Quantification of microcrack characteristics and implications for stiffness and strength of granite

Griffiths, Luke; Heap, Michael; Baud, Patrick; Schmittbuhl, Jean

doi:10.1016/j.ijrmms.2017.10.013

Cited by 168 publications

(79 citation statements)

References 55 publications

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“…Hydrothermal fluids and heat input may also dissolve or break down rock-forming minerals, thus creating additional permeable porous pathways for fluid flow (e.g., Cant et al, 2018;Farquharson et al, 2019;Heap et al, 2012;Kanakiya et al, 2017;Nemčok et al, 2007). Alternatively, hydrothermal fluids may induce the precipitation of minerals (e.g., clays, salts, carbonates, and silica polymorphs) within the pores and cracks (e.g., Rowland & Sibson, 2004;Griffiths et al, 2017;Kanakiya et al, 2017) and thereby decrease permeability (e.g., Heap et al, 2017). The permeability evolution of the reservoir rock is ultimately governed by the temperature, stress field, and chemistry of the system (fluids and solids), which control fluid convection (Fournier, 1985, and references therein).…”

Section: Introductionmentioning

confidence: 99%

Increasing the Permeability of Hydrothermally Altered Andesite by Transitory Heating

Mordensky

Kennedy

Villeneuve

et al. 2019

Geochem Geophys Geosyst

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Changes in permeability can impact geological processes, geohazards, and geothermal energy production. In hydrothermal systems, high‐temperature heat sources drive fluid convection through the pore network of reservoir rocks. Additionally, thermal fluctuations may induce microfracturing and affect the mineralogical stability of the reservoir rock, thus modifying the fluid pathways and affecting permeability and strength. This study describes the results of thermal heating events lasting several hours on a “moderately altered” plagioclase‐clinochlore‐calcite‐quartz andesite and a “highly altered” plagioclase‐clinozoisite‐quartz‐clinochlore andesite from the Rotokawa Geothermal Field, New Zealand. We use a low thermal gradient (~1.2 °C/min) in an H2O‐saturated, 20‐MPa pressure environment to constrain changes in petrophysical properties associated with transitory thermal phenomena between 350 and 739 °C. As the treatment temperature increases, the mass reduces, while porosity and permeability increase. These effects were greater in the “moderately altered” andesite than in the “highly altered” andesite. Microfracturing is responsible for these changes at lower temperatures (e.g., ≤400 °C). At higher temperatures (e.g., >400 °C), microfracturing remains partially responsible for these rock property changes (e.g., higher permeability); however, these changes are also a product of clinochlore, quartz, and (when present) calcite reacting out of the altered andesite, and increasing porosity. We propose that at temperatures >400 °C, volumetric phase changes associated with heat‐driven reactions in a wet environment can contribute to microcracking and porosity/permeability changes. Our data support observations where high‐temperature conditions at the margins of magma bodies can be associated with substantial increased permeability and decreased strength.

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Section: Introductionmentioning

confidence: 99%

Increasing the Permeability of Hydrothermally Altered Andesite by Transitory Heating

Mordensky

Kennedy

Villeneuve

et al. 2019

Geochem Geophys Geosyst

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“…Because our model results are confined to microscopic damage, which is defined strictly in our model as a decrease in stiffness, direct comparisons to typically measured parameters in field and laboratory studies of bedrock weathering are also limited. Recent studies have compared measurements in maximum compressive and tensile strengths to fracture densities and chemical mass losses in weathering rock (Griffiths et al, ; Goodfellow et al, ). While these studies reveal correlations between mechanical strength, fracture density, and chemical properties, they are not directly comparable to our model results.…”

Section: Discussionmentioning

confidence: 99%

Mineral Weathering and Bedrock Weakening: Modeling Microscale Bedrock Damage Under Biotite Weathering

et al. 2019

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Bedrock weakening is of wide interest because it influences landscape evolution, chemical weathering, and subsurface hydrology. A longstanding hypothesis states that bedrock weakening is driven by chemical weathering of minerals like biotite, which expand as they weather and create stresses sufficient to fracture rock. We build on recent advances in rock damage mechanics to develop a model for the influence of multimineral chemical weathering on bedrock damage, which is defined as the reduction in bedrock stiffness. We use biotite chemical weathering as an example application of this model to explore how the abundance, aspect ratio, and orientation affect the time‐dependent evolution of bedrock damage during biotite chemical weathering. Our simulations suggest that biotite abundance and aspect ratio have a profound effect on the evolution of bedrock damage during biotite chemical weathering. These characteristics exert particularly strong influences on the timing of the onset of damage, which occurs earlier under higher biotite abundances and smaller biotite aspect ratios. Biotite orientation, by contrast, exerts a relatively weak influence on damage. Our simulations further show that damage development is strongly influenced by the boundary conditions, with damage initiating earlier under laterally confined boundaries than under unconfined boundaries. These simulations suggest that relatively minor differences in biotite populations can drive significant differences in the progression of rock weakening. This highlights the need for observations of biotite abundance, aspect ratio, and orientation at the mineral and field scales and motivates efforts to upscale this microscale model to investigate the evolution of the macroscale fracture network.

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“…Montages of high‐resolution (225 pixels per millimeter) BSE images taken at a magnification of ×100 from each thin section were taken on a FEI Quanta 200F environmental SEM at the University of Glasgow (UK). BSE images are very practical for microscale crack and pore mapping, because different minerals are represented with different grey levels and black represents void space, that is, pores and fractures (Farrell et al, ; Farrell & Healy, ; Griffiths et al, ; Wibberley et al, ). Fracture maps were produced by manually tracing all the visible cracks over the of the BSE mosaic using a vector graphic editor (Adobe Illustrator TM ).…”

Section: Methodsmentioning

confidence: 99%

Detecting the Onset of Strain Localization Using Two‐Dimensional Wavelet Analysis on Sandstone Deformed at Different Effective Pressures

et al. 2018

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Laboratory brittle deformation experiments have shown that a rapid transition exists in the behavior of porous materials under stress: At a certain point, early formed and spatially distributed tensile cracks interact and coalesce forming a shear plane. In this work, we present and apply a novel image processing tool that is able to quantify this transition between distributed (“stable”) damage accumulation and localized (“unstable”) deformation, in terms of the size, density, and orientation of cracks at the point of strain localization. Our technique, based on a two‐dimensional Morlet wavelet analysis, can recognize, extract, and visually separate the multiscale changes occurring in the crack network during the deformation process. We first performed a series of triaxial experiments (σ1>σ2=σ3) on core plugs of Hopeman Sandstone (Scotland, UK) at different effective pressures (from 5 to 30 MPa). We then processed high‐resolution backscattered electron microscope images of thin sections of these core plugs and found differences in the strain localization process as effective pressure was increased. The critical length of tensile cracks required before the onset of strain localization was reduced from 0.24 to 0.15 mm as the effective pressure was increased to 30 MPa, resulting in a narrow fracture zone. Critically, by comparing patterns of fractures in these deformed sandstone samples, we can quantitatively explore the relationship between the observed geometry of the cracks and the inferred mechanical processes. This will eventually help us to better understand the physics underlying the initiation of catastrophic events, such as earthquakes, landslides, and volcanic eruptions.

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Quantification of microcrack characteristics and implications for stiffness and strength of granite

Cited by 168 publications

References 55 publications

Increasing the Permeability of Hydrothermally Altered Andesite by Transitory Heating

Increasing the Permeability of Hydrothermally Altered Andesite by Transitory Heating

Mineral Weathering and Bedrock Weakening: Modeling Microscale Bedrock Damage Under Biotite Weathering

Detecting the Onset of Strain Localization Using Two‐Dimensional Wavelet Analysis on Sandstone Deformed at Different Effective Pressures

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