| 講演要旨(和文) | | 路床中に巨礫が混入し，工事が中断した道路盛土の建設現場において，巨礫の埋没位置を把握するため，ネットワーク型RTK-GNSSと連動する地中レーダを用いて稠密探査を実施した．実際に回収された巨礫を埋設して検出実験を行い，路床材と巨礫の誘電率に差が生じやすい降雨後に探査することの有効性を確認した．実験後，直ちに約12,000m2に対して測線間隔約30cmで探査を開始した．受信波形に現れた礫上面と下面の反射波ペアから巨礫の特徴を分析して抽出基準を作成し，巨礫の可能性がある177箇所を抽出した．重複箇所等を整理し，148箇所を巨礫埋没位置としてマーキングした．掘削した結果，146箇所で巨礫を確認し，路床中から除去することに成功した．調査は検出実験から巨礫の除去まで実質わずか6.5日で完了することができた． |
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| | 講演要旨(英文) | | We conducted a highly dense survey by GPR system interfaced with a network typed RTK-GNSS to detect buried boulders in roadbeds layer of an embankment under construction. Firstly we buried boulders again, which actually were collected from roadbeds, and carried out experiments to detect the boulders. We confirmed the effectiveness of the detection after rain fall. The condition made a large permittivity difference between the boulders and the roadbeds. After the experiments, we immediately started investigating the area of about 12,000 m2 with survey lines of about 0.3m interval. Although total length of survey lines reached to about 43.4km, it took only 1.5days using two GPR systems. We defined a criterion to discriminate the anomalies caused by buried boulders from others. It based on a pair of GPR diffraction patterns which reflected at the top and bottom of boulders. We extracted 177 anomalies as possible boulder responses. We then conducted the secondary survey immediately to precisely locate the anomalies. Since some anomalies were detected multiple times because of dense survey lines, we finally identified 148 anomalies and marked the locations in the secondary survey. The located points were immediately dug out with a backhoe to confirm whether boulders had been buried or not. As a result, nonstandard sized boulders for embankment materials were excavated out of 146 anomaly points. Owing to the high effectiveness GPR survey within a total of 6.5 days from the primary survey to the excavation of identified boulders, we successfully contributed to minimize the delay in embankment works of the highway under construction. |
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