![]() ![]() Then, 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 also conducted at the annulus gap around the segment lining to restrict excessive radial contraction of the excavated ground. ![]() 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. First, the TBM excavates ground using a disc cutter or cutter bits mounted on the rigid steel cutterhead and imposes earth pressure or slurry pressure on the tunnel face to prevent squeezing movement of ground towards the tunnel face. Compared to the conventional drill and blast tunnelling method, the shield TBM tunnelling has several advantages in the control of ground settlement. ![]() ![]() The closed-type shield tunnel boring machine (TBM) has been widely applied to the tunnelling works in urban area to minimize impact of tunnel construction on the adjacent facilities and buildings. The adjusted factors were applied to predict ground settlement of the up-track tunnel, and its results were compared with the field measurements. The predictions of the gap model were compared with the observed results, and adjustment factors were determined for volume loss estimation. 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. 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. 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. ![]()
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