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- Koyama, Tomofumi, et al.
(författare)
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Numerical simulation of shear-induced flow anisotropy and scale-dependent aperture and transmissivity evolution of rock fracture replicas
- 2006
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Ingår i: International Journal of Rock Mechanics And Mining Sciences. - : Elsevier BV. - 1365-1609 .- 1873-4545. ; 43:1, s. 89-106
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Tidskriftsartikel (refereegranskat)abstract
- Fluid flow anisotropy in a single rock fracture during a shear process is an important issue in rock mechanics and is investigated in this paper using FEM modelling, considering evolutions of aperture and transmissivity with shear displacement history. The distributions of fracture aperture during shearing with large shear displacements were obtained by numerically manipulating relative translational movements between two digitalized surfaces of a rock fracture replica, with changing sample sizes. The scale dependence of the fluid behaviour and properties were also investigated using a fractal approach. The results show that the fracture aperture increases anisotropically during shear with a more pronounced increase in the direction perpendicular to the shear displacement, causing significant fluid flow channelling effect, as also observed by other researchers. This finding may have important impacts on the interpretation of the results of coupled hydro-mechanical experiments for measurements of hydraulic properties of rock fractures because the hydraulic properties are usually calculated from flow test results along the shear directions while ignoring the more significant anisotropic flow perpendicular to the shear direction. This finding indicates that the coupled stress-flow tests of rough rock fractures should be conducted in true three-dimensions if possible. Significant change in fracture aperture/ transmissivity in the out-of-plane direction should be properly evaluated if two-dimensional tests are conducted. Results obtained from numerical simulations also show that fluid flow through a single rough fracture changes with increasing sample size and shear displacements, indicating that representative hydro-mechanical properties of the fractures in the field can only be more reliably determined using samples of large enough sizes beyond the stationarity threshold and tested with larger shear displacements.
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- Koyama, Tomofumi, et al.
(författare)
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Tracer transport in a rough rock fracture during shear : a numerical study
- 2006
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Ingår i: Proc of the 2nd International Conference on Coupled T-H-M-C Processes in Geo-Systems: Fundamentals. ; , s. 575-580
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Konferensbidrag (refereegranskat)abstract
- The effects of translational shear on particle transport under coupled shear-flow testing conditions in a rough rock fracture were numerically investigated in this study. A pair of digitalized surfaces of a rough concrete fracture replica was numerically manipulated to simulate the translational shearing process without considering normal loading and asperity damage. From the evolutions of the aperture filed during shear, the evolutions of the fracture transmissivity field were determined. Undirectional and bi-directional fluid flow situations were considered, using Finite Element Method (FEM). The results show that translational shear makes rough fractures more permeable, producing a significant change in travel time of the particles. Translational shear yields a significant channelling effect in the direction perpendicular to the shear direction. Bi-directional flow patterns show clearly the shortcommings of the conventional laboratory shear-flow tests with unidirectional flow. These simulations provide a first step towards a better understanding of particle transport in rock fractures.
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