1998 Fiscal Year Final Research Report Summary
A THEORETICAL AND EXPERIMENTAL STUDY FOR ESTIMATING THREE-DIMENSIONAL IN-SITU STRESSES FROM CORE DISCING
| Project/Area Number |
08405066
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| Research Category |
Grant-in-Aid for Scientific Research (A)
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| Allocation Type | Single-year Grants |
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| Section | 一般 |
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| Research Field |
資源開発工学
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| Research Institution | TOHOKU UNIVERSITY |
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Principal Investigator |
MATSUKI Koji Dept.Geoscience and Technology, Tohoku Univ.professor, 大学院・工学研究科, 教授 (10108475)
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| Co-Investigator(Kenkyū-buntansha) |
OKUMURA Kiyohiko Dept.Geoscience and Technology, Tohoku Univ.research associate, 大学院・工学研究科, 助手 (40177184)
SAKAGUCHI Kiyotoshi Dept.Geoscience and Technology, Tohoku Univ.research associate, 大学院・工学研究科, 助手 (50261590)
KIYOHASHI Hiroshi Dept.Geoscience and Technology, Tohoku Univ.associate professor, 大学院・工学研究科, 助教授 (70005263)
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| Project Period (FY) |
1996 – 1998
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| Keywords | Core discing / Three-dimensional in-situ stresses / Triaxial loading system / Saddle shaped disc / Tensile principal stress analysis |
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| Research Abstract |
The direction and the magnitude of tensile principal stresses within and below a long HQ core stub were analyzed with a finite element method for 77 in-situ stress conditions. 26 stress conditions were identified to be those under which core discing is likely to occur. A criterion for core discing was then proposed by evaluating the maximum tensile principal stress which is necessary for the contour plane to be formed throughout a cross-section of the core. A detail analysis on the distributions of the direction of tensile principal stresses showed that almost planar surfaces might be formed in the central part of the end surfaces of a dics and that large difference between the maximum and intermediate principal stresses might produce a so-called saddle shaped periphery. Summarizing the results obtained by the analysis, a procedure for determining principal in-situ stress directions from the geometry of a disc was proposed, based upon the symmetry of the end surfaces, the normal direction in the central part of the end surfaces and the direction of the concave or the convex axes in the end surfaces.
To verify the methods for estimating three-dimensional in-situ stresses from core discing, described above, experiments on core discing were carried out for Shirakawa welded tuff and Kimachi sandstone by loading a block containing a long core with a triaxial loading system. The criterion for core discing proposed in this study approximately estimated the stresses at which core discing initiated for Shirakawa welded tuff. However, the stresses predicted by the criterion did not coincide with the experimental results for Kimachi sandstone, for which the core discing was accompanied by compressive failure at the borehole bottom. A saddle shaped dicing was not observed for these rocks even if two horizontal stresses were different.
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Research Products
(8 results)
