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発表 Ground truthing for the verification of an integrated geophysical surveying for the safety assessment of levee systems

作成年度 2012 年度
論文名 Ground truthing for the verification of an integrated geophysical surveying for the safety assessment of levee systems
論文名(和訳)
論文副題
発表会 The 26th Annual Symposium on the Application of Geophysics for Engineering and Environmental Problems (SAGEEP)
誌名 Proceedings of the Annual Symposium on the Application of Geophysics to Engineering and Environmental Problems (SAGEEP)
巻・号・回 26(2013)
発表年月日 2013/03/01
所属研究室/機関名 著者名(英名)
Geology and Geotechnical Engineering Research GroupT. Inazaki
抄録
We have proposed a recommended integrated geophysical technique to assess the vulnerability of earthen levees toward flooding and earthquake. The geophysical method mainly consists of high-resolution surface wave surveying using Land Streamer (LSSW), capacitively coupled resistivity (CCR) measurement using OhmMapper, and additional multi-frequency electromagnetic (EM) survey. We have also demonstrated the usefulness of crossplot analysis for the classification of physical properties of levee systems. Recently, the technique has been widely applied to the levees damaged by the 2011 East Japan Earthquake. However, complaints such as decrease in resolution with depths and uncertainties in interpretation of the technique have arisen from river engineers in Japan. Then, it has been urgently requested to the geophysicists to make clear what anomaly the geophysical methods could delineate and how heterogeneous levee systems are. Ground truthing is one of the best ways to verify the performance of the integrated geophysical surveying applied to the levee systems. We then conducted detailed geophysical surveys and field measurements at the sites where levees were to be excavated before and after the excavation. For example, small but dense DC resistivity and LSSW survey along a levee had delineated a high resistivity and low Vs body at shallow depths and interpreted it as loose sand used to cover a culvert. We could directly identify the corresponding sand layer just at the interpreted locations after excavation. In another case, DC resistivity and S-wave tomography survey across a levee body successfully delineated layered structure in the levee. Excavation of the levee cropped out the internal stacked structure concordant with the survey interpretation. Supplemental CPT and SCPT measurements would be helpful to obtain 1D but detailed profile of resistivity, Vs in levee systems.
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