Shanghai Jiaotong Daxue xuebao (Dec 2023)
Observed Environment Response Caused by Construction of Double-Line Parallel Pipe Jacking Crossing over Metro Shield Tunnels
Abstract
Based on the field measured data of a double-line parallel power pipe jacking upper span subway shield tunnel, the environmental impact of a short-distance double-line pipe jacking in sandy silt stratum in the process of crossing over the existing subway tunnel was analyzed in detail, including the transverse surface settlement distribution, the development of settlement with time, and the floating of subway tunnels. The results show that the horizontal surface settlement curve of single pipe jacking presents a “V” shape, while the horizontal surface settlement curve of double line pipe jacking is an asymmetric “W” shape. The settlement of ground surface above the axis of the later pipe jacking is larger than that of the first pipe jacking. During the construction of the later pipe jacking, the settlement above the axis of the first pipe jacking is also obvious. The Peck formula has a good applicability in predicting surface settlement curve caused by pipe-jacking construction. For single-line pipe-jacking, the width parameter of settlement trough is 0.79, and the ground loss ratio is 1.6%. For double-line pipe jacking, the width parameter of settlement trough of the first and later pipe jacking are 0.74 and 0.58 respectively, and the former is 1.28 times of the latter. The soil loss ratio of the first and the second pipe jacking are 2.41% and 3.11% respectively, and the latter is 1.29 times of the former. Pipe jacking causes the vertical displacement distribution curve of the “W” shape in the longitudinal direction of the underlying subway tunnel. There is a lag in the up-floating of the tunnel after the completion of pipe jacking crossing. The longitudinal influence range of the parallel pipe jacking construction on the subway shield tunnel is about 4~6 times the pipe jacking diameter. The instantaneous settlement generated by the later pipe jacking across the monitoring section is greater than that generated by the first pipe jacking. The permeability of the undisturbed soil is reduced when the silty soil above the tunnel is pre-reinforced by the metro jet system (MJS). The ground settlement will continue for a period of time after the pipe jacking crossing. The exponential function can be used to describe the development of the settlement with time after the instantaneous settlement occurs.
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