| 講演要旨(和文) | | 非破壊の堤防調査手法を確立するために、ルイジアナ州ニューオリンズの堤防沿いで物理探査を実施した。表面波探査、微動アレイ探査、牽引式電気探査を実施したが、このうち直線アレイによる2次元の微動アレイ探査の測定と解析についてまとめる。測定には12台のケーブルレスサイスモグラフと2Hzの速度型地震計を用いた。測定器はGPSを内蔵しておりケーブルを用いなくても時間を同期できる。測定器は5m間隔で直線上で配置し10分データを取得、後ろの4台を先頭に移動することを繰り返し、400〜1000mの測線を数時間で測定した。空間自己相関関数法を用いて解析した結果、全ての測線で明瞭な分散曲線が得られた。最低および最高周波数は測線によってそれぞれ1〜2Hzおよび9〜30Hzである。最小二乗法を用いた逆解析により深度40〜60mまでの堤防沿いのS波速度断面が得られ、その結果は既存のボーリングや室内試験結果と整合した。 |
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| | 講演要旨(英文) | | To develop non-invasive methods for levee inspection, geophysical investigations were carried out at three sites along levees in New Orleans. The sites sustained damage from Hurricane Katrina in 2005 and have since been rebuilt. The geophysical methods include active and passive surface wave methods, and capacitively coupled resistivity. This paper mainly summarizes the acquisition and analysis of 2D passive surface wave data. Twelve cableless seismic data acquisition units with 2 Hz vertical component geophones were used to record data. Each unit includes a GPS receiver so that all units can be synchronized over any distance without cables. Data acquisition used linear arrays with a geophone spacing of 5m. Four geophones were moved forward every 10 minutes along 450 ~ 1,100 m length lines. Data acquisition took several hours for each line. Recorded ambient noise was processed using spatial autocorrelation and clear dispersion curves were obtained at all sites. Minimum and maximum frequencies ranged from 1 to 2 Hz and from 9 to 30 Hz respectively depending on the site. Non-linear inversion yielded 2D cross sections along the levees penetrating to a depth of 40 ~ 60 m. Resultant S-wave velocity models are generally consistent with existing drilling logs and laboratory tests. |
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