Dynamics of Microscale Precursors During Brittle Compressive Failure in Carrara Marble

Kandula, Neelima; Cordonnier, B.; Boller, Élodie; Weiss, Jérôme; Dysthe, Dag Kristian; Renard, François

doi:10.1029/2019jb017381

Cited by 51 publications

(46 citation statements)

References 74 publications

(155 reference statements)

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“…An estimate for the correlation length exponent (1.15) for Carrara marble (Kandula et al, 2019) falls almost exactly halfway between the exponents for Ailsa Craig microgranite found here (0.65 for the heterogeneous sample and 1.75 for the homogeneous sample). However, the Carrara marble exponent was estimated by assuming the failure stress a priori, so it is not directly comparable with our results.…”

Section: 1029/2020jb019642supporting

confidence: 76%

Catastrophic Failure: How and When? Insights From 4‐D In Situ X‐ray Microtomography

et al. 2020

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Catastrophic failure of brittle rocks is important in managing risk associated with system‐sized material failure. Such failure is caused by nucleation, growth, and coalescence of microcracks that spontaneously self‐organize along localized damage zones under compressive stress. Here we present X‐ray microtomography observations that elucidate the in situ micron‐scale processes, obtained from novel tri‐axial compression experiments conducted in a synchrotron. We examine the effect of microstructural heterogeneity in the starting material (Ailsa Craig microgranite; known for being virtually crack‐free) on crack network evolution and localization. To control for heterogeneity, we introduced a random nanoscale crack network into one sample by thermal stressing, leaving a second sample as‐received. By assessing the time‐dependent statistics of crack size and spatial distribution, we test the hypothesis that the degree of starting heterogeneity influences the order and predictability of the phase transition between intact and failed states. We show that this is indeed the case at the system‐scale. The initially more heterogeneous (heat‐treated) sample showed clear evidence for a second‐order transition: inverse power law acceleration in correlation length with a well‐defined singularity near failure and distinct changes in the scaling exponents. The more homogeneous (untreated) sample showed evidence for a first‐order transition: exponential increase in correlation length associated with distributed damage and unstable crack nucleation ahead of abrupt failure. In both cases, anisotropy in the initial porosity dictated the fault orientation, and system‐sized failure occurred when the correlation length approached the grain size. These results have significant implications for the predictability of catastrophic failure in different materials.

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Section: 1029/2020jb019642supporting

confidence: 76%

Catastrophic Failure: How and When? Insights From 4‐D In Situ X‐ray Microtomography

et al. 2020

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“…In addition, we develop a method that links one or more fractures at the previous loading step (tn) to the next loading step (tn+1) ( Figure 3). This development is the central difference between this new method and the previous method of tracking fractures in X-ray tomography data developed by Kandula et al (2019). The previous method did not allow linking more than one fracture in tn to a fracture in tn+1.…”

Section: Identifying Propagating and Coalescing Fracturesmentioning

confidence: 99%

“…The previous method did not allow linking more than one fracture in tn to a fracture in tn+1. Thus, Kandula et al (2019) could identify when an individual fracture gained or lost volume from one loading step (and tomogram) to the next. However, this analysis could not differentiate between fractures that gained volume because one fracture propagated and opened, or because several fractures propagated and linked with each other (i.e., coalesced).…”

Section: Identifying Propagating and Coalescing Fracturesmentioning

confidence: 99%

The competition between fracture nucleation, propagation and coalescence in the crystalline continental upper crust

McBeck

Zhu

Renard

2020

Preprint

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Abstract. Different modes of fracture growth produce fracture networks with distinctive geometric attributes that exert important controls on the extent of fluid-rock interactions. We perform in situ X-ray tomography triaxial compression experiments on monzonite to investigate the influence of fracture nucleation, preexisting fracture propagation, and coalescence on fracture network development in crystalline rocks under crustal conditions. We impose a confining pressure of 20–35 MPa and then increase the differential stress in steps until the rock fails macroscopically. After each stress step we acquire a three-dimensional (3D) X-ray adsorption coefficient field from which we extract the 3D fracture network. To examine the influence of pore fluid on fracture network development, we perform two experiments under nominally-dry conditions and one under water-saturated conditions with 5 MPa pore fluid pressure. We develop a method of tracking individual fractures between subsequent tomographic scans that identifies whether fractures grow from the coalescence and linkage of several fractures or from the propagation of a single fracture. Throughout loading until shortly before failure in all of the experiments, the volume of coalescing fractures is smaller than the volume of propagating fractures, indicating that fracture propagation dominates coalescence. Immediately preceding failure, however, the volume of coalescing fractures is at least double the volume of propagating fractures in the experiments deformed at nominally dry conditions. In the water-saturated sample, although the volume of coalescing fractures increases during this stage, the volume of propagating fractures remains dominant. The influence of stress corrosion cracking associated with hydration reactions at fracture tips and/or dilatant hardening may explain the observed difference in fracture development under dry and water-saturated conditions. Our experimental data on fracture growth at different conditions provide new constraints in assessing fluid flow in subsurface fracture networks that are central to energy and environmental engineering practices.

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“…The rock samples used here are cylindrical cores, 5 mm in diameter and 10 mm in height, drilled from a block of Carrara marble. They come from the same block used in the experiments of rock failure performed in Kandula et al (2019). Carrara marble is a coarse-grained, nearly pure calcite rock with grain size in the range of 100-200 μm and initial (undeformed) porosity less than 1%.…”

Section: Dynamic Synchrotron In Situ Experimentsmentioning

confidence: 99%

“…Our experimental setup contains an important improvement compared with a previous study where Carrara marble was deformed to failure under increasing stress conditions (Kandula et al, 2019). In the present study, a LVDT sensor was added on the Hades rig.…”

Section: 1029/2020jb020354mentioning

confidence: 99%

Creep Burst Coincident With Faulting in Marble Observed in 4‐D Synchrotron X‐Ray Imaging Triaxial Compression Experiments

et al. 2020

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Faults in carbonate rocks show both seismic and aseismic deformation processes, leading to a wide range of slip velocities. We deformed two centimeter-scale cores of Carrara marble at 25°C and imaged the nucleation and growth of faults using dynamic synchrotron X-ray microtomography. The first sample experienced a constant confinement of 30 MPa and no pore fluid. The second sample experienced confinement in the range 35-23 MPa and water as a pore fluid at 10 MPa pore pressure. We increased the axial stress by steps until creep deformation occurred and imaged deformation in 4-D. The samples deformed with a quasi-constant or increasing strain rate when the differential stress was constant, a process called creep. However, for both samples, we also observed transient events that include the acceleration of creep, that is, creep bursts, phenomena similar to slow slip events that occur in continental active faults. During these transient creep events, strain rates increase and correlate in time with strain localization and the slow development of system-spanning fault networks. In both samples, the acceleration of opening and shearing of microfractures accommodated creep bursts. High-resolution time-lapse X-ray microtomography imaging and digital image correlation during triaxial deformation quantify creep in laboratory faults at subgrain spatial resolution. This work demonstrates that transient creep events, that is, creep bursts or slow slip events, correlate with the nucleation and slow growth of faults and not only with slip on preexisting faults. Plain Language Summary Active faults may slip at velocities close to 1 m/s during earthquakes and may also slip at much slower rates, in creep. Sometimes such creep is continuous in time; sometimes it is transient and occurs as creep bursts, also called slow slip events. Using state-of-the-art synchrotron X-ray imaging of core samples of Carrara marble deformed under constant stress conditions and room temperature, we identified such creep bursts. Our 4-D imaging technique allows seeing through the sample and characterizing the microphysical processes that produce creep bursts. Results show that the acceleration of microfractures nucleation, growth, and coalescence in the sample may lead to the formation of system-spanning faults that coincide in time with the macroscopically observed creep burst. These results demonstrate that creep bursts may not only correspond to slow slip events on active preexisting faults but may also indicate the slow development of new active faults.

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Dynamics of Microscale Precursors During Brittle Compressive Failure in Carrara Marble

Cited by 51 publications

References 74 publications

Catastrophic Failure: How and When? Insights From 4‐D In Situ X‐ray Microtomography

Catastrophic Failure: How and When? Insights From 4‐D In Situ X‐ray Microtomography

The competition between fracture nucleation, propagation and coalescence in the crystalline continental upper crust

Creep Burst Coincident With Faulting in Marble Observed in 4‐D Synchrotron X‐Ray Imaging Triaxial Compression Experiments

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