Abstract
A rectangular pedestrian underpass of 94.5m long, 7m wide and 4.3m high was constructed across the existed metro tunnels using pipe jacking method. The minimum distance from underpass bottom to tunnel crown was 4.5m. In order to investigate the effects of pipe jacking on existed underlying tunnels, the instruments were installed in the tunnels and structural responses were extensively monitored. Based on the field observations, the vertical displacement, horizontal displacement and diameter convergence of the tunnel were analyzed. The results indicate that in the whole pipe jacking process, the tunnel vertical displacement mainly goes through three different stages, namely, initial settlement stage, quick heave stage and steady heave stage. The horizontal displacement of ballast bed is much smaller than that of tunnel crown and is almost negligible. The tunnel was horizontally compressed and vertically stretched after pipe jacking construction. Pipe jacking construction has a greater effect on the tunnel structures just below the underpass than that beyond the width scope of underpass, whether it is vertical displacement, horizontal displacement or diameter convergence of the tunnel.
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