APPLICABLE RANGE OF INCLINATION MONITORING METHOD FOR PREDICTION OF GEOTECHNICAL CONDITION AHEAD OF TUNNEL FACE AND ITS QUANTITATIVE EVALUATION

山岳トンネルの安全かつ経済的な施工には，切羽前方の地山状況を精度よく予測して，必要に応じて予防保全的な対策工を講じる事が重要である．これまでに筆者らは，日常の施工管理の一環として，簡易に実施できるトンネル天端部の傾斜計測によって，切羽前方地山の硬軟変化を予測する手法を考案し，数値解析や現場計測試験で妥当性と有効性を確認してきた．本論文では，提案手法によって切羽前方地山予測を実現できる条件を明確化する目的で，土被りや地山剛性をパラメータとした感度解析を実施した．また，傾斜計測による地山状況予測結果を，変形余裕量の設定や補助工法の検討に対して実務的に活用することを目指して，傾斜角度から天端沈下量を定量的に推定する方法を検討し，現場実装試験の事後評価で有効性を確認した．
Safe and cost-effective excavation of mountain tunnels requires accurate prediction of geotechnical condition ahead of the tunnel face and preventive auxiliary methods or appropriate support members should be adopted correspondingly. Authors have so far developed a method to predict the change in ground stiffness ahead of the tunnel face by means of inclination monitoring which can be applied without any hindrance to the construction. Applicability and validity of the method have been verified through numerical simulation and field measurement tests. This study performs parametric numerical simulations in which ground stiffness at the face under excavation and ahead of the face, and tunnel overburden are considered as variables in order to clarify the geotechnical condition required for the application of the proposed prediction method. The study also discusses a quantitative estimation method for the tunnel crown settlement by measured inclination. This leads to further effective use of ground prediction results in which allowable deformation volume and appropriate auxiliary methods required can be determined beforehand. Effectiveness of the estimation method is investigated through the post-evaluation of field measurement data.