel and upline tunnel constructed as a single tunnel, were compared. The presence of downline tunnels reinforces the ground underneath upline tunnel while the construction process of downline reduces the soil stress at upline position. Overall, upline tunnel constructed as a second tunnel has a smaller maximum settlement. The influence of upline tunnel construction on downline tunnel lining force was investigated. Upline tunnel construction does not cause additional risk for segment rings of downline tunnel, and the primary focus on downline tunnel safety should be on segments floating and dislocation.