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| | Abstract | | Engineering geophysics has played an important role in planning and constructing of mountain tunnels. Moreover, recent increase in collapses occurred in active tunnels has led us to utilize geophysics for the safety check of existing tunnel structures. Besides the estimation of thickness of concrete lining and detection of voids behind the lining, measurements for the concrete pavements and tunnel formations is one of the major targets of the safety check of tunnels. We conducted field measurements in an abandoned tunnel to evaluate geophysical methods for the characterization of the basement structures of tunnel. Tested methods were capacitively coupled resistivity measurement using OhmMapper and high-frequency surface wave measurement. As a result, near surface structures up to 20 m beneath the tunnel floor were clearly imaged. The reconstructed structure was concordant with excavation and maintenance history of the tunnel. Furthermore, the reconstructed geophysical sections matched with a previously reported P-wave velocity section. In conclusion, combined resistivity and surface wave survey is capable for the evaluation of physical properties of basement structure and surrounding rocks of tunnels. |
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