2:00 PM - 2:15 PM
[HTT18-02] Investigation of ground structure with leak areas using electrical resistivity method and ground penetrating radar
Keywords:river levee, seepage, electrical resistivity method, round penetrating radar
In the Nagai area of Kitagawa Town, Miyazaki Prefecture on the left levee of the Kitagawa River, which is the subject of this report, leakage occurred by heavy rains in September 2022 and damaged over a wide area of cultivated field. It is considered that the river water level rose due to heavy rain and the river water seeped into the foundation and caused sand boiling. We have already reported a case in which the seepage route of river water was estimated through a non-destructive survey using electrical resistivity method on the river levees and foundations. In this report, we surveyed an electrical resistivity method on the cultivated land where the sand boiling occurred, and also surveyed ground-penetrating radar using a hyper-stacking antenna with an excellent signal-to-noise ratio at a deeper depth than conventional antenna, and compared the results with the distribution of the sand boiling.
Figure (a) shows the survey area and the layout of the survey lines for electrical resistivity method and ground-penetrating radar. The survey line of electrical resistivity method was set along the downstream direction of the river, passing through near the sand boiling. The electrical resistivity method was performed using the dipole-dipole method, with electrodes placed at 1 m interval, with a maximum of 64 channels and a maximum isolation factor of 12. The ground-penetrating radar was carried out to cover the cultivated land where the sand boiling occurred.
Figure (b) shows the positional relationship between the electrical resistivity section (color contours), the geological strata boundary estimated from ground-penetrating radar records (a red line) and the sand boiling. The stratum boundary investigated by ground-penetrating radar records roughly corresponds to the boundary of about 1000 Ωm in the electrical resistivity section. It is suggested that the shallower part of this stratum boundary is a low resistivity layer with many fine grain components and the deeper part is a high resistivity layer with many coarse grain components. As a result, as in this report, it was assumed that there is a low electrical resistivity region in the deep part, and that the sand boiling occurred where the low electrical resistivity layer on the surface layer was thin.
Figure (a) shows the survey area and the layout of the survey lines for electrical resistivity method and ground-penetrating radar. The survey line of electrical resistivity method was set along the downstream direction of the river, passing through near the sand boiling. The electrical resistivity method was performed using the dipole-dipole method, with electrodes placed at 1 m interval, with a maximum of 64 channels and a maximum isolation factor of 12. The ground-penetrating radar was carried out to cover the cultivated land where the sand boiling occurred.
Figure (b) shows the positional relationship between the electrical resistivity section (color contours), the geological strata boundary estimated from ground-penetrating radar records (a red line) and the sand boiling. The stratum boundary investigated by ground-penetrating radar records roughly corresponds to the boundary of about 1000 Ωm in the electrical resistivity section. It is suggested that the shallower part of this stratum boundary is a low resistivity layer with many fine grain components and the deeper part is a high resistivity layer with many coarse grain components. As a result, as in this report, it was assumed that there is a low electrical resistivity region in the deep part, and that the sand boiling occurred where the low electrical resistivity layer on the surface layer was thin.