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- Bäckström, Ann, et al.
(author)
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Numerical modelling of uniaxial compressive failure of granite with and without saline porewater
- 2008
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In: International Journal of Rock Mechanics And Mining Sciences. - : Elsevier BV. - 1365-1609 .- 1873-4545. ; 45:7, s. 1126-1142
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Journal article (peer-reviewed)abstract
- It is important for rock engineering design to be able to validate numerical simulations, i.e. to check that they adequately represent the rock reality. In this paper, the capability and validity of four numerical models is assessed through the simulation of an apparently simple case: the complete process of microstructural breakdown during the uniaxial compressive failure of intact crystalline rock. In addition to comparing the capabilities of the four models, the results generated by each model were compared with the experimentally determined complete stress-strain curves for the Swedish Avro granite for different porewater conditions. In this way, it has been possible to audit the models' adequacy for this particular simulation task. It was found that although the models had common features, they were each idiosyncratically different and required considerable expertise to match the actual stress-strain curves (which did not monotonically increase in axial strain)-indicating that, for more complex simulations, both adequate modelling and appropriate validation are not going to be an easy task. The work was conducted within the framework of the international 2004-2007 DEmonstration of COupled models and their VALidation against EXperiments with emphasis on Thermo Hydro Mechanic and Chemical aspects (DECOVALEX-THMC) phase on coupled modelling extended to include chemical effects and with application to the excavation damaged zone (EDZ) in crystalline rock.
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- Koyama, Tomofumi, et al.
(author)
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Numerical simulations for the effects of normal loading on particle transport in rock fractures during shear
- 2008
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In: International Journal of Rock Mechanics And Mining Sciences. - : Elsevier BV. - 1365-1609 .- 1873-4545. ; 45:8, s. 1403-1419
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Journal article (peer-reviewed)abstract
- Fluid flow and tracer transport in a single rock fracture during shear is investigated using the finite element method (FEM) and streamline particle tracking, considering evolutions of aperture and transmissivity with shear displacement histories under different normal stresses, based on laboratory tests. The distributions of fracture aperture and its evolution during shear were calculated from the initial aperture fields, based on the laser-scanned surface roughness of feature replicas of rock fracture specimens, and shear dilations measured during the coupled shear-flow tests in laboratory. The coupled shear-flow tests were performed under two levels of constant normal loading (CNL). A special algorithm for treating the contact areas as zero-aperture elements was used to produce more accurate flow field simulations using FEM. The simulation results agreed well with the flow rate data obtained from the laboratory tests, showing complex histories of fracture aperture and tortuous flow channels with changing normal stresses and increasing shear displacements for the flow parallel with the shear direction. A greater increase was observed for flow in the direction perpendicular to the shear direction, due to the significant flow channels created by the shearing process. From the obtained flow velocity fields, particle transport was predicted using a streamline particle tracking method with the flow velocity fields (vectors) taken from the flow simulations, yielding particle travel times, breakthrough curves, and the Peclet number, Pe. The transport behavior in the fracture is also anisotropic, and advective transport is greater in the direction parallel with the shear direction. The effect of normal stress on the particle transport is significant, and dispersion becomes larger with increasing normal stress.
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- Li, Bo, et al.
(author)
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Experimental study of the hydro-mechanical behavior of rock joints using a parallel-plate model containing contact areas and artificial fractures
- 2008
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In: International Journal of Rock Mechanics And Mining Sciences. - : Elsevier BV. - 1365-1609 .- 1873-4545. ; 45:3, s. 362-375
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Journal article (peer-reviewed)abstract
- In recent years, geological disposal of radioactive wastes is considered to be the most promising option, which requires the understanding of the coupled mechanical, hydraulic and thermal properties of the host rock masses and rock fractures. The hydro-mechanical behavior and properties of rock fractures are usually determined by laboratory experiments on fracture specimens that serve as the basic building block of the constitutive models of fractured rock masses. Laboratory testing of rock fractures involve a number of technical issues that may have significant impacts on the reliability and applicability of the testing results, chief among them are the quantitative estimation of the evolutions of hydraulic transmissivity fields of fractures during shear under different normal constraint conditions, and the sealing techniques when fluid flow during shear is involved. In this study, a new shear-flow testing apparatus with specially designed fluid sealing techniques for rock fractures were developed, under constant normal load (CNL) or constant normal stiffness (CNS) constraint. The topographical data of all fracture specimens were measured before testing to constitute the geometrical models for simulating the change of mechanical aperture distributions during shearing. A number of shear-flow coupling tests were carried out on three kinds of rock fracture specimens to evaluate the influence of morphological properties of rock fractures on their hydro-mechanical behaviour. Some empirical relations were proposed to evaluate the effects of contact area and surface roughness on the behavior of fluid flow through rock fractures.
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