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Title: Short- and Long-Term Observations of Fracture Permeability in Granite by Flow-Through Tests and Comparative Observation by X-Ray CT
Authors: Song, Chenlu
Nakashima, Shinichiro
Kido, Ryunosuke  kyouindb  KAKEN_id  orcid (unconfirmed)
Yasuhara, Hideaki
Kishida, Kiyoshi  kyouindb  KAKEN_id  orcid (unconfirmed)
Author's alias: 宋, 忱潞
木戸, 隆之祐
安原, 英明
岸田, 潔
Keywords: Permeability
Short- and long-term tests
X-ray CT observation
Contact-area ratio and aperture distribution
Issue Date: Sep-2021
Publisher: American Society of Civil Engineers (ASCE)
Journal title: International Journal of Geomechanics
Volume: 21
Issue: 9
Thesis number: 04021151
Abstract: Having a grasp of the variation in the fracture contact area is a kernel in the understanding of the permeability evolution of fractured rocks. However, the number of studies that focus on measuring the long-term variation in the fracture contact area under different conditions is insufficient. In this study, a series of short- and long-term permeability tests under coupled conditions is performed to check the performance of permeability. The results reveal that the permeability measured in the short-term tests shows reversible behavior and a dependence on the applied confining pressures and temperature. In contrast, the permeability in the long-term tests displays irreversible behavior and an irregular change under the constant confining pressure. In order to verify the evolution of permeability, microfocus X-ray computed tomography (CT) is developed to observe the changes in the internal fracture structure under the same conditions as those in long-term permeability tests by assembling a triaxial cell with heating capability. The fracture aperture and the fracture contact-area ratio are calculated by a CT image analysis technique. The image analysis results show that the estimated aperture is seen to decrease with an increase in the confining pressure and to also decrease with time under a constant confining pressure. Moreover, the increase in the fracture contact area under the constant confining pressure observed by X-ray CT is confirmed. This also corresponds to a decrease in permeability in long-term tests. The hydraulic aperture calculated from the permeability tests and that evaluated from the CT observation have a similar decreasing trend. Therefore, the CT observation can better capture the evolution of the internal fracture contact area. These experiments underscore the importance of mechanical compaction and/or mineral dissolution at contacts in determining the rates and the magnitude of permeability evolution within rock fractures.
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This is not the published version. Please cite only the published version. この論文は出版社版でありません。引用の際には出版社版をご確認ご利用ください。
DOI(Published Version): 10.1061/(ASCE)GM.1943-5622.0002114
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