STABILIZATION OF TUNNEL FACE WITH CURVED TUNNEL FACE

Full-face tunnel excavation has been increasingly employed for SEM (sequential excavated method) tunneling by the virtue of enhanced capacity of roadheaders as well as the ground control effect of early ring closure. As the stability of the tunnel face is essential to full-face tunnel excavation, the tunnel stabilizing method utilizing curved tunnel faces, which would naturally form as part of the tunnel excavation sequences, can be considered effective. This paper addresses an investigation into the characteristics of the shape of curved tunnel face employing numerical models, and the stabilizing effect of tunnel face reinforcing methods, such as shotcrete on tunnel face, using physical models. Further, the constructability and stability of curved tunnel face were verified through trial excavations at an actual tunneling site. As a result it is confirmed that curved tunnel faces are advantageous and the stability of the tunnel face can be improved by a simple reinforcing method such as shotcrete on tunnel face. The trial excavations undertaken have proved the favorable constructability and stability of curved tunnel face. In addition, a conceptual approach to selection of the shape of curve tunnel face and its stabilization behavior is suggested together with a concept of tunnel face stabilizing method proposed. 掘削機械の大型化および支保構造の早期閉合による変位抑制効果から全断面掘削の施工が増大している．全断面掘削では切羽の安定が重要であり，自然形成的な曲面切羽を用いる安定化工法は有効と考えられる．本論文では，曲面切羽の形状の違いによる安定効果を数値解析により，鏡吹付けコンクリート等の鏡面補強工の支保効果を模型実験により検証した．また，実トンネルの試験施工で曲面切羽の安定性，施工性の検証を行った．その結果，曲面切羽形状の優位性および鏡吹付けコンクリート等による簡易な補強で切羽安定性が大きく向上することが確認された．試験施工からは曲面切羽の安定性，施工性の良さが確認された．また，掘削目標曲面形状および曲面切羽の安定化挙動を示し，切羽安定化工法の考え方も提案する．