| 講演要旨(和文) | | 福岡県西方沖地震で大きな被害を受けた玄界島の宅地地盤において、石積み擁壁の強度を推定することを目的として、壁面で地震探査を行った。玄界島では地震により多くの石積み擁壁が被害を受けたが、このような擁壁の内部構造や強度を表面から非破壊で検査することは現状では困難である。そこで地震探査により擁壁のS波速度や厚さを推定することを試みた。受振器としては固有周波数28Hzの速度型地震計12個を1m間隔で壁面に人力で圧着し、起振はカケヤで壁面を打撃することにより行った。測定の結果、連続性の良い明瞭な波群が得られ、周波数とともに位相速度が高くなる明瞭な分散曲線が得られた。推定したS波速度構造は、概ね擁壁の被害状況を反映している。手法の妥当性を検証するために三次元差分法により、不均質な擁壁を伝わる理論的な波動場を計算したところ、概ね観測波形と一致する結果が得られた。 |
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| | 講演要旨(英文) | | The 2005 Fukuoka-Ken Seiho-Oki Earthquake with magnitude 7 caused severe damages on the masonry retaining walls of residential areas in the Genkai Island. It is difficult to evaluate the structure and earthquake resistance of the masonry retaining walls from wall surface non-destructively. A seismic investigation has been performed in the Genkai Island in order to evaluate the internal structure of masonry retaining walls. P-SV waveforms were observed and its dispersion characteristics were studied to estimate the avereged stiffness of the retaining walls. A sledge hammer was used as source and 28Hz geophones were used as receivers. Continuous waveform data were observed and the multi-channel analysis of surface-waves provided clear dispersion curves in which velocity increases with frequency. It seems that S-wave velocity models obtained through the dispersion analysis reflect retaining wall structures. In order to study wave propagation in heterogeneous masonry retaining walls, 3D finite-difference modeling was carried out. Calculated waveforms and dispersion curves agreed with observed ones very well. |
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