In order to ensure the safety of metro tunnel construction and reduce the impact on existing buildings (structures) and traffic lines, relevant scholars have conducted a lot of research studies on metro tunnel underpassing projects and corresponding control measures. Therefore, it is necessary to study the impact of metro tunnel construction on the existing buildings (structures) and traffic lines and the corresponding construction control countermeasures. During the construction of metro tunnels, it is very easy to cause large surface settlement, which will threaten the safety of existing buildings (structures) and traffic lines on the upper part. Newly built metro tunnels underpassing through the upper existing buildings (structures) and traffic lines are common engineering problems in urban infrastructure construction.
The results show that the reinforcement scheme can effectively control the surface settlement value within the limited value (16.47 mm), which is close to the maximum surface settlement of 18.31 mm after the metro tunnel excavation is completed, indicating that the proposed reinforcement scheme is beneficial to ensure the safety of metro tunnel construction and the driving safety of the expressway. Moreover, the excavation process of the metro tunnel with and without reinforcement schemes is numerically simulated. On this basis, the control measure for strengthening the three-line tunnels with advanced small pipe grouting and reinforcing the middle tunnel with concrete-filled steel tube piles are proposed. However, the surface settlement under the optimal excavation sequence exceeds the limit value of 30 mm, which cannot guarantee the safety of expressway traffic. The numerical simulation results showed that Case 1 is the optimal excavation sequence of the metro tunnel. The influences of excavation sequence on the tunnel surrounding rock deformation, surrounding rock stress, supporting structure stress, plastic zone, and surface settlement are analyzed by using MIDAS/GTS NX finite element software. The Chongqing metro line 6 underpass expressway around the city is taken as an engineering background, and the optimal excavation sequence and corresponding control countermeasures for the triangular-distributed three-line metro tunnel underpass expressway are studied.
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