Estimation of regional stress by FEM for a heterogeneous rock mass with a large fault |
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| Authors: | K. Matsuki S. Nakama T. Sato |
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| Affiliation: | 1. Department of Environmental Studies, Graduate School of Environmental Studies, Tohoku University, 6-6-20 Aramaki-aza-Aoba, Sendai 980-8579, Japan;2. Japan Atomic Energy Agency, 1-64 Yamanouchi, Akeyo, Mizunami 509-6132, Japan;1. College of Petroleum Engineering, Southwest Petroleum University, China;2. Massachusetts Institute of Technology, USA;3. College of Petroleum Engineering, China University of Petroleum, Huadong, 266580, China;4. Chuanqing Drilling Engineering Company, CNPC, China;1. School of Civil Engineering, Surveying and Construction, University of KwaZulu Natal, Durban, South Africa;2. Department of Civil Engineering, Indian Institute of Technology, Kanpur 208 016, India;1. Department of Civil Engineering, University of Toronto, 35 St. George Street, M5S 1A4 Toronto, ON, Canada;2. Geomechanica Inc., 90 Adelaide St. W., Suite 300, M5H 3V9 Toronto, ON, Canada;3. National Cooperative for the Disposal of Radioactive Waste (NAGRA), Hardstrasse 73, 5430 Wettingen, Switzerland;1. GFZ German Research Centre for Geosciences, Telegrafenberg, Potsdam, 14473, Germany;2. Department of Earth and Planetary Science, University of California, Berkeley, CA 94720, USA;3. CERMES – Laboratoire Navier Ecole des Ponts Paros Teche, 6-8 Av. Blaise Pascal, Cite Descartes Champs sur Marne, 77455, Marne la Vallee Cedex 2, France;1. State Key Laboratory of Geomechanics and Geotechnical Engineering, Institute of Rock and Soil Mechanics, Chinese Academy of Sciences, Wuhan, Hubei 430071, PR China;2. Key Laboratory of Safety for Geotechnical and Structural Engineering of Hubei Province, School of Civil Engineering, Wuhan University, Wuhan, Hubei 430072, PR China;3. University of Chinese Academy of Sciences, Beijing 100049, PR China;4. State Key Laboratory of Shield Machine and Boring Technology, Zhengzhou, Henan 450001, PR China |
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| Abstract: | Defining 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 the in situ stress, we propose a method for determining regional stress from limited stress data by using a 3D finite element method (FEM). First, 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 poor modeling and incomplete stress data. 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 can be used to estimate appropriate values of the normal and shear stiffnesses of the fault when the fault is homogeneous, 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. Next, the method was applied to the Tono area, Japan, where a large fault with a complex geometry, called the Tsukiyoshi fault, exists. The results obtained under the assumption that the Tsukiyoshi fault does not slide showed that (1) the stress distribution was estimated reasonably well only for a narrow region that contained the boreholes at which the stress used in the inverse analysis was measured, (2) the stress in the area shows a large scatter and a non-linear trend with depth, which is mainly caused by the Tsukiyoshi fault, and (3) when a fault is heterogeneous, comprehensive examination for the states of the stress and displacements on the fault is needed to obtain a reasonable estimation for the regional stress. |
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