| Project/Area Number |
15360472
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| Research Category |
Grant-in-Aid for Scientific Research (B)
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| Allocation Type | Single-year Grants |
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| Section | 一般 |
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| Research Field |
Earth system and resources enginnering
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| Research Institution | Tohoku University |
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Principal Investigator |
TSUCHIYA Noriyoshi Tohoku University, Graduate School of Environmental Studies, Professor, 大学院・環境科学研究科, 教授 (40207410)
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| Co-Investigator(Kenkyū-buntansha) |
HIRANO Nobuo Tohoku University, Graduate School of Environmental Studies, Research associate, 大学院・環境科学研究科, 助手 (80344688)
NEMOTO Katsumi Tohoku University, Graduate School of Science, COE fellow, 大学院・理学研究科, COEフェロー (20396427)
GREGORY BIGNALL 東北大学, 大学院・工学研究科, 助手 (70333854)
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| Project Period (FY) |
2003 – 2005
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| Project Status |
Completed (Fiscal Year 2005)
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| Budget Amount *help |
¥13,600,000 (Direct Cost: ¥13,600,000)
Fiscal Year 2005: ¥2,900,000 (Direct Cost: ¥2,900,000)
Fiscal Year 2004: ¥4,500,000 (Direct Cost: ¥4,500,000)
Fiscal Year 2003: ¥6,200,000 (Direct Cost: ¥6,200,000)
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| Keywords | Fractures / Fluid flow / Hydrothermal flow / Channeling / Fracture aperture distribution / き裂構造 / 弾性波伝播速度 / 巨視き裂 / 微視き裂 / 鉱物脈 / 間隙幅 / フラクタルモデル / 花崗岩体 / 岩石き裂構造 / き裂異方性 |
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| Research Abstract |
1. Characterization of fractures in granitic rock mass on the basis of field observation
Based on geological field survey on granitoids distributed in the Chubu Ryoke Belt, orientation and occurrence of macroscopic (outcrop scale) fractures were analyzed to characterize the anisotropic fracture network system in the study area. Variation of P-wave velocity was measured to identify preferred orientation of weak planes developed in the granitic rocks. In northeast part of the Inagawa granite, parallelepiped block structure composed from fractures with three preferred orientation was observed. The structure is inferred to be derived from tensile stress field in the granitic body. On the contrary, in southwest part of the Inagawa granite and the old Ryoke granitic rocks, complex sheared fractures were dominant. Predominant orientations of those macroscopic fractures were close to the directions of major and representative active fault systems of the Chubu Ryoke area such as the Median Tecto
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nic Line (NE -SW strike) and the Atera fault (NW-SE strike). P-wave velocity measurement revealed that anisotropy of the P-wave velocity was closely related to the distribution of parallelepiped fractures, however, shear fractures had no clear relation to variation of the P-wave velocity. We showed, in the case of highly stressed rock mass, better approximation on preferred orientations of fractures is likely to be achieved with consideration for occurrence of major faults and tectonic stress regime distributed in the area.
2. Characterization of aperture distribution and flow paths of fractures
We attempted to reveal a relationship between fracture aperture and fluid flow in a tensile fracture by combining laboratory experiments and flow simulations in order to investigate flow properties in a tensile fracture up to 100 MPa and a variation of the flow properties associated with shear offset applied to the fracture. Our results showed 1) permeability in a tensile fracture rapidly decreased with an increase in normal stress, 2) the fracture permeability showed almost constant value at normal stress more than 40-50 MPa, 3) channeling in flow paths, which means specific area of the fracture behaves as major flow paths, is yielded, 4) the channeling was elucidated at higher normal stress conditions. We also proposed a technique for evaluating flow properties of a fracture in combination with the flow experiments and the flow simulation with considering flow path distribution indicating a microscopic flow property in addition to fracture permeability indicating a macroscopic flow property. Less
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