| 講演要旨(和文) | | 橋台設置工事が予定されていた河川堤防において，堤体内部物性構造の把握を目的とした統合物理探査を実施した．実施手法は，縦断方向の統合物理探査，横断方向の比抵抗トモグラフィ探査である．また開削後には開削面観察に加え，比抵抗マッピングおよび小間隔表面波探査を実施した．加えて表面波探査データの多相解析によって，明瞭な浅部断面構造を得ることができた．これらの開削前調査結果を，橋台設置時の杭施工実績および開削面における探査結果と対比したところ，きわめて調和的であった．このことは表面波探査データの多相解によって表層15m程度までのS波速度構造だけでなく，深さ50m程度までの堆積構造をも復元可能であることがわかった． |
|
|
| | 講演要旨(英文) | | Integrated geophysical surveying was conducted on a levee system part of which was to be excavated for constructing a bridge abutment. The integrated geophysics comprised DC resistivity, OhmMapper resistivity, and high-resolution surface wave surveys along a short line about 200 m set on the levee crest. Resistivity tomography measurement across the levee body was also applied. We conducted resistivity mapping and supplemental short spacing surface wave measurements on the surface after excavation of the levee body. The integrated geophysical surveys clearly delineated a small anomaly featured by high resistivity and high S-wave velocity just at the portion where the levee intersects an old meandering channel. A migrated depth section, obtained from the surface wave data through ordinary S-wave seismic reflection processing, reconstructed clean near-surface structure down to 40 m. The structure was characterized as a steeply dipping unconformity. The estimated depths of the unconformity were well concordant with array piling work results. |
|
|
|
| |
|