巨礫が点在する崖錐を注入式フォアポーリング により突破：熊野尾鷲道路　大吹トンネル新鹿工区ー

摘要

The ground near tunnel entrance on the Owase side of the Kumano-Owase Road Obuki Tunnel is loose unconsolidated talus deposit that contains boulders with a diameter of one meter or more. It is difficult to predict face stability and ground behaviour based on existing geological information, because we have little experience with such an unusual ground condition. For this reason, prior to construction, we evaluated face stability at the time of excavation and select measures appropriate for ground characteristics after a detailed investigation of geological characteristics at the tunnel entrance. Furthermore, we measured and evaluated the stress of steel support and shotcrete lining and ground displacement along tunnel during construction to confirm the validity of support and measures. This report gives details of how the tunnel was constructed safely and economically under particular ground conditions.%熊野尾鷲道路大吹トンネルの尾鷲側坑口部は，ルーズな未固結崖錐層中に直径1m以上の巨礫が点在する過去の事例が少ない地山条件であり，既知の地質情報のみでは，トンネル掘削時の切羽安定や地山挙動の予測が困難であった.そのため，施工に先立ち，坑口部の地質特性を詳細に調査したうえで，トンネル掘削時の切羽の安定性を評価し，地山性状に応じた適切な対策ェを選定した.さらに，施工時に支保ェの応力やトンネル周辺地山の変位などを計測し，評価す ることで，支保ェゃ対策ェの妥当性を確認した.rn本稿では，このような特殊な地山条件のもとで，坑口部を安全かつ経済的に施工した経緯について報告する.