Direct observations of damage during unconfined brittle failure of Carrara marble

Tal, Yuval; Evans, Brian; Mok, Ulrich

doi:10.1002/2015jb012749

Cited by 27 publications

(30 citation statements)

References 98 publications

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“…Our results are consistent with other studies on the deformation of Carrara marble under uniaxial or triaxial compressive stress conditions (Tal et al, 2016;Wawersik & Fairhurst, 1970;Wong & Einstein, 2009). Twodimensional strain maps obtained from uniaxial tests on marble (Tal et al, 2016) were decomposed into shear and normal components. The normal and shear components of strain were localized along narrow and diagonal features interpreted as microfractures.…”

Section: 1029/2019jb017381supporting

confidence: 93%

Dynamics of Microscale Precursors During Brittle Compressive Failure in Carrara Marble

et al. 2019

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Microscale heterogeneities influence failure mechanisms in the crust. To track the microstructural changes in rock samples when loaded until failure, we employed a novel experimental technique that couples dynamic X‐ray microtomography imaging with a triaxial deformation apparatus. We studied the brittle failure of Carrara marble under triaxial compression. Dynamic tomographic data revealed the spatial organization of microfractures and damage increments characterizing the precursory activity toward catastrophic failure. We quantified the emergence of scaling relationships between microstructural parameters, including total damage volume, incremental damage volume, the largest connected microfracture, and the applied differential stress. The total volume of microfractures accumulated from the beginning of the experiment as well as the incremental damage showed power law increase. The growth of the largest connected microfracture was related to differential stress as a power law with divergence at failure. The microfracture volume increments were distributed according to a power law with an upper cutoff that itself spanned the entire volume toward failure. These characteristic features of brittle failure in Carrara marble under compression are in agreement with theoretical models that consider failure as a critical phase transition. We also observed that, very close to failure, several power law relationships broke down, which we interpret to be related to the coalescence of the largest microfractures in a finite size volume. Scaling laws and associated exponents computed from our data are compared with predictions made from theoretical and numerical models. Our results show that precursors of macroscopic brittle failure in Carrara marble follow predictable trends.

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Section: 1029/2019jb017381supporting

confidence: 93%

Dynamics of Microscale Precursors During Brittle Compressive Failure in Carrara Marble

et al. 2019

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“…This correlation suggests that regions of high volumetric strain and high shear strain share a common origin, which we attribute to the nucleation, growth, opening, and closing of microfractures and the coupling between them. The postfailure tomogram shows that a higher number of microfractures formed inside grains and propagated across grain boundaries, rather than developing along grain boundaries, in contrast with the behavior observed in Carrara marble (26). The fractures were oriented preferentially toward the direction of the largest compressive stress which is consistent with other studies of similar crystalline rocks (10,11).…”

Section: Dynamics Of Strain Evolutionsupporting

confidence: 87%

“…2. (Inset) The evolution of α toward failure. events and between left-/right-lateral shear events may occur in the form of conjugate microseismicity and faulting or distributed deformation near complex fault geometries, as well as in the surrounding volume (26,39). High-resolution earthquake catalogs in well-instrumented areas show that ongoing seismicity can occur in zones with width of the order of 10 km around major faults (1,3).…”

Section: Implications For Failure In Continental Rocks and Earthquakementioning

confidence: 99%

Volumetric and shear processes in crystalline rock approaching faulting

Renard

McBeck

Kandula

et al. 2019

Proc. Natl. Acad. Sci. U.S.A.

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Understanding the approach to faulting in continental rocks is critical for identifying processes leading to fracturing in geomaterials and the preparation process of large earthquakes. In situ dynamic X-ray imaging and digital volume correlation analysis of a crystalline rock core, under a constant confining pressure of 25 MPa, are used to elucidate the initiation, growth, and coalescence of microfractures leading to macroscopic failure as the axial compressive stress is increased. Following an initial elastic deformation, microfractures develop in the solid, and with increasing differential stress, the damage pervades the rock volume. The creation of new microfractures is accompanied by propagation, opening, and closing of existing microfractures, leading to the emergence of damage indices that increase as powers of the differential stress when approaching failure. A strong spatial correlation is observed between microscale zones with large positive and negative volumetric strains, microscale zones with shears of opposite senses, and microscale zones with high volumetric and shear strains. These correlations are attributed to microfracture interactions mediated by the heterogeneous stress field. The rock fails macroscopically as the microfractures coalesce and form a geometrically complex 3D volume that spans the rock sample. At the onset of failure, more than 70% of the damage volume is connected in a large fracture cluster that evolves into a fault zone. In the context of crustal faulting dynamics, these results suggest that evolving rock damage around existing locked or future main faults influences the localization process that culminates in large brittle rupture events.

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“…The mean of the dilatational strain population increased by larger magnitudes than the shear strain throughout these experiments, suggesting the greater importance of the micromechanisms that produce local dilation rather than shear. Tracking the 2D strain field on the surface of Carrara marble loaded in uniaxial compression also reveals the dominance of shear and dilatational strain events throughout loading, with a greater frequency of dilatational events near macroscopic failure (Tal et al, 2016). DVC analyses on laminated Green River shale (McBeck et al, 2018) provide a different partitioning of the strain modes than observed in the experiments on marble, sandstone and basalt.…”

Section: Brittle Failure Processes In Rocksmentioning

confidence: 82%

The mixology of precursory strain partitioning approaching brittle failure in rocks

McBeck¹,

Ben‐Zion²,

Raffi³

2020

Preprint

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We examine the strain accumulation and localization process throughout twelve triaxial compression experiments on six rock types deformed in an X-ray transparent apparatus. In each experiment, we acquire 50-100 tomograms of rock samples at differential stress steps during loading, revealing the evolving 3D distribution of X-ray absorption contrasts, indicative of density. Using digital volume correlation (DVC) of pairs of tomograms, we build time series of 3D incremental strain tensor fields as the rocks are deformed toward failure. The Pearson correlation coefficients between components of the local incremental strain tensor at each stress step indicate that the correlation strength between pairs of local strain components, including dilation, contraction and shear strain, are moderate-strong in eleven of twelve experiments. In addition, changes in the local strain components from one DVC calculation to the next show differences in the correlations between pairs of strain components. In particular, the correlation of the local changes in dilation and shear strain tends to be stronger than the correlation of changes in dilation-contraction and contraction-shear strain. In eleven of twelve experiments, the most volumetrically frequent mode of strain accommodation includes a synchronized increase in multiple strain components. Early in loading, under lower differential stress, the most frequent strain accumulation mode involves the paired increase in dilation and contraction at neighboring locations. Under higher differential stress, the most frequent mode is the paired increase in dilation and shear strain. This mode is also the first or second most frequent throughout each complete experiment. Tracking the mean values of the strain components in the sample and the volume of rock that each component occupies reveals fundamental differences in the nature of strain accumulation and localization between the volumetric and shear strain modes. As the dilative strain increases in magnitude throughout loading, it tends to occupy larger volumes within the rock sample and thus delocalizes. In contrast, the increasing shear strain components (left- or right-lateral) do not necessarily occupy larger volume and so involve localization. Consistent with these evolutions, the correlation length of the dilatational strains tends to increase by the largest amounts of the strain components from lower to higher differential stress. In contrast, the correlation length of the shear strains does not consistently increase or decrease with increasing differential stress.

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Direct observations of damage during unconfined brittle failure of Carrara marble

Cited by 27 publications

References 98 publications

Dynamics of Microscale Precursors During Brittle Compressive Failure in Carrara Marble

Dynamics of Microscale Precursors During Brittle Compressive Failure in Carrara Marble

Volumetric and shear processes in crystalline rock approaching faulting

The mixology of precursory strain partitioning approaching brittle failure in rocks

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