Abstract: The purpose of this study is to guarantee the safe operation of tunnels by identifying the disturbance of new tunnel construction to existing tunnels. The construction of Beijing Metro New Airport Line overcrossing the existing Metro Line 10 tunnel was taken as a case study. The disturbance was simulated using FLAC^3D with varying burial depth and clearance of the existing tunnel. According to the control value (2 mm) and warning value (1.4 mm) of vault displacement control standard for the existing tunnel, the disturbance impact zone was divided into strong impact zone, weak impact zone and non-impact zone. Furthermore, according to the construction impact zoning and engineering characteristics, two reinforcement measures were proposed and numerically simulated. The two measures are: advance pipe curtain, and advance pipe curtain plus soil grouting. Results demonstrate that the control effect (vault displacement reduction rate) of advance pipe curtain is 64.05%, while the advance pipe curtain plus soil grouting 70.23%. Considering on-site control standards, we recommend that the advance pipe curtain plus soil grouting could ensure the construction safety of the new tunnel and the operation safety of the existing tunnel as well.

Key words: subway tunnel, super-close overcrossing, FLAC^3D software, construction impact zoning, reinforcement measures