Imaging Ahead of Tunnel Boring Machines With DC Resistivity
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2020-10-07
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Edition:Final Report
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Abstract:Tunnel boring machines (TBMs) are often used for underground tunneling and construction projects. However, there are dangers and risks during underground construction from unknown hazards ahead of tunneling operations, which may result in surface settlement and machine damage. Geophysical methods have the potential to improve tunneling projects by imaging the subsurface ahead of a TBM. In particular, direct current (DC) resistivity is an attractive option because the electrical conductivities of hazards such as soils, rocks, pipes, and other anomalous features vary over several orders of magnitude. The resistivity method is well understood in the context of surface and borehole geophysics, but it is seldom applied in underground construction and tunneling. Furthermore, the high conductivity of the TBM itself and the reduced number and available positions of electrodes that can be used on the cutterhead present challenges to the method. In this study, DC resistivity data are collected with model TBMs in laboratory scale environments and compared with numerical simulations for the purpose of better understanding the potential value to tunneling operations. Furthermore, we perform tests of various inversion algorithms to determine if reliable geophysical images can be produced in such a challenging environment. Overall, the experimental and numerical results show that DC resistivity is capable of detecting and imaging hazards in front of a TBM.
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