Risk Prevention-control and Structural Safety Analysis of Multi-line Tunnel Parallel Construction in Sandstone Strata

［Objective］During the parallel construction of multi-line tunnels, the excavation of subsequent tunnels will adversely disturb existing tunnels. Compared to double-line tunnels, the disturbance caused by multi-line tunnel parallel construction is more complex, necessitating researches on risk prevention-control strategies and structural safety. ［Method］Using a rail transit interval line and depot station underground excavation tunnel project as example, risk identification, prevention-control and safety analysis are conducted. The structural reliability criteria are used to quantify and determine highly affected areas during three-line tunnel parallel construction. The risk prevention-control measures for existing underground excavation tunnels in these highly affected areas, specifically in-tunnel reinforcement measures are introduced. A three-dimensional refined numerical model is established, the land subsidence and existing tunnel stressed deformation corresponding to different stages of tunnel parallel construction are analyzed, and the structural safety states and reliability of reinforced measures are evaluated. ［Result & Conclusion］Existing underground excavation tunnels with small clearance exhibit significant displacement and deformation during the excavation of the right-line shield tunnel. The disturbance impact caused by the subsequent shield tunnel decreases significantly as the distance from the preceding tunnel increases. The overall reinforcement measures using cross braces and arch canopies can effectively mitigate the additional deformation and stress on existing structures caused by the disturbance of subsequent shield tunnel construction.