Brittle Rock Failure Research Articles

Investigating the Relationship between the Brittleness Index and Crack Initiation Stress for the Granite under Triaxial Compression

The brittle failure of rock is closely related to the rock crack initiation, propagation, coalescences and nucleation. Although many brittleness indexes have been proposed to describe the brittle behavior of rocks, the relationship between the brittleness index and crack initiation stress under triaxial compressive states has not been fully understood. This paper introduced the current main brittleness indexes and discussed their applicabilities for triaxial compressive tests. Granite specimens from a gold mine are prepared for experimental tests. The triaxial compressive tests are carried out on stiff testing machine and the confining pressures are 5 to 110 MPa. Experimental results on the stress-strain curves show that the post-peak behaviors of the granite under confining pressures are in Class I and Class II types. The brittleness indexes, crack initiation stress, compressive strength, elastic moduls and Poisson’s ratio of the granite are obtained and discussed. It has been found that, the crack initiation stress linearly increases with the increasing of confining pressure. Moreover, a power function can describe the relationship between the brittleness index and crack initiation stress for Class I rock behavior while an exponential function can describe the relationship between the brittleness index and crack initiation stress for Class II rock behavior.

Experimental Study on Mechanical Properties of Deep Buried Granite under Different Confining Pressures

Brittle failure of hard rock poses a serious threat to the stability of surrounding rock in deep underground engineering. In order to study the deformation and failure characteristics of deep buried granite under high confining pressure cyclic loading and unloading, MTS815 electro‐hydraulic servo rock test system was used to conduct cyclic loading and unloading tests under confining pressures of 15 MPa, 35 MPa, 45 MPa, and 55 MPa, and the corresponding stress‐strain curves and deformation failure characteristic curves were obtained. The experimental results show the follows: (1) under the same confining pressure, the peak strength, crack initiation stress, crack damage stress, and Poisson’s ratio of the specimens under cyclic loading and unloading are larger than those under conventional triaxial loading and unloading, and the unloading elastic modulus is smaller than that, under conventional triaxial compression; (2) the results show that, under different confining pressures, the granite samples show obvious brittle failure characteristics, the elastic modulus and crack initiation stress increase first and then decrease with the confining pressure, the peak strength and crack damage stress of the samples increase linearly with the confining pressure, and Poisson’s ratio increases first and then remains unchanged with the confining pressure; (3) under the two kinds of stress conditions, the macroscopic failure of the samples is mainly shear failure. The deformation and failure law of granite samples revealed in this study has significant reference value for the selection of rock mass mechanical model of surrounding rock stability of underground engineering, the formulation of surrounding rock support countermeasures, and the evolution law of mechanical parameters with damage variables.

Modeling time-dependent deformation behavior of brittle rock using grain-based stress corrosion method

This research presents a grain-based stress corrosion model to simulate time-dependent failure of brittle rock. Time-dependent deformation of rock is considered as the manifestation of stress corrosion that may occur inside grains and on grain boundaries. A damage-rate law is adopted and modified to describe continuous degradations of parallel-bond diameters and contact properties in the stress corrosion process. A detailed numerical scheme with self-adaptive determination of time step is used to simulate the time-dependent deformation behavior of rock. The results show that both the short-term mechanical properties and the fatigue test results of Lac du Bonnet granite can be reproduced by the proposed method. In addition, compared with the original parallel-bond stress corrosion method, the modified grain-based stress corrosion method predicts the failure time of rock better under low driving-stress ratios. With the increase of the driving-stress ratio, the failure time of the numerical specimen decreases, and the creep curves tend to have a stair-stepping shape. The numerical simulation results show that an increase of 15 MPa confining pressure under a driving-stress ratio of 0.6 can lengthen the failure time of the rock from 139 days to 11 years.

The Role of Load Control Modes in Determination of Mechanical Properties of Granite

Circumferential strain-control tests were suggested to obtain the complete stress–strain curves (SSCs) of intact rock. However, compression test performed by the axial strain-control loading is mostly used to obtain the strength parameters and the SSCs. The influences of load control modes on the mechanical behavior of rock have not been fully investigated and understood. In this study, triaxial compression tests are conducted on granite specimens loaded by using both axial strain-control and circumferential strain-control modes to examine influences of load control modes on the determined mechanical properties. The occurrence mechanism and influencing factors of class II behavior are studied, and the potential application of the class II SSC in the evaluation of brittle failure of hard rock is also discussed. Results show that the peak strength, elastic modulus and fracture angle are generally higher in the axial strain-control test than in the circumferential strain-control test, and the failure in the former is also more violent than the latter under the same confining pressure. The much lower and constant circumferential deformation rate applied in the circumferential strain-control test is the dominant factor that favors the recovery of the complete post-peak SSC. The lower measured values of strength and elastic modulus are also associated with the lower deformation rate in the circumferential strain-control test, with a higher degree of damage and cohesion weakening occurring inside the rock. The development of the class II SSC is attributed to the axial strain recovery during the release of the stored elastic energy, which is influenced by the ratio of elastic energy to dissipated energy in the pre-peak stage, and is also associated with the consumed energy with respect to plastic deformation or initiation and propagation of new cracks in the post-peak stage. The class II SSC can aid the differentiation of the energy accumulation and consumption of different brittle rocks, which are usually characterized by a more abrupt and larger stress drop in the axial strain-control test. It can then be used to evaluate the strain rockburst potential of a particular rock type.

Hardening–Softening Constitutive Model of Hard Brittle Rocks Considering Dilatant Effects and Safety Evaluation Index

The damage and even failure of hard brittle rocks has been the most important challenge facing the safety of construction of deep engineering works, so the key to solving this problem is the recognition of the strength characteristics and description of the mechanical behavior of hard brittle rocks. Therefore, in view of this problem, in this study, we first analyzed the strength and mechanical response characteristics revealed in tests of, and site excavation in, hard brittle rocks. Second, by analyzing rock-strength envelopes on meridional and deviatoric planes, the generalized polyaxial strain energy (GPSE) strength criterion was applied. This allows description of the effects of the minimum principal stress, intermediate principal stress, hydrostatic pressure, and Lode’s angle of stress on the strength of hard rocks. By establishing evolutionary relationships of strength parameters and dilation parameters with plastic volumetric strain in rock failure, we established an elasto-plastic mechanical constitutive model for hard brittle rocks based on the GPSE criterion. In addition, through use of the failure approach index theory and the dilatancy safety factor, an evaluation index for degree of damage considering dilatant effects of rocks was proposed. Finally, the constitutive model established in this study and the proposed evaluation index were integrated into the numerical simulation method to simulate triaxial tests on rocks and numerical simulation of deformation and fracture of the rocks surrounding the deep-buried auxiliary tunnels in China’s Jinping II Hydropower Station. In this way, the reasonableness of the model and the index was verified. The strength theory and the constitutive model established in this research are applicable to the analysis of high-stress deformation and fracture of hard brittle rock masses, which supports the theoretical work related to deep engineering operations.

A stochastic rupture earthquake code based on the fiber bundle model (TREMOL v0.1): application to Mexican subduction earthquakes

Abstract. In general terms, earthquakes are the result of brittle failure within the heterogeneous crust of the Earth. However, the rupture process of a heterogeneous material is a complex physical problem that is difficult to model deterministically due to numerous parameters and physical conditions, which are largely unknown. Considering the variability within the parameterization, it is necessary to analyze earthquakes by means of different approaches. Computational physics may offer alternative ways to study brittle rock failure by generating synthetic seismic data based on physical and statistical models and through the use of only few free parameters. The fiber bundle model (FBM) is a stochastic discrete model of material failure, which is able to describe complex rupture processes in heterogeneous materials. In this article, we present a computer code called the stochasTic Rupture Earthquake MOdeL, TREMOL. This code is based on the principle of the FBM to investigate the rupture process of asperities on the earthquake rupture surface. In order to validate TREMOL, we carried out a parametric study to identify the best parameter configuration while minimizing computational efforts. As test cases, we applied the final configuration to 10 Mexican subduction zone earthquakes in order to compare the synthetic results by TREMOL with seismological observations. According to our results, TREMOL is able to model the rupture of an asperity that is essentially defined by two basic dimensions: (1) the size of the fault plane and (2) the size of the maximum asperity within the fault plane. Based on these data and few additional parameters, TREMOL is able to generate numerous earthquakes as well as a maximum magnitude for different scenarios within a reasonable error range. The simulated earthquake magnitudes are of the same order as the real earthquakes. Thus, TREMOL can be used to analyze the behavior of a single asperity or a group of asperities since TREMOL considers the maximum magnitude occurring on a fault plane as a function of the size of the asperity. TREMOL is a simple and flexible model that allows its users to investigate the role of the initial stress configuration and the dimensions and material properties of seismic asperities. Although various assumptions and simplifications are included in the model, we show that TREMOL can be a powerful tool to deliver promising new insights into earthquake rupture processes.

Triaxial Loading and Unloading Tests on Dry and Saturated Sandstone Specimens

The brittle failure of hard rock due to the excavation unloading in deep rock engineering often causes serious problems in mining and tunneling engineering, and the failure process is always affected by groundwater. In order to investigate the effects of stress paths and water conditions on the mechanical properties and failure behavior of rocks, a series of triaxial compression tests were conducted on dry and saturated sandstones under various loading and unloading paths. It was found that when the sandstone rock samples are saturated by water, the cohesion, the internal friction angle and the Young’s modulus will decrease but the Poisson′s ratio will increase. The fracturing characteristics of the sandstone specimens are related to the initial confining pressure, the stress paths and the water conditions from both macroscopic and microscopic viewpoints. The failure of sandstone in unloading test is more severe than that under loading test, particularly for dry sandstone samples. In unloading test, the energy is mainly consumed for the circumferential deformation and converted into kinetic energy for the rock bursts. The sandstone is more prone to produce internal cracks under the effect of water, and the absorbed energy mainly contributes to the damage of rock. It indicates that the possibility of rockburst in saturated rock is lower than the samples in dry condition. It is important to mention that water injection in rock is an effective way to prevent rockburst in deep rock engineering.

Progressive failure of brittle rocks with non‐isometric flaws: Insights from acousto‐optic‐mechanical (AOM) data

AbstractUniaxial compression tests combined with nondestructive testing techniques are performed to explore the roles of non‐isometric flaws in crack developments in brittle rocks. The acoustic emission (AE) rate‐process theory is adopted to analyze fracture‐related AE event rate characteristics. The full‐field optical method is applied to detect cracking modes. Experimental results show that AE activity is quite active when the matrix microcracking is dominant, while after each macrocracking event, AE activity becomes inactive because of the stress release. Multiphysical data for each tested flaw configuration faithfully confirm the rupture progressivity. The larger the flaw length ratio, the lower the peak stress (also peak axial strain and elastic modulus), as well as the more progressive the cracking process. Moreover, ultimate failure is triggered by the shear fracturing from the relatively long flaw. The short flaw is conditionally involved in ultimate failure when the stress buildup effect dominates. Finally, the fracture mechanism of brittle rocks with non‐isometric flaws is revealed.

Strainburst phenomena and numerical simulation of self-initiated brittle rock failure

This paper focuses on ‘self-initiated’ strainbursts, and starts by providing an overview of these phenomena and their relevance to mining. This is used to set the framework for the numerical simulations presented in the second part of the paper. The numerical simulations examine and address challenges in modelling strainbursts related to the inherent difficulties in dynamic failure simulation. Existing methods either simulate dynamic failure under static or pseudo-static conditions while adopting some threshold factor (normally in terms of stress, strain, or energy) as an indicator of rockburst potential, or incorporate an assumed dynamic disturbance to cause rockburst damage. A distinct-element bonded block method is presented to simulate strainbursts. Instead of triggering failure by an assumed dynamic disturbance, the adopted method simulates the generation of a seismic event by self-initiated rock mass fracturing. This simulation of a self-initiated strainburst is interpreted using patterns of cracking, displacement and strain fields, ground velocities, and calculated kinetic and dissipated slip energies. The mechanisms of self-initiated strainbursting are successfully captured by the distinct-element bonded block method.

Novel grain-based model for simulation of brittle failure of Alxa porphyritic granite

A grain-based model (GBM) is generally employed by many researchers to simulate the microcracking process of crystalline brittle rock by the distinct element method. In this study, a novel grain-based model (nGBM) in two-dimensional Particle Flow Code 5.0 (PFC2D 5.0) is proposed to emulate the brittle failure of crystalline rock. First, the nGBM scheme is introduced, in which the flat-joint model is employed to model the contacts in mineral grains and the smooth-joint model is assigned to the grain interface contacts. Then, compressive tests are performed using Alxa porphyritic granite, and the strength values are fitted with the Hoek-Brown failure criterion. Third, a nGBM was generated based on the petrographic texture of realistic rock, such as mineral constituents, grain size, and distribution. The input microscale parameters are carefully calibrated according the experimental results. Finally, this model is applied to study the microcracking process of Alxa porphyritic granite and the influence of spatial distribution of minerals. It is found that a relatively high ratio of uniaxial compressive strength to tensile strength of each mineral or synthetic samples can be reproduced by the nGBM. Moreover, the simulated results show this model can capture the nonlinear characteristic of the Hoek-Brown failure criterion. After modeling, numerous mineral grains were cut across, which is consistent with the actual experimental observation; the tensile crack is over the shear crack in the models, while the number of intra-grain shear crack increases dramatically with increasing confining pressure. In addition, the numerical results indicate that the effect of spatial distribution of minerals has limited influence on the evolution of microcracks but has great impact on microcrack distribution. In summary, the proposed nGBM in PFC2D can well reproduce the realistic failure process of granitic rocks under different loading conditions.

Numerical Simulation for the Dynamic Breakout of a Borehole Using Boundary Element Method

Borehole breakouts are formed by spalling of fragments in a direction parallel to the least horizontal stress. As the breakouts falling into the wellbore or being scoured by the drilling mud piece by piece, the stress concentration on the wellbore will release gradually. The wellbore is not circular or elliptical, which requires a numerical method to determine the redistributed stress around the irregular borehole. In this article, boundary element method associated with the brittle rock failure criterion is deployed to simulate the dynamic breakout of a borehole. The borehole shape is updated step by step during the time-dependent breakout. The first breakout volume is smaller than the analytical solution (Gholami et al. in J Rock Mech Geotech Eng 8:521–532, 2016). However, the total breakout volume is larger than the analytical solution because our model considers the subsequent failure of the irregular wellbore. The stress distribution around the irregular wellbore after each step of breakout is investigated and the maximum cohesive strength at which the rock will fail is figured out. These results provide new insights to understand the dynamic process of borehole breakout.

The specificities of deformations and failures of highly stressed hard rock massifs

According to modern concepts, the state of highly stressed hard rock massifs is mostly caused by the effect of gravitational-tectonic stress fields. At that, a probability of brittle rock failure in a dynamic form is very high. Such failures are always accompanied by the significant energy release accumulated during the deformation process. Based on the experimental studies of deformation and failure processes in various types of rock samples from the Kola Peninsula deposits, we have proposed the criteria for classifying rocks as prone to rock bursts. The information for assessing the rock proneness to dynamic failures can be obtained by analysing the strain curve at the pre-peak section when tested on the ordinary presses and testing devices according to the standard methods. If we study the processes of rocks' deformation and energy accumulation under the triaxial loading mode, we can establish the parameters for the occurrence of dynamic failure of rocks. This, in turn, will allow identifying the conditions of such failure in the investigated rocks for a specific mining-engineering situation and, thereby, coming to a scientifically-based prediction of the rocks' proneness to dynamic rock pressure occurrences.

A unified analytical method calculating brittle rocks deformation induced by crack growth

An improved unified method is proposed to calculate the relations of stress to axial, lateral, and volumetric strains, involving the short-term progressive failure and long-term creep of brittle rocks. In the present paper, wing crack model, subcritical crack growth law and a crack-strain criterion for brittle rocks are coupled to formulate the frame of the proposed method. The limitation of the crack growth at crack coalescence is discussed as well, and the effects of confining pressure on relations between axial, lateral and volumetric strains and axial stress during progressive failure are analyzed, then the corresponding stress-strain curve during multi-loading creep is obtained. These theoretical derivations and calculation agree well with the previous experimental results, the proposed unified method is validated and can be applied into calculate brittle rocks deformation induced by crack growth.

Acoustic Emission Associated with Self-Sustaining Failure in Low-Porosity Sandstone Under Uniaxial Compression

Two sets of uniaxial compression tests were conducted on a brittle sandstone under a constant circumferential strain rate (2 × 10−6 s−1) and a constant axial strain rate (2.5 × 10−6 s−1), respectively. A combination of active and passive ultrasonic techniques was implemented to study the effect of the control method on mechanical deformation, ultrasonic P-wave velocity, acoustic emission (AE) characteristics, and the ultrasonic amplitude spectrum. During each test, active surveys were performed at regular time intervals. P-wave velocity was found to be strongly anisotropic and was used for the construction of a time-dependent transversely isotropic velocity model for each specimen. AE data were continuously acquired and digitized at 10 MHz and 16-bits for the duration of each test where four channels were amplified 30 dB and the rest 50 dB. Discrete AE events were harvested from the continuous waveforms and were then used for source location analysis based on the constructed velocity model and the collapsing grid search routine. An analysis of the ultrasonic amplitude spectrum was also performed to relate attenuation to the formation of macroscopic fracture. In addition, the post-peak energy balance was quantitatively estimated by calculating the rupture energy, surplus energy, and residual elastic energy, suggesting a typical self-sustaining failure. Differences in the post-peak energy balance between the two sets of tests are also reflected in the AE magnitude distribution in addition to the failure modes. Finally, the reason for the large amount of missing AE data associated with eventual rupture was investigated, with the conclusion that multiple gain levels should be adopted during brittle failure of rocks.

Unloading-induced failure of brittle rock and implications for excavation-induced strain burst

Understanding the unloading-induced failure characteristics of brittle rock is essential for predicting excavation-induced strain burst. We conduct both the laboratory experiments and discrete element simulations to investigate the deformation, failure pattern, and strain energy evolution of the Bukit Timah granite. The laboratory tests with radial unloading show that the radial strain mainly contributes to the change of volumetric strain in the unloading process. The numerical tests with the flat-jointed contact model reproduce the Hoke-Brown failure envelope of the rock, and simulate the unloading-induced rock failure under different combinations of initial confining pressure and unloading rate. The evolutions of strain energy release and failure pattern show that higher unloading rate likely induces violent failure, in terms of greater lateral expansion and more ejected fragments. The micromechanical analyses on the particle velocity and tensile contact force reveal that the non-uniform rock deformation concentrates at lateral surfaces and results in strain burst with fragment ejection. The Hoek-Brown failure criterion well predicts the confining pressure at failure when the rock is laterally unloaded at lower unloading rate, but likely overestimates the stress level at higher unloading rate.

Failure pattern of brittle rock governed by initial microcrack characteristics

Fracturing processes of rock are simulated using a micro- and fracture mechanical-based numerical modeling approach. The numerical model considers material heterogeneity and initial microcrack distributions. The gradual formation of macroscopic fractures by coalesced microcracks is successfully reproduced. Distinct failure modes are observed in the model under different loadings. Agreement is shown between the numerical results and laboratory observations. The influence of microcrack orientations on the fracture patterns is quantified by the numerical models. Possible mechanisms describing the splitting failure of hard brittle rocks under uniaxial compression are proposed and discussed.

A temperature- and stress-controlled failure criterion for ice-filled permafrost rock joints

Abstract. Instability and failure of high mountain rock slopes have significantly increased since the 1990s coincident with climatic warming and are expected to rise further. Most of the observed failures in permafrost-affected rock walls are likely triggered by the mechanical destabilisation of warming bedrock permafrost including ice-filled joints. The failure of ice-filled rock joints has only been observed in a small number of experiments, often using concrete as a rock analogue. Here, we present a systematic study of the brittle shear failure of ice and rock–ice interfaces, simulating the accelerating phase of rock slope failure. For this, we performed 141 shearing experiments with rock–ice–rock “sandwich”' samples at constant strain rates (10−3 s−1) provoking ice fracturing, under normal stress conditions ranging from 100 to 800 kPa, representing 4–30 m of rock overburden, and at temperatures from −10 to −0.5 ∘C, typical for recent observed rock slope failures in alpine permafrost. To create close to natural but reproducible conditions, limestone sample surfaces were ground to international rock mechanical standard roughness. Acoustic emission (AE) was successfully applied to describe the fracturing behaviour, anticipating rock–ice failure as all failures are predated by an AE hit increase with peaks immediately prior to failure. We demonstrate that both the warming and unloading (i.e. reduced overburden) of ice-filled rock joints lead to a significant drop in shear resistance. With a temperature increase from −10 to −0.5 ∘C, the shear stress at failure reduces by 64 %–78 % for normal stresses of 100–400 kPa. At a given temperature, the shear resistance of rock–ice interfaces decreases with decreasing normal stress. This can lead to a self-enforced rock slope failure propagation: as soon as a first slab has detached, further slabs become unstable through progressive thermal propagation and possibly even faster by unloading. Here, we introduce a new Mohr–Coulomb failure criterion for ice-filled rock joints that is valid for joint surfaces, which we assume similar for all rock types, and which applies to temperatures from −8 to −0.5 ∘C and normal stresses from 100 to 400 kPa. It contains temperature-dependent friction and cohesion, which decrease by 12 % ∘C−1 and 10 % ∘C−1 respectively due to warming and it applies to temperature and stress conditions of more than 90 % of the recently documented accelerating failure phases in permafrost rock walls.

Dilatancy as a measure of fracturing development in the process of rock damage

Abstract Dilatancy understood as inelastic volume changes of rock under conditions of differential stress not only foreshadows brittle rock failure [1, 2, 3], preceding such phenomena as earthquakes or mining-induced rockbursts, but also defines the kinematics of rock deformation [4, 5]. This article shows that there is a quantitative relationship between the dilatancy occurring at different levels of rock load and the development of fracturing that accompanies the process of rock degradation. Based on the mechanical laboratory test results of Wustenzelleer fine-grained sandstone, the article presents analyses of plastic volume changes in rock samples and a certain measure of fracture development accompanying the process of their degradation. Thanks to the characteristics obtained through mechanical tests with unloading, the inelastic volumetric strain of the samples was established, and the scalar damage variable (CDM - continuum damage mechanics approach) was determined at various load levels. These results demonstrated the relationship between dilatancy and rock stiffness changes describing the development of fracturing. Three load intervals were determined, in which the nature of the analysed phenomena, i.e. dilatancy and damage describing the development of cracks, undergoes significant changes. The highest intensity of both phenomena was obtained in the post-critical load range, between the ultimate strength limit and the residual strength of the samples, in which rock samples undergo the process of degradation the most. Obtained dependencies allow the correlation to be taken into account in damage mechanics models describing the variable stiffness of rocks in the loading process.

Modeling of brittle rock failure considering inter- and intra-grain contact failures

Based on a two-scale tessellation technique in Neper, a 3DEC-GBM modeling approach considering inter- and intra-grain contact failures is proposed to study brittle rock failure. Plane strain problems are solved using 3DEC to reduce computation time. A parametric study of inter- and intra-grain contact properties is conducted and a calibration procedure is suggested for determining micro-mechanical properties of granular materials. The modeling results indicate that inter- and intra-grain contact strength heterogeneity affects not only the peak strength of rock but also the microcrack spatial location and hence the fracture development path and fracture pattern.

A Quantitative Strain Energy Indicator for Predicting the Failure of Laboratory-Scale Rock Samples: Application to Shale Rock

Strain energy is one of the key factors that control the brittle failure process of rock mass, such as the onset of accelerating displacement. The phenomenon of accelerating displacement is a necessary and important precursor to predict the brittle failure of rock, and it is attributed to the unstable propagation of micro-cracks when the load reaches or exceeds the crack damage stress threshold. Thus, for the design of underground rock engineering and to ensure proper safety practices, it is important to propose a suitable strain energy criterion that uses the strain energy at the crack damage stress threshold (Wcd) to predict the strain energy at final failure (Wucs). For this purpose, a quantitative strain energy indicator (Wucs/Wcd) was proposed based on two-dimensional renormalization group theory for the prediction of the brittle failure of laboratory-scale rock samples subjected to uniaxial pressure. The indicator is a function of the homogeneity index, m, of the Weibull distribution. The reliability of the strain energy indicator was verified by a series of uniaxial compression tests on 12 shale samples that had different homogeneity indices, m. The heterogeneity of the sample was dominated by different bedding dip angles. The experimental results showed that the quantitative indicator could be used to predict the brittle failure of samples of any type of rock at the laboratory scale using their m values. In addition, the effect of the bedding dip angle on the homogeneity index, m, and the strain energy indicator were discussed based on the experimental results to provide a better understanding of the relationships among heterogeneity, the strain energy indicator, and the other physical and mechanical properties of the shale samples that were tested. Also, the discussion included the effects of the homogeneity of the sample and the strain energy indicator on the physical and mechanical properties of the samples. As a result, some conclusions were obtained that might be applicable to laboratory-scale shale samples.