| 講演要旨(和文) | | 平成26年7月9日、台風8号の接近で活発化した梅雨前線の豪雨により、長野県南木曽町梨子沢で土石流災害が発生した。土石流は上流部にあった梨子沢堰堤を直撃して一部を消失させ、残った堤体本体には亀裂や施工継ぎ目で段差を生じさせた。本研究は土石流によって砂防堰堤がどのように破壊されたのかを考察するため、GPRを用いて堤体内部の亀裂分布を調査したものである。測定では中心周波数300/800MHzのインパルスレーダを天端より吊り下げて、壁面の約10m×13mの範囲を横断方向に0.2m間隔で、上下方向に0.01m間隔スキャンした。その結果、亀裂は低角に傾斜し、壁面から深さ0.5m程度までの表層に分布していることがわかった。また多点撮影したデジタルカメラの画像解析から、堤体上部は約13cm全面に押し出されていることが推定された。この押し出しに追随した堤体下部の壁面表層が広範囲に剥離した状況が考えられた。 |
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| | 講演要旨(英文) | | After the seasonal rain front which had become more active by typhoon number 8 approaching brought the localized heavily rain at Nagiso town, Nagano prefecture in July 9, 2014, the disaster of debris flow occurred at Nashizawa valley. When the debris flowed along Nashizawa valley, Nashizawa Sabo dam where located in upstream area of the valley received it and lost a upper concrete block of dam body.The remained dam body was pushed and was partially displaced to the front, and several open cracks appeared on the face of the dam body. The authors surveyed the internal fracture in the concrete body of the Sabo dam by GPR to understand destroyed process of the Sabo dam. We scanned about the area of 10 m by 13m on the front face of the Sabo dam by suspending dual antennas of central frequency 300/800MHz from the crest of the dam. As a result of GPR measurement, we found that the cracks inclined with low angle to the wall surface of the dam and distributed near surface to the depth of about 0.8m. We also estimated the deformation of the front face by analyzing digital photographs. The result showed that upper block of remained Sabo dam body was pushed about 13cm to the front. We considered that the detected reflections were lower boundary of separated thin concrete block by following the block which was pushed to the front. |
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