Estimation of rock mass stress state based on convergence measurement during gallery excavation

坑道掘削時の内空変位測定結果に基づく地殻応力状態の推定

青柳 和平  ; 名合 牧人*; 亀村 勝美*; 菅原 健太郎*

Aoyagi, Kazuhei; Nago, Makito*; Kamemura, Katsumi*; Sugawara, Kentaro*

Estimates of rock mass stress state and the mechanical characteristics of rock mass are important in the design of deep underground structures such as high-level radioactive waste disposal repositories. Stress measurements are conducted in boreholes to provide estimates of stress state. However, measurement results can vary highly as a result of rock mass heterogeneity, which causes difficulty in stress state evaluation. This study establishes a practical and effective method for estimating in situ stress based on the convergence measurement results obtained during gallery construction of the Horonobe Underground Research Laboratory (URL) project. The convergence was measured in various directions of the URL loop gallery to allow determination of the stress state over a large area. A back-analysis method was developed using the convergence measured during gallery excavation at 350 m depth. This method was applied to estimate the stress state corresponding to the rock mass behavior around the URL. The analysis results show good agreement with the in situ stress state reported in previous studies and confirm the applicability of the proposed method.