Estimation of regional stress by FEM for a heterogeneous rock mass with a large fault

大断層を含む不均一岩体の有限要素法による広域応力場の評価

松木 浩二*; 中間 茂雄 ; 佐藤 稔紀  

Matsuki, Koji*; Nakama, Shigeo; Sato, Toshinori

大規模断層を含む不均一岩体の広域応力場の評価法について、三次元有限要素法を用い、二つの研究を実施した。一つ目の研究として、小規模モデルを対象とした基礎的研究として、断層が部分的に滑る場合の広域応力場評価とともに、断層が滑っていない場合について、評価精度に及ぼす断層剛性の設定値,地圧データの与え方,断層滑りの影響等、評価手法について検討した結果を述べる。二つ目の研究として、広領域の東濃地区に月吉断層が存在する場合を対象として、断層が滑らないと仮定した場合の広域応力場評価に関する研究を行い、現在までに測定された地区データを用いて広域応力場を評価し、小規模モデルに関する研究で得られた知見を基礎としてその妥当性について検討し、東濃地区の応力分布の傾向を論じた。

This paper consists of two parts. In Part I, we propose a method for determining regional stress from limited stress data by using a 3D finite element method (FEM) in which we define regional stress for a heterogeneous rock mass composed of different rock bodies and a large fault as a displacement boundary condition that is consistent with the mean trend of in situ stress. This method was applied to a small-scale heterogeneous model with a large planar fault that penetrates the region to clarify the estimation accuracy and the effects of incorrect stiffness of the fault, incomplete stress data, and the assumption that the fault shows partial, but not complete, sliding. The results showed that (1) the method proposed in this study can accurately estimate the stress distribution in the region under consideration except at the bottom when the sliding area of the fault is small, (2) the reproducibility of the given stress indicates that the method can be used to estimate appropriate values of the normal and shear stiffnesses of the fault, and (3) both incomplete stress data and the assumption that the fault does not slide decrease the accuracy of stress estimation while the given stresses are approximately reproduced. In Part II, this method is applied to the Tono area, in Japan.