Microstructures, percolation thresholds, and rock physical properties

Guéguen, Yves; Chélidzé, T.; Ravalec, M. Le

doi:10.1016/s0040-1951(97)00132-7

Cited by 91 publications

(54 citation statements)

References 37 publications

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“…For Oshima and Toki granites, fracture is reached for a q value slightly larger than 1. Note that such a value is expected from 3-D percolation models (GUE´GUEN et al, 1997). Indeed, there are two different percolation thresholds for q: the first one is the permeability threshold at q $ 0:15 and the second one a fracture threshold at q $ 1.…”

Section: Elastic Stiffnesses Determinationmentioning

confidence: 78%

Velocity Measurements and Crack Density Determination During Wet Triaxial Experiments on Oshima and Toki Granites

Schubnel¹,

Nishizawa²,

Masuda³

et al. 2003

Pure appl. geophys.

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A set of experiments on four samples of Oshima Granite at 15, 40 and 60 MPa confining pressure have been performed in order to investigate the damage behavior of granite submitted to deviatoric stress. In addition an experiment on one sample of Toki Granite at 40 MPa confining pressure was performed, in order to compare and elucidate the structural effects. Using acoustic emission data, strain measurements and elastic wave velocities allow to define consistently a damage domain in the stress space. In this domain, microcracking develops. The microcracking process is, in a first stage, homogeneous and, close to failure, localized. Elastic wave velocities decrease in the damage domain and elastic anisotropy develops. Using KACHANOV's model (1993), elastic wave velocities have been inverted to derive the full second-order crack density tensor and characterize the fluid saturation state from the fourth-order crack density tensor. Crack density is strongly anisotropic and the total crack density close to failure slightly above one. The results indicate that the rock is saturated in agreement with the experimental conditions. The model is thus shown to be very appropriate to infer from elastic wave velocities a complete quantitative characterization of the damaged rock.

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Section: Elastic Stiffnesses Determinationmentioning

confidence: 78%

Velocity Measurements and Crack Density Determination During Wet Triaxial Experiments on Oshima and Toki Granites

Schubnel¹,

Nishizawa²,

Masuda³

et al. 2003

Pure appl. geophys.

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“…Within the context of fracture upscaling, it has been suggested that this behaviour can be identified with percolation, which is the transition from unconnected to connected fracture networks (Pozdniakov and Tsang, 2004;Barthélémy, 2008;Pouya and Ghabezloo, 2010). Unfortunately, there is no theoretical result justifying this conjecture, and many authors regard the self-consistent percolation estimates as spurious (Guéguen et al, 1997;Torquato, 2002). Numerical simulations are therefore valuable in order to assess the feasibility of the methods in this regime.…”

Section: The Symmetric Self-consistent Methodsmentioning

confidence: 99%

A 3D Computational Study of Effective Medium Methods Applied to Fractured Media

et al. 2013

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This work evaluates and improves upon existing effective medium methods for permeability upscaling in fractured media. Specifically, we are concerned with the asymmetric self-consistent, symmetric self-consistent and differential methods. In effective medium theory, inhomogeneity is modeled as ellipsoidal inclusions embedded in the rock matrix. Fractured media correspond to the limiting case of flat ellipsoids, for which we derive a novel set of simplified formulas. The new formulas have improved numerical stability properties, and require a smaller number of input parameters. To assess their accuracy, we compare the analytical permeability predictions with accurate, three-dimensional finite-element simulations. We also compare the results with a semi-analytical method based on percolation theory and curve fitting, which represents an alternative upscaling approach. A large number of cases is considered, with varying fracture aperture, density, matrix/fracture permeability contrast, orientation, shape and number of fracture sets. The differential method is seen to be the best choice for sealed fractures and thin open fractures. For high-permeable, connected fractures, the semi-analytical method provide the best fit to the numerical data, whereas the differential method breaks down. The two self-consistent methods can be used for both unconnected and connected fractures, although the asymmetric method is somewhat unreliable for sealed fractures. For open fractures, the symmetric method is generally the more accurate for moderate fracture densities, but only the asymmetric method is seen to have correct asymptotic behaviour. The asymmetric method is also surprisingly accurate at predicting percolation thresholds.

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“…It was found that an increase of Young modulus, and index of brittleness and strength enhances the AE or EME amplitude (Hudson et al, 1972;Gol'd et al, 1975;Nitsan, 1977;Khatiashvili, 1984;Carpinteri, 1986Carpinteri, , 1989Carpinteri, , 1990Carpinteri, , 1994Frid et al, 1999Frid et al, , 2000Rabinovitch et al, 2002;Fukui et al, 2005). On the other hand, accumulated experimental and theoretical evidence indicates that the elastic modulus significantly decreases as damage increases, nearing zero as the global fracture approaches (Lockner and Madden 1991;Guéguen et al, 1997;Lin et al, 2004;Shen and Li, 2004;Amitrano and Helmstetter, 2006;Chen, 2012;Chelidze et al, 1988Chelidze et al, , 1990. Characteristically, a very important class of models of material failure is the fiber bundle models (FBMs), which capture the most important aspects of material damage.…”

Section: On the Sensitivity Of The Fracture-induced Em Anomaly To Elamentioning

confidence: 99%

On the puzzling feature of the silence of precursory electromagnetic emissions

Eftaxias

Potirakis

Chélidzé

2013

Nat. Hazards Earth Syst. Sci.

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Abstract. It has been suggested that fracture-induced MHzkHz electromagnetic emissions (EME), which emerge from a few days up to a few hours before the main seismic shock occurrence permit a real-time monitoring of the damage process during the last stages of earthquake preparation, as it happens at the laboratory scale. Despite fairly abundant evidence, electromagnetic (EM) precursors have not been adequately accepted as credible physical phenomena. These negative views are enhanced by the fact that certain "puzzling features" are repetitively observed in candidate fractureinduced pre-seismic EME. More precisely, EM silence in all frequency bands appears before the main seismic shock occurrence, as well as during the aftershock period. Actually, the view that "acceptance of "precursive" EM signals without convincing co-seismic signals should not be expected" seems to be reasonable. In this work we focus on this point. We examine whether the aforementioned features of EM silence are really puzzling ones or, instead, reflect well-documented characteristic features of the fracture process, in terms of universal structural patterns of the fracture process, recent laboratory experiments, numerical and theoretical studies of fracture dynamics, critical phenomena, percolation theory, and micromechanics of granular materials. Our analysis shows that these features should not be considered puzzling.

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Microstructures, percolation thresholds, and rock physical properties

Cited by 91 publications

References 37 publications

Velocity Measurements and Crack Density Determination During Wet Triaxial Experiments on Oshima and Toki Granites

Velocity Measurements and Crack Density Determination During Wet Triaxial Experiments on Oshima and Toki Granites

A 3D Computational Study of Effective Medium Methods Applied to Fractured Media

On the puzzling feature of the silence of precursory electromagnetic emissions

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