トンネル掘削発破を用いた切羽前方長距離探査法「T-BEP®」のスマート化と検証
山岳トンネル工事では施工上問題となる可能性のある破砕帯などの弱層に関する情報を事前に把握することが安全性や経済性の上で重要である。施工を妨げることなくトンネル工事計画の確実な長期見通しを可能とするために，掘削用発破を震源とする坑内反射法弾性波探査としてT-BEP（Taisei Blast Excavation Prospecting）を開発した．本手法の最大探査距離は350m以上で，従来法の2～3倍以上であった．しかし，準備と計測作業が煩雑であることや，安全性向上の余地があった．そこで受振器の設置方法の簡便化，配線の無線化，専用発破器による安全性向上等のスマート化による新型T-BEPを開発した．新型と旧型のT-BEPを同一切羽から実施する検証実験を行った．新型と旧型ともに最大探査距離は従来法の2～3倍以上を維持した上で，新型T-BEPは準備・計測作業の大幅な改善と安全性向上が確認された．
キーワード：山岳トンネル，坑内反射法弾性波探査，切羽前方探査，T-BEP
＊１ 技術センター 社会基盤技術研究部 地盤研究室
Smartification and Accuracy Verification of Long-distance Ahead-of-face Survey Method "T-BEP®" Using Tunnel Excavation Blasting as Seismic Source
In mountain tunneling, it is important from the point of construction safety and effectiveness to obtain information on the weak zones such as fracture zones ahead of face, which may pose problems during construction. The authors have developed a tunnel seismic refection survey method known as Taisei Blast Excavation Prospecting (T-BEP) to provide a long-term outlook for tunnel work without disturbing excavation. The maximum surveyable distance of this method is beyond 350m, two to three times greater than the conventional methods. However, complicated works were necessary in the preparation and measurement processes, and there were safety concerns. Therefore, we have developed a new T-BEP, smartening it up by simplifying the installation of receiver and wirelessing the connectivity, and by enhancing safety through development of dedicated blasting device. Comparative surveys were conducted using the new and old T-BEPs from the same face location in a tunnel under construction. The survey results were compared in terms of the ground conditions after excavation. It was found that the maximum surveyable distance of both new and old T-BEPs were beyond 350m, and also that the new T-BEP brought significant improvements and enhanced safety in the preparation and measurement operations.
Keywords: mountain tunnel, tunnel seismic reflection survey, survey ahead of the face, T-BEP
*1 Geotechnical Research Section, Infrastructure Technology Research Department, Taisei Advanced Center of Technology