5:15 PM - 6:45 PM
[HTT18-P02] Repeated measurements of electrical resistivity of shallow part in leaky sections of tunnel ground
Keywords:electrical resistivity, leaky sections, tunnel
The amount of groundwater within the tunnel ground changes depending on the supply of rainfall and snowmelt water, and during periods of high water flow, water may appear as leaks inside the tunnel. Water leaks can deteriorate equipment and affect safe vehicular passage. Therefore, it is necessary to investigate the characteristics of groundwater and take countermeasures. In order to understand changes in groundwater within the tunnel ground, we conducted repeated electrical surveys of the shallow ground beneath the tunnel's roadbed and investigated time-series changes in resistivity values in leakage sections.
The survey was conducted in a decommissioned road tunnel with a length of 1.9 km located on the Sea of Japan coast of Hokkaido, Japan. The main geology of the tunnel ground is altered andesite, tuff breccia, and andesite lava. The authors conducted electrical resistivity survey and a boring survey on the paved surface of this tunnel to estimate the geological properties in the shallow part of the ground. Based on these results and the occurrence of water leakage, two sections (section A is 180 m, and section B is 180 m) were determined. The resistivity of section A is 20 to 300 Ωm, and that of section B is 50 to 350 Ωm. Apparent resistivity values were calculated from measurements using the Wenner method once a month in these sections from May 2019 to January 2021. The electrode spacing was 6 m, the exploration depth was 6 m, and measurements were taken at 30 points in both sections.
As the results of survey, points with large changes in the repeatedly measured resistivity values corresponded to sections where water leakage panels were installed. In addition, the results of resistivity measurements in previous years corresponded to points where continuous changes in resistivity values were observed, and points where low values were observed in areas where high resistivity values continued. It was found that at points with such a resistivity distribution, differences in groundwater supply may occur depending on the season.
The survey was conducted in a decommissioned road tunnel with a length of 1.9 km located on the Sea of Japan coast of Hokkaido, Japan. The main geology of the tunnel ground is altered andesite, tuff breccia, and andesite lava. The authors conducted electrical resistivity survey and a boring survey on the paved surface of this tunnel to estimate the geological properties in the shallow part of the ground. Based on these results and the occurrence of water leakage, two sections (section A is 180 m, and section B is 180 m) were determined. The resistivity of section A is 20 to 300 Ωm, and that of section B is 50 to 350 Ωm. Apparent resistivity values were calculated from measurements using the Wenner method once a month in these sections from May 2019 to January 2021. The electrode spacing was 6 m, the exploration depth was 6 m, and measurements were taken at 30 points in both sections.
As the results of survey, points with large changes in the repeatedly measured resistivity values corresponded to sections where water leakage panels were installed. In addition, the results of resistivity measurements in previous years corresponded to points where continuous changes in resistivity values were observed, and points where low values were observed in areas where high resistivity values continued. It was found that at points with such a resistivity distribution, differences in groundwater supply may occur depending on the season.