Crack Aperture Research Articles

Thermally-induced cracks and their effects on natural and industrial geomaterials

Thermal stress can result in significant changes in the mechanical and transport properties of building materials, especially in terms of cracking. Three building materials were studied: two concretes, a siliceous and a calcareous one, and a natural calcareous rock, the Tuffeau. The samples were subjected to thermal shock, repetitive heating-cooling cycles, and high temperature heating in order to analyze the effects of maximum temperature, cooling rate, and repetitive heating on the three materials. The induced cracks were then characterized by physical and hydraulic measurements, namely elastic wave velocities, porosity and effective thermal conductivity. Elastic wave velocities were used to determine crack density while effective thermal conductivity was used to determine crack connectivity. Cracks were also quantitatively described through direct microstructural observations using scanning electron microscopy. Results show the effectiveness of the different protocols in inducing cracks. Unexpectedly, repetitive heating-cooling cycles caused the most significant sample damage, whatever the sample. A second main result is based on the comparison of the different materials. It was found that the behavior of the two concretes was very similar: the stronger the thermal treatment, the more the crack density and connectivity increased, albeit with a slight difference in that the siliceous concrete appeared to be less resistant to sharp thermal variations. This is interpreted as being linked to microstructural effects: in the siliceous concrete, we observed cracks that nucleated around and inside grains, but not in the calcareous concrete. Lastly, the behavior of the Tuffeau limestone was different from that of the concretes: when crack density increased, the crack connectivity and the porosity both decreased. This different behavior is interpreted in the light of microstructural observations of the crack apertures: the thermally induced cracks in Tuffeau are too small to influence the effective thermal connectivity measurement and to allow fluid flow during the porosity measurement, whereas in the concretes, cracks were observed to be much more open. As an outlook, we discuss a possible equivalent test to the normalized fire protocol, performed at high temperature, to test the fire resistance of materials.

Influence of Stress and Crack Patterns on the Sensitive Characteristics of Fissure Sandstone Permeability under Hydromechanical Coupling

The stress-sensitive of seepage characteristics after rock fracture has a crucial effect on the formation and closure of seepage channels, and it is important to study the sensitivity of fracture permeability for engineering seepage prevention. The aim of the current study was to investigate the permeability law of different fracture modes under unloading action. Firstly, the physical and mechanical parameters of the Voronoi polygon block and joint were fitted with rock properties obtained in the laboratory based on the fracture characteristics of triaxial seepage experiment samples. Crack reconstruction technology and a new hydraulic parameter fitting method were used to obtain the hydraulic aperture of microjoints and macrocracks. Then, six single crack models and four models based on typical fracture characteristics of rock samples were established to study the variation of the hydraulic aperture of microcracks and macroscopic cracks in unloading environment and the morphology of the main seepage passages, to explore the seepage characteristics of different angle cracks under different unloading stress paths, and to analyze the law of seepage variation of different crack forms under different stress environments. The results indicated that a horizontal hydraulic aperture is more sensitive to axial stress than a vertical hydraulic aperture and that a vertical hydraulic aperture is more sensitive to confining stress than a horizontal hydraulic aperture. For a single crack model, the sensitivity of a 70–90-degree crack to confining pressure is greater than that of a 40–60-degree crack. The axial stress sensitivity of a 40–60-degree crack is greater than that of a 70–90-degree crack. For a typical fracture model, under the same stress conditions, the sensitivity of four typical cracks to confining pressure is greater than that to axial pressure.

Mathematical modeling of microcrack growth in source rock during kerogen thermal maturation

The success of hydraulic fracturing and increasing use of basin-modeling packages drive the need to understand the effects of hydrocarbon (HC) generation on the mechanical properties of source rocks. A better understanding of relationships among geological, geochemical, and geomechanical parameters can potentially reduce the uncertainties associated with conventional and unconventional prospect evaluation. We present a simulation of microcrack growth based on a three-dimensional source-rock system. Upon thermal maturation, the kerogen transforms into lighter products, most of which are HCs. The generated products exert excessive pore pressure to the system resulting from the effect of volume expansion; this pressure is released through the expansion of pore space and formation of microcracks. Using linear elasticity and linear elastic fracture mechanics, our model calculates microcrack sizes (surface areas, lengths, apertures, and volumes) and the amount of overpressure throughout the maturation process. We validated this model with experimental data from Kobchenko et al. (2011), and performed sensitivity analysis for both laboratory and geological settings. Much larger microcracks are generated in laboratory settings compared to the subsurface because of the lack of overburden, resulting in secondary porosity over 100 times larger than the original organic porosity and crack lengths obtaining millimeter scale. In contrast, microcracks are much smaller in geological settings because of the presence of significant overburden and stiffer rock frames: the crack apertures are in the submicron regime with a crack length ranging from 100 to 300 μm. The formation of microcracks connects isolated microscale HC pockets, providing pathways for primary migration.

Source Properties and Triggering Processes of Long‐Period Events Beneath Volcanoes Inferred From an Analytical Formula for Crack Resonance Frequencies

AbstractLong‐period (LP) seismic events are thought to arise from the oscillations of a fluid‐filled resonator. The fluid properties and resonator geometry of LP sources have been estimated by comparing observed frequencies to those calculated from a crack model. However, simultaneous determinations of crack geometry and fluid properties have been based on time‐consuming crack model simulations. We developed an alternative method to estimate these crack model parameters using a recently proposed analytical formula. We applied it to LP events at Kusatsu‐Shirane volcano, Japan and Galeras volcano, Colombia, which have been thought to be generated by resonances of cracks filled with misty and dusty gases, respectively. Our estimates of the crack model parameters displayed temporal changes in both crack geometry and fluid properties, which previous studies have not shown. Our estimated parameters had common features at the two volcanoes: (1) Crack volumes and gas‐weight fractions of water vapor in the cracks were positively correlated, and (2) mist and dust volumes were proportional to the product of crack aperture and crack length or width. From these features, we inferred that the LP events were triggered by volumetric changes associated with condensation of water vapor exsolved from magma at Kusatsu‐Shirane and by fragmentation of vesiculated magma intruded into the crack at Galeras. This study demonstrates a useful new method to investigate the state of fluids and triggering processes of LP events.

Modeling fracture cementation processes in calcite limestone: a phase-field study

The present work investigates the influence of crack opening rates on the development of four important calcite vein morphologies, namely fibrous, elongate-blocky, partially open, and euhedral, as a result of bitaxial growth in syntaxial veins using a multiphase-field model. The continued fracturing that occurs during synkinematic cementation in these veins is simulated using the geometric shift algorithm. The stark resemblance of the numerically sealed vein microstructures with the natural samples in terms of structural characteristics as well as remaining pore space signifies a dominant role of crack opening rates in the resulting morphological patterns. Further, simulation results of slow crack opening rates reveal that non-uniform fibers of variable lengths are formed when initial crack aperture is small, due to suppression of growth competition and vice versa.

Effects of straw incorporation on desiccation cracking patterns and horizontal flow in cracked clay loam

Shrink-swell soil cracks upon dehydration, providing potentially preferential pathways for gravity-driven flow and contaminants transport. The process of crack-preferential flow is swelling-dependent, due to the dynamical changes in porous structure (cracks) in response to moisture variation. Incorporating straw into soils modifies the behavior of soil cracking, soil deformation characteristics and hydraulic properties, which has a possibility of inhibiting propagation of crack-preferential flow. The objectives of this study were to investigate the effects of straw incorporation on the crack patterns and preferential flow and to reveal how the swelling dynamics of cracked soils intervene the crack-preferential flow process. The soils were treated with three densities of straw incorporation. We investigated the horizontal infiltration in uncracked and cracked soils amended with straw and exposed to wetting-drying cycles. Horizontal flow patterns and the dynamics of crack closure were recorded with a digital camera mounted above the specimen. The propagation characteristics of the wetting front (WF) were quantified using digital image processing and morphological algorithms. The results showed that straw incorporation markedly inhibited the cracking degree and rendered the crack patterns more fragmented. Significant fluctuations in the infiltration rate were observed in cracked soils in the early stages of the infiltration process, and the straw incorporation attenuated the fluctuations of the infiltration rate. Normal crack apertures (perpendicular to the infiltration direction) blocked the continuous capillary-driven flow as air barriers and decelerated the infiltration rate in comparison to uncracked soils. The longitudinal cracks (along the infiltration direction) served as preferential pathways and facilitated the early-stage infiltration, but the duration of crack-preferential flow was dominated by the swelling rate of the aggregated soil clods. The tortuosity of the WF revealed that the flow regime transitioned from crack-preferential flow to matrix flow as the infiltration process progressed. Our results suggest that the crack-preferential flow becomes less pronounced as the cracks become progressively narrower, resulting from the swelling dynamics of the soil matrix. The fluctuations in the infiltration rate and the developing extent of crack flow can be attenuated by straw incorporation through restricting crack ratio and modifying crack morphology. Rice straw at a threshold density (experimentally determined) could be incorporated into soils to restrict the flow regime transition point (from crack preferential flow to matrix flow) to the depths of root zones, thus effectively precluding deep percolation induced by the cracks in shrink-swell soils.

On the threshold crack opening effect on the intrinsic permeability of localized macro-cracks in concrete samples under Brazilian test conditions

The Brazilian (indirect tensile strength) test is widely adopted for studying the permeability evolution of single localized macro-cracks in concrete samples. In most of these studies, the existence of a threshold crack opening effect on the crack permeability is argued, in particular when permeability measurements are performed on previously cracked samples (i.e., on residual cracks). Based on recent experimental results obtained by the authors, the present contribution aims to show that performing permeability measurements in real-time with the crack opening process (i.e., under loading) ensures improving the results quality and makes their interpretation less ambiguous. It is shown that no threshold crack opening effect is detected in the explored range of crack opening displacements. Although presented results do not allow to conclude concerning the existence of such an effect, they point out several critical aspects concerning the interpretations usually provided. In particular, based on the comparison between present and reference results, it is proposed to interpret literature observations as direct consequences of some artifacts inherent to standard experimental procedures, such as the impossibility of distinguishing between crack and porous medium contributions to the measured mass flow rate, crack re-closure due to unloading and/or self-healing phenomena, an inaccurate estimation of the crack apertures corresponding to flow measurements.

Study of the effect of upstream slope on water pressure in concrete gravity dam

In recent past, some research work has been done to considerate properly the water pressure in concrete gravity dam to take it into account for crack propagation. However, a two-dimensional finite element model is developed to calculate the water pressure under hydrostatic pressure on two geometries cases of Kinta concrete gravity dam.The results show the upstream slope affects considerably the water pressure at the dam bottom in case one comparing to case two due to vertical hydrostatic pressure, leads to important displacement at the crest of the dam that influence the global behavior of the dam inducing to aperture of cracks.

Experimental study on propagation behavior of three-dimensional cracks influenced by intermediate principal stress

Many laboratory experiments on crack propagation under uniaxial loading and biaxial loading have been conducted in the past using transparent materials such as resin, polymethyl methacrylate (PMMA), etc. However, propagation behaviors of three-dimensional (3D) cracks in rock or rock-like materials under tri-axial loading are often considerably different. In this study, a series of true tri-axial loading tests on the rock-like material with two semi-ellipse pre-existing cracks were performed in laboratory to investigate the acoustic emission (AE) characteristics and propagation characteristics of 3D crack groups influenced by intermediate principal stress. Compared with previous experiments under uniaxial loading and biaxial loading, the tests under true tri-axial loading showed that shear cracks, anti-wing cracks and secondary cracks were the main failure mechanisms, and the initiation and propagation of tensile cracks were limited. Shear cracks propagated in the direction parallel to pre-existing crack plane. With the increase of intermediate principal stress, the critical stress of crack initiation increased gradually, and secondary shear cracks may no longer coalesce in the rock bridge. Crack aperture decreased with the increase of intermediate principal stress, and the failure is dominated by shear fracturing. There are two stages of fracture development: stable propagation stage and unstable failure stage. The AE events occurred in a zone parallel to pre-existing crack plane, and the AE zone increased gradually with the increase of intermediate principal stress, eventually forming obvious shear rupture planes. This shows that shear cracks initiated and propagated in the pre-existing crack direction, forming a shear rupture plane inside the specimens. The paths of fracturing inside the specimens were observed using the Computerized Tomography (CT) scanning and reconstruction.

Experimental study on water exchange between crack and clay matrix

Cracks in soil provide significant preferential pathways for contaminant transport and rainfall infiltration. Water exchange between the soil matrix and crack is crucial to characterize the preferential flow, which is often quantitatively described by a water exchange ratio. The water exchange ratio is defined as the amount of water flowing from the crack into the clay matrix per unit time. Most of the previous studies on the water exchange ratio mainly focused on cracked sandy soils. The water exchange between cracks and clay matrix were rarely studied mainly due to two reasons: (1) Cracks open upon drying and close upon wetting. The deformable cracks lead to a dynamic change in the water exchange ratio. (2) The aperture of desiccation crack in clay is narrow (generally 0.5 mm to 5 mm) which is difficult to model in experiments. This study will investigate the water exchange between a deformable crack and the clay matrix using a newly developed experimental apparatus. An artificial crack with small aperture was first fabricated in clay without disturbing the clay matrix. Water content sensors and suction sensors were instrumented at different places of the cracked clay to monitor the water content and suction changes. Results showed that the water exchange ratio was relatively large at the initial stage and decreased with the increasing water content in clay matrix. The water exchange ratio increased with increasing crack apertures and approached the largest value when the clay was compacted at the water content to the optimal water content. The effective hydraulic conductivity of the crack-clay matrix interface was about one order of magnitude larger than that of saturated soil matrix.

Coupled hydraulic-mechanical simulation of seasonally induced processes in the Mont Terri rock laboratory (Switzerland)

This paper focuses on hydraulic-mechanical effects in the Mont Terri rock laboratory (Switzerland) and investigates their impact on pore pressure, the convergence of a niche and the evolution of pre-existing cracks in the wallrock of the niche. A comparison of measurements with numerical simulation results is conducted. The presented in situ measurements include long-term data on temperature, relative humidity, and niche convergence, as well as crackmeter and jointmeter measurements determining the aperture of a bedding-parallel crack. Furthermore, time-domain-reflectometry measurements were carried out in a borehole located in the niche wall close to the crack. They provide information on the water content of the claystone. The numerical simulation is carried out with OpenGeoSys. It contains a 2-dimensional coupled hydraulic-mechanical model considering orthotropy, swelling and shrinkage effects, linear elastic material behaviour and an excavation damaged zone characterized by a zone of lower rock strength. An additional focus is laid on the evolution of cracks in the wallrock of the niche. The presented model approach allows a prediction of the temporal evolution of a desaturated zone incorporating a seasonally influenced part. The comparison with measured water contents yields good agreement. Simulation results and measurements consistently predict a convergence of the niche. The evolution of the crack aperture is influenced by long-term as well as seasonallyinfluenced effects. Due to the convergence of the niche, the long-term trend is characterized by closure of the crack. Furthermore, the seasonally influenced desaturation in winter results in opening of the crack, while the resaturation in the warm and wet summer months leads to closure of the crack. Finally, the comparison of simulation results with measurements indicates qualitative agreement. As a matter of fact, the numerical model seems to represent significant effects concerning the evolution of the crack aperture of a single crack.

Identification of Microstructural Properties of Shale by Combined Use of X-Ray Micro-CT and Nanoindentation Tests

Shale, a fine-grained sedimentary rock, is composed of highly compacted clay particles, nanometric porosity and silt-sized particles of other minerals. In this paper, a combined use of X-Ray micro-CT and nanoindentation tests is proposed for the qualitative and quantitative characterization of this material. The individual methods are utilized at different scales of observation: nanoindentation at nano and micro level while the X-ray microtomography at the meso scale. For the purpose of mechanical morphology evaluation, the grid nanoindentation measurements are carried out resulting in the overall histograms of indentation properties, i.e. indentation modulus and hardness. Tests are performed at different values of applied load and in two directions: parallel and normal to the plane of isotropy, x1 and x3, respectively. The deconvolution technique is used for the segmentation of the material constituents with respect to mechanical properties. Based on the results obtained from nanoindentation testing at nano scale, the shale matrix composition is identified, namely: the number of constituents, their volume fractions as well as the mechanical properties. In addition, at micro scale, the homogenized parameters of the intact shale material are determined. On the other hand, based on the X-ray microtomography imaging results, the geometry of the shale structure at meso scale is investigated. The studies focus on observation of the evolution of 3D crack network in the samples of shale under uniaxial compression at different levels of load. The research includes three series of scans for eight samples, previously subjected to loading. Based on the acquired images, some statistical morphological measures are calculated, i.e. volume fraction of cracks, tortuosity and crack aperture spatial distribution. In addition, the effective parameters of anisotropic permeability and their changes induced by different levels of loading are estimated using Kozeny-Carman formula.

Nonlinear model characterizing stress–strain relationship and permeability change of contact compression fracture at closing stage

Understanding the stress–strain relationship and permeability change for contact compression fracture at closing stage has been a hot issue for a long time. Previous investigations of this topic were mainly focused on experimental tests; however, theoretical approaches were rarely reported. Based on this, this paper focuses on the contact fracture at closing stage when rock is uniaxially loaded, and then a theoretical model is proposed. Based on the change of fracture elasticity modulus, it shows that as crack apertures are gradually reduced in the loading process, the permeability of rock sample will decrease progressively. This scenario shows that theoretical computation matches well with the experimental results. Finally, the effects of ratio of sample size to fracture aperture (n), pore pressure (P), and initial aperture (b) on stress–strain relationship and permeability change for contact compression fracture at closing stage are analyzed.

Changes in geophysical properties caused by fluid injection into porous rocks: analytical models

ABSTRACTAnalytical models are provided that describe how the elastic compliance, electrical conductivity, and fluid‐flow permeability of rocks depend on stress and fluid pressure. In order to explain published laboratory data on how seismic velocities and electrical conductivity vary in sandstones and granites, the models require a population of cracks to be present in a possibly porous host phase. The central objective is to obtain a consistent mean‐field analytical model that shows how each modeled rock property depends on the nature of the crack population. The crack populations are described by a crack density, a probability distribution for the crack apertures and radii, and the averaged orientation of the cracks. The possibly anisotropic nature of the elasticity, conductivity, and permeability tensors is allowed for; however, only the isotropic limit is used when comparing to laboratory data. For the transport properties of conductivity and permeability, the percolation effect of the crack population linking up to form a connected path across a sample is modeled. However, this effect is important only in crystalline rock where the host phase has very small conductivity and permeability. In general, the importance of the crack population to the transport properties increases as the host phase becomes less conductive and less permeable.

Damage mechanism of slab track under the coupling effects of train load and water

The damage mechanism of slab track under the coupling effect of train load and water was studied in this research. Based on the law of mass conservation and momentum theorem, the hydrodynamic pressure expression was derived by using the control volume method. The effects of load characters, water viscosity, and crack shape were analyzed in this paper. In order to describe the stress field singularity of crack tip, the quarter-points elements at the crack tip were established, and the maximum tensile-stress criterion and mixed fracture criterion were used to analyze the coupled hydro-mechanical fracture of slab track. Through the presented analysis, it was determined that, the effect of water viscosity on hydrodynamic pressure is negligible when crack aperture is greater than 2mm, and the value of hydrodynamic pressure depends linearly on axle load and is proportional to the square of train speed. The train speed is an important factor to affecting the crack propagation, and the crack propagation rate increases with the increasing train speed. It is concluded from the research that the mixed-model fracture criterion is more appropriate to analyze the coupled hydro-mechanical fracture of slab track than the maximum tensile-stress criterion.

Multi-scale study on the deformation and fracture evolution of clay rock sample subjected to desiccation

The aim of this paper is to compare and discuss the values of strains and crack apertures associated with desiccation cracks measured in Tournemire clay rock at different scales (micrometer to decimeter). Experimental investigations in the laboratory were conducted on one clay rock sample subjected to a desiccation process. Two faces with dimensions of 20×20mm2 (i.e., macroscopic scale) and 5.1×4.1mm2 (i.e., mesoscopic scale) were analyzed. The induced hydric strains and desiccation cracking were monitored by digital image correlation combined with a new algorithm (H-DIC). The results were compared with the data of Hedan et al. (2014) at the gallery scale (decimeter) and those of Wang et al. (2013) at the microscopic scale (micrometer).Our laboratory study yielded the following phenomenological results. First, the displacement fields revealed the presence of sub-horizontal cracks associated with the direction of bedding planes and sub-vertical cracks, as previously observed in a gallery front in Tournemire Station. Second, when the relative humidity (RH) decreased between 98% and 33%, the crack aperture kinematics at the macroscopic scale (centimeter) was divided into three steps: (i) a phase of opening and closure, (ii) a phase of only gradual closure, and (iii) a final phase in which the desiccation cracks closed. Only phases (ii) and (iii) were observed at the mesoscopic scale (millimeter), revealing that the kinematics of cracks depends on the scale observed. The comparison of the strains at the mesoscopic and the macroscopic scales also highlights that their values depend on the study scale: the presence of cracks at the mesoscopic scale leads to a large overestimation of the values of the strains calculated at the macroscopic scale.In contrast to the observations in the laboratory, the desiccation cracks detected in the gallery systematically open when RH decreases. This difference and the differences observed in the geometrical organization of crack networks are explained by the different boundary conditions prevailing in both cases (i.e., free swelling/shrinkage in laboratory versus constrained swelling/shrinkage in the gallery).The interpretation of the entire dataset emphasizes the need for a multi-scale approach to understand and model desiccation cracking mechanisms and the associated hydric strains in clay rocks.

On the evolution of the elastic properties of organic-rich shale upon pyrolysis-induced thermal maturation

The evolution of the elastic properties of organic-rich shale as a function of thermal maturity remains poorly constrained. This understanding is pivotal to the characterization of source rocks and unconventional reservoirs. To better constrain the evolution of the elastic properties and microstructure of organic-rich shale, we have studied the acoustic velocities and elastic anisotropy of samples from two microstructurally different organic-rich shales before and after pyrolysis-induced thermal maturation. To more physically imitate in situ thermal maturation, we performed the pyrolysis experiments on intact core plugs under applied reservoir-magnitude confining pressures. Iterative characterization of the elastic properties of a clay-rich, laminar Barnett Shale sample documents the development of subparallel to bedding cracks by an increase in velocity sensitivity to pressure perpendicular to the bedding. These cracks, however, are not visible through time-lapse scanning electron microscope imaging, indicating either submicrometer crack apertures or predominant development within the core of the sample. At elevated confining pressures, in the absence of pore pressure, these induced cracks close, at which point, the sample is acoustically indistinguishable from the prepyrolysis sample. Conversely, a micritic Green River sample does not exhibit the formation of aligned compliant features. Rather, the sample exhibits a largely directionally independent decrease in velocity as load-bearing, pore-filling kerogen is removed from the sample. Due to the weak alignment of minerals, there is comparatively little intrinsic anisotropy; further, due to the relatively directionally independent evolution of velocity, the evolution of the anisotropy as a function of thermal maturity is not indicative of aligned compliant features. Our results have indicated that horizons of greater thermal maturity may be acoustically detectable in situ through increases in the elastic anisotropy of laminar shales or decreases in the acoustic velocities of nonlaminar shales, micritic rocks, or siltstones.

Coseismic extension from surface cracks reopened by the 2014 Pisagua, northern Chile, earthquake sequence

The A.D. 2014 Pisagua earthquake sequence reactivated ancient surface cracks along the entire rupture length in the northern Chilean forearc. These subtle brittle strain features that are ∼50 km above the subduction zone interface in the hyperarid Atacama Desert record deformation from the single earthquake sequence. In this study we document how ancient cracks, formed during thousands of plate boundary earthquake cycles, were reopened during the 2014 earthquake sequence. We show that crack orientations along the rupture length reflect deformation from the M w 8.1 mainshock and from an M w 7.7 aftershock 100 km to the south, as documented by displacements calculated from continuous geodetic observations. We suggest that cracks form during the passage of surface waves, and repeated opening and closing enhance crack aperture. The orientation and opening of the oldest cracks in the forearc are indicative of the modal or most common rupture area of major megathrust earthquakes in the region. While the long-term preservation of cracks may be limited to northern Chile, similar features likely form during strong earthquakes at other subduction zones and represent permanent forearc deformation.

Verification of a simulation approach for estimating crack aperture using <SUP>14</SUP>C-PMMA method

Verification of a simulation approach for estimating crack aperture using <SUP>14</SUP>C-PMMA method

Microstructural evolution in bitaxial crack‐seal veins: A phase‐field study

AbstractBitaxial crack sealing by epitaxial crystal growth is the most common vein‐forming process in Earth's crust, but the details of the microstructural processes in these are not well understood. Here we model the evolution of bitaxial crack‐seal quartz veins in two and three dimensions, using the phase‐field method. Our numerical simulations show the influence of different parameters, such as the obliquity of crack opening and crack location, grain size, and orientations on the evolving vein microstructure. We examine the underlying growth competition observed during epitaxial growth of quartz. Results show many similarities with natural microstructures such as stretched crystals and compare well with the previous numerical findings. As the ratio of crack aperture and matrix grain size for the present studies is chosen to be sufficiently large for growth competition to occur before complete sealing, it leads to the formation of crystal fragments along the crack‐opening trajectory. We explain how such fragment trails act as potential indicators of the opening of crack‐seal veins, if they are confirmed to be common in natural microstructures. Finally, we highlight the importance of accounting for the third dimension in the numerical simulations by analyzing the evolution of fluid connectivity in 2‐D and 3‐D during the sealing process.