Construction Parameters Control of Shield Tunnel Underneath Traversing Existing Dual Shield Tunnels

In order to investigate reasonable construction parameters of a shield tunnel underneath traversing existing dual shield tunnels, the project that shield tunnel of the East Trunk Canal of the South-to-North Water Diversion Project traversed subway shield tunnels in Beijing was studied as an example. The reason for the difference in settlement between the left and right tunnels was determined by analyzing the numerical simulation and in situ monitoring data of the settlement of existing tunnels and the shield construction parameters. Then, the construction parameters for controlling settlement were given. Moreover, the trends in the variation in settlement of existing tunnels caused by traversing construction was discussed and some measures to counter shield tunnel diseases were proposed and verified. The results show that because of the influences of shield construction with different parameters, the final settlement of the existing left tunnel is 23.9 mm, while that of the right tunnel is only 4.8 mm. Although the settlements of the two tunnels differ significantly, their trends in variation are almost consistent. During the construction, the adjusted range of the working chamber pressure should not be more than 0.005 MPa and the synchronous grouting pressure should be adjusted accurately to be 0.50 MPa. Meanwhile, the secondary grouting pressure should be 0.20-0.35 MPa, and the tunneling speed in the curve section is required to slow down appropriately. Since the maintenance time in a subway is short, chemical grouting is adopted to solve the problem of leakage of water in segment joints and bolt holes while a pressure filling resin is used to repair the cracks in the slab.