Examining the influence of TBM-ground interaction on electrical resistivity imaging ahead of the TBM

摘要

Tunnel excavation by means of tunnel boring machines (TBMs) is susceptible to unknown changes ahead of the tunnel face. Geophysics. offers a technique called electrical resistivity that can continuously, in real-time, spatially map the formation in front of the TBM. Electrical resistivity has been successfully established for many applications including vadoze zone hydrology, oil/gas location, mineral location and failure detection in geo-structures. Yet it has not been well-established for TBM excavations. This is in part due to the complexity of the TBM tunneling environment and the uncertain influence this environment may have on the success of TBM-integrated-electrical resistivity to predict changes ahead of the tunnel face. One significant uncertainty lies in the interface region that exists around the TBM created during the modification of the virgin formation by a mechanical mixing action of the rotating cutterhead and the injection of additives used to aid in the extraction of the muck and protect the cutting tools from frictional wear. In this study, we investigate the influence of this interface region on TBM-integrated-electrical resistivity for both hard rock and soft ground tunneling conditions through finite element modeling. Regarding the performance of TBM-integrated-electrical resistivity to detect changes ahead of the cutting face, the interface region holds significant influence for both earth pressure balance (EPB) and open mode tunneling conditions. Electrical resistivity for slurry based tunneling is not influenced by the interface region. Simulations suggest that TBM-integrated-electrical resistivity can be sensitive to a formation change that is located up to five diameters in front of the TBM. (C) 2016 Elsevier Ltd. All rights reserved.