Delineation of Dead-End Structure of Thin Sand Layer by ERT and Cylinder Electrode CCR Survey
C. Konishi, Y. Yamashita, K. Takahashi, D. Kurata and A. Shinsei
Event name: 25th European Meeting of Environmental and Engineering Geophysics
Session: Geophysics for Geotechnics
Publication date: 11 September 2019
Info: Extended abstract, PDF ( 1.14Mb )
Price: € 20
2D ERT and cylinder electrode capacitively coupled resistivity (CCR) survey has been conducted to detect dead-end structure of a thin sand layer that may cause piping and a river levee collapse in the worst case. The survey lines were placed at an inland side of Tokoro river where a flood occurred by unprecedented heavy rainfall in 2016. We planted electrodes with 0.5 m spacing to increase the vertical resolution for ERT, and cylinder electrode, which is equivalent to 0.5 m dipole cable, was employed for the CCR survey. As a result, high resistivity thin layer was detected at 1 m depth, and dead-end structure was observed by 2D ERT and CCR survey. Soil samples were collected by auger drilling at several places around the observed dead-end point of the high resistivity layer and lateral variations of the soil were confirmed. It suggested the sand layer was terminated and the capability of ERT and the cylinder electrode CCR for delineating the thin sand layer was verified.