A Study On Key Techniques Of Shallow Tunnelling Underneath Underground Pipes

This study investigated CRD tunneling, reinforcement and subsidence pattern by using a combined scheme of theoretical analysis, numerical simulation and field tests etc., based on the design and construction of Meiau Eighth Road Shallow Tunnel with a lot of underground pipelines, at Shenzhen Metro Line 4. The work done and major achievements are as follows.●According to the project features, two-dimensional modeling was used to analyse and optimize the excavation procedure of shallow tunneling with a rectangular section, and studied the mechanism of middle rock pillar and foot-lock anchor. It was achieved that excavating parts farther from the tunnel axis symmetrically first can minimize its influence on surrounding rocks, and the middle rock pillars and foot-lock anchors can effectively reduce ground settlement and roof deformation, etc.●Applying three-dimensional modeling, the whole process of shallow tunneling was simulated, and the stress distribution and displacement pattern before and after the removal of temporary support. It is concluded that the maximum stress occurs at area 3-4m outside the pilot tunnel, the stress concentration occurs around the intersection of temporary support and rock, and the removal of the temporary support could increase ground surface settlement over 20%.●Monitoring was carried out during the tunneling in order to monitor the ground surface settlement, deformation of initial rock support and underground pipelines. A result was obtained that at the initial stage, both ground surface velocity and acceleration increases with tunneling advance from 2D in front of the working face, the maximum ground surface velocity occurs when the excavation advanced 2D, and then ground surface velocity decreases.●The comprison of monitoring dada with modeling result showed that the monitoring data is well consistent with the modeling result, which indicates that the modeling method is effective.