ノンコァ削孔検層を活用した補助工法要否の判定と小土かぶり部の掘削:九州横断自動車道田代第ニトンネル

摘要

The Tashiro 2nd Tunnel is a two-lane road tunnel of 531m in length located between Kashima Junction and Yabe are required in excavation of weak Mifune Group, we constructed criteria using non-core drilling logging and checked their adaptability. In addition, in ground with small overburden (minimum cover of approx. 3m), we investigated in advance using core boring and three-dimensional analysis, reviewed analysis based on measurement results at the time of excavation and stabilized the ground surface. We ensured stability of tunnel and surface ground in places where there was concern about large ground surface settlement by controlling deformation of tunnel through reinforcing tunnel supports and temporary closing of tunnel invert. This report contains information on the adaptability of standards to determine auxiliary methods used in this construction and excavation results for tunneling under small overburden.%田代第二トンネルは，九州横断自動車道延岡線の嘉鳥JCT〜矢部IC間に位置する延長531mの2車線道路トンネルである.本トンネルでは，脆弱な御船層群の掘削において補助工法の要否を判定するためにノンコア削孔検層を活用した判定基準を構築し，その適用性を確認した.また最小土かぶりが約3mとなる小土かぶり区間では，事前にコアボーリングおよび3次元解析による検討を行い，掘削時には計測結果にもとづいて解析を修正し，地表面の安定を図った.一部，大きな地表面沈下が懸念された箇所では支保の補強および仮ィンバート閉合によって坑内変位を抑制しトンネルおよび地表地山の安定を確保した. 本稿では本トンネルで採用した補助工法の要否の判定基準の適用性と小土かぶり区間の掘削実績について報告する.