Study on the optimization of the approaching construction of the four-hole large-section municipal tunnels crossing railway tunnel

In order to analyse the safety of the two main line tunnels and two ramp tunnels crossing the existing Bajiaogou tunnel in Chongqing University City, the plane and three-dimensional models were established to study the impact on the existing railway tunnels by strength reduction method and structure analysis method. Research results: the influence of different excavation bench lengths (6m and 12m) on the existing tunnel is analysed, and suitable excavation bench length is 6m. According to the deformation rule of the lining rigid body structure, the displacement control value of the C35 lining structure is 5.9mm. Various excavation procedures have different effects on the structure and the overall stability of the surrounding rock, so optimizing the excavation process can reduce the impact of construction. Optimization principles are derived from the structural displacement time history curve of the optimal conditions. The principles: interval excavation of approaching large-section tunnels, avoiding multiple disturbances in a short time, excavating the distant tunnel before the vicinity and excavating the upper tunnel before the below. The conclusions have guiding significance for the optimization of the four large-section tunnels’ approaching construction.