| 講演要旨(和文) | | 近年，都市部でトンネル等が建設されることが多くなってきた．都市部では未固結地盤や土丹層が浅い深度から出現する場合が多く，施工時に出水による坑内事故や土丹層中の介在砂層の流出に起因する地上構造物への影響が懸念される．そのため，施工を行う場合，介在砂層を二次元あるいは三次元で把握し，介在砂層からの湧水や砂の流出対策を行う必要がある．介在砂層は層厚が薄く，水平方向への連続性が乏しいことが多い．介在砂層を二次元あるいは三次元で把握するにはボーリングによる方法が確実ではあるが，経済性を考慮すると物理探査による方法が有利と考えられる．今回行った実験は，比抵抗トモグラフィで介在砂層を検出できるか，また砂層に薬液を注入して改良した場合に改良範囲を評価できるかということを目的に行った．その結果，三次元トモグラフィで精度よく砂層を検出し薬液による改良範囲を評価することができた． |
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| | 講演要旨(英文) | | The number of tunnel projects in urban areas has recently increased. In such projects, it is important to detect weak sand layers lying between soft rocks such as mudstones, and improve its strength and permeability by grouting to minimize the risks of tunnel collapses, water inflow into tunnels and ground settlement etc. The authors expect that 3D resistivity tomography is a useful geophysical investigation, and conducted a series of laboratory experiments to verify the detection of thin sand layer lying between mudstones by 3D resistivity tomography. Furthermore, the sand layers were grouted by chemical grout and cement grout, 3D resistivity tomography was carried out again to evaluate the grouting effect. As a result, first, the sand layers were detected as high resistivity area by 3D resistivity tomography. Secondly, it was shown that the resistivity of grouted area by chemical grout decreased and the resistivity of the sand layer grouted by cement grout increased. |
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