Abstract
A case study of monitoring and analysis of ground settlement caused by tunnelling of stacked twin tunnels for underground metro line construction through the densely populated area using the slurry pressure-balanced TBM is presented. Detailed ground settlement monitoring was carried out for the initial stage of down-track tunnelling in order to estimate trough width factor and volume losses including face, shield, and tail losses. In addition, using the gap model, prediction of volume loss and ground settlement was carried out with consideration of the ground condition, TBM configurations, and actual operation data. The predictions of the gap model were compared with the observed results, and adjustment factors were determined for volume loss estimation. The adjusted factors were applied to predict ground settlement of the up-track tunnel, and its results were compared with the field measurements.
Highlights
A case study of monitoring and analysis of ground settlement caused by tunnelling of stacked twin tunnels for underground metro line construction through the densely populated area using the slurry pressure-balanced tunnel boring machine (TBM) is presented
Using the gap model, prediction of volume loss and ground settlement was carried out with consideration of the ground condition, TBM configurations, and actual operation data. e predictions of the gap model were compared with the observed results, and adjustment factors were determined for volume loss estimation. e adjusted factors were applied to predict ground settlement of the up-track tunnel, and its results were compared with the field measurements
After finishing excavation at the tunnel face, the shield TBM radially supports the inside of the excavated cavity based on the reaction from the thick steel shield skin plate. en, concrete segment lining is installed just rear of the shield skin plate as a permanent ground supporting structure, where simultaneous backfilling of pressurized grout is conducted at the annulus gap around the segment lining to restrict excessive radial contraction of the excavated ground
Summary
E longitudinal pro le of the monitoring section is presented, where both the down- and up-track tunnels were driven with low ground cover through the ll, alluvium, and upper part of CDG layers, which are thought to be susceptible to settlement. Both of the tunnels were classi ed as shallow. To monitor sequentially developing settlement at each stage of TBM advance as face excavation, passage of the shield skin plate, segment ring build with tail void grouting, eleven crown settlement points were instrumented directly above the tunnel centerline. 400 kPa of pressure was consistently applied for back ll grouting to minimize ground settlement
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