Construction Technology on Large Diameter Shield for Little-Distance Overlapped Tunnel of Metro Section with Low Gas in Metro

The construction technology of overlapping tunnels is studied, which are composed of the shield section tunnels between Tianfuxin Station and the entrance of Longquanshan Tunnel and the tunnels connected to Hejiang Vehicle Depot on Chengdu Metro Line 18. The construction measures of overlapped tunnels is put forward, which are control parameters of shield driving for lower tunnels, and grouting reinforcements of surrounding rock of lower tunnels and the sandwich between upper and lower tunnels, and the segment support structure in the lower tunnel, and control parameters of shield driving for upper tunnels. The construction technology on large diameter shield for little-distance overlapped tunnels of metro section with low gas is established. The feasibility of the established technology is verified after analyzing monitoring results of stresses of the segment support structure, the ground settlement and the deformation of the segment structure of lower tunnels. The construction task is completed safely and quickly after this technology applied, which can provide references for similar projects in the future.