Failure Mechanism Of Rock Research Articles

Influence of groundwater on micro-cracking behaviour and failure mechanism of deep hard rock

To address the water-inrush hazards encountered in deep tunnels in the rugged terrain of Southwest China, the uniaxial compression tests and acoustic emission (AE) monitoring were conducted on granite samples taken from a deep tunnel with different durations of saturation (2 days and 30 days), and the results were compared with those of natural granite samples. The results revealed the influence of groundwater on the mechanical properties, micro-cracking behavior, and failure modes of granite, which provided guidance for the deep tunnel construction. Based on the previous work, an optimized method for extracting the dominant frequency of rock AE signals considering the effect of groundwater on hard granite was proposed, which corrected the inaccurate extraction problem in the traditional method. The optimally extracted high dominant frequency AE signals could also be used as a precursor of rock failure.

Uncertainty of microseismic sources identification and probabilistic location in underground excavation

Microseismic (MS) source location is an integral component of MS technology and essential to understanding the rock failure mechanism and avoiding potential geological hazards in underground rock excavation. However, accurate location remains challenging owing to the complex geological conditions and unknown rock failure mechanisms. In this study, a novel location framework was developed to locate the MS source positions and their uncertainties based on probabilistic programming. Probabilistic programming was utilized to determine the coordinates of the MS source and its variation using the Markov Chain Monte Carlo (MCMC) method based on the waveform equation. A classical benchmark problem was utilized to verify and illustrate the developed framework. The developed framework can not only locate the position of the MS source but also determine its variation due to the uncertainty during the monitoring and excavation. The located MS source is in agreement with the actual positions. The results show that the developed framework is a scientific, accurate, reasonable, and promising tool for the location of MS sources. Then, the developed framework was applied to locate the position of the blasting in a practical mine. This further proved that the developed framework could locate the MS source, providing an excellent uncertainty analysis tool for underground rock excavation.

Mechanical behavior evolution and failure characteristics of saturated and dry rocks under different water pressure environments

A complex and changeable water environment is a key factor for safe rock engineering. Variations in water distribution and pressure pose serious challenges in evaluating rock properties and failure modes. To investigate the effect of real water‒rock interactions on rock mechanical behavior, the self-developed hydraulic loading test equipment was designed. A series of mechanical experiments (unjacketed) were carried out on three representative types of rocks under different water pressure environments, and the jacketed test was also performed for the saturated rocks. The experimental results showed that with increasing water confining pressure, the stress‒strain curve of the saturated rocks increased, while that of the dry rocks first decreased and then increased, and that of the sandstone became more obvious. Furthermore, when the water confining pressure increased, the peak stress and elastic modulus of the saturated rocks increased linearly, and those of the dry rocks first decreased and then increased more sharply. Interestingly, the water confining pressure weakened the local tensile failure and aggravated the shear failure. The relationship between the water confining pressure and strength also indicated that the change of saturated rocks more slowly when in contact with the water confining pressure. From the above results, the pore water pressure correction coefficients (μ) of sandstone, marble and granite were 0.98, 0.96 and 0.93, respectively, in the water pressure environment and rock connection. The failure mechanism of saturated rocks is similar to that of rocks without confining pressure due to the balance of the water confining pressure and pore water pressure, and pore water pressure mainly acts as piestic water. For dry rocks, the penetration of pore water firstly weakens the mechanical properties of rocks when pore water pressure is smaller. A greater confining pressure enhances the role of traditional confining pressure for granite and dry rocks.

Experimental investigation into grain size effect on failure behavior and nonlinear time-varying acoustic emission series of granite

This study aims to investigate the grain size effect on mechanical properties and failure mechanisms of hard rock. Thus, a series of uniaxial compression experiments were carried out on granites with various grain sizes, and acoustic emission (AE) signals were synchronously collected in the experimental process for further nonlinear analysis. The results show that the four characteristic stresses of granite (σcc, σci, σcd, and σc) significantly decrease with the increase of grain size. The ratio of σcd/σc basically remains a constant of 0.8; the ratio of σci/σc increases gradually from 0.6 to about 0.7; the ratio of σcc/σc also shows a rising trend overall. With the increase of grain size, the AE energy level rises; the proportion of high-frequency tensile signals is reduced; the multi-fractal parameters Δα (non-uniformity of signals) and Δf (frequency difference between minimum and maximum signals) decrease. During the loading process, the time-varying value of Δα changes between 0.0 and 0.35, and that of Δf changes within the range from −0.2 to 0.5, showing a ‘rise-fall-rise-fall’ mode. The grain size effect on the influence of crack evolution is further discussed based on the nonlinear time-varying AE analysis. All these results reflect the mechanisms of grain size effect on granite. Large grain size weakens grain boundaries, facilitating shear slip along weak planes between crystal particles. In addition, the enhanced local stress concentration and initial defects in rock with large grain size could activate the crack coalescences of intra-crystalline cracks and weak boundary planes more easily in a relatively low-stress state.

Seismic and radon signatures: A multiparametric approach to monitor surface dynamics of a hazardous 2021 rock–ice avalanche, Chamoli Himalaya

AbstractThe observation of precursory signals of the 2021 Chamoli rock–ice avalanche provides an opportunity to investigate the multidisciplinary analysis approach of rock failure. On 7 February 2021, a huge rock–ice mass detached from the Raunthi peak at Chamoli district in Uttarakhand, India. The tragic catastrophe resulted in more than 200 deaths and significant economic losses. Here, we analyse radon concentration and seismic signals to characterise the potential precursory anomalies prior to the detachment. Continuous peaks of radon anomalies were observed from the afternoon of 5 to 7 February and decreased suddenly after the event, while a cumulative number of seismic tremors and amplitude variations are more intensified ~2.30 h before the main event, indicating a static to dynamic phase change within the weak zone. This study not only characterises abnormal signals but also models the rock failure mechanisms. The analysis unveils three time‐dependent nucleation phases, physical mechanisms of signal generation and a complete scenario of physical factors that affected the degree of criticality of slope failure. The results of this study suggest gradual progression of rock cracks/joints, subsequent material creep and slip advancement acceleration preceded the final failure. Furthermore, the study highlights the importance of an early warning system to mitigate the impact of events like the 2021 Chamoli rock–ice avalanche.

Effect of regionalized structures on rock fracture process

The structure of rocks plays a crucial role in their failure process. However, it is ignored that the interactions between rock internal structure and the effect of its own evolution on the rock fracture process. To investigate the effect between the evolution law of rock regionalized structures and their interaction relationships during failure. We conducted an experiment using visual acoustic imaging monitoring to study rock failure, introducing a new concept of characteristics of rock structure—regionalized structures. The findings reveal three main types of regionalized structures in rocks: skeleton regions, variable regions, and damage regions. These structures combine to form four categories of complex rock structures: block-type support skeletons, point column-type support skeletons, suspension-type weak support skeletons, and no skeletons. During the failure process, we found that these regionalized structures worked together synergistically to control rock failure. Although the evolutionary relationships among the structures show some similarities, the final fracture states vary significantly. Stress and strain distribution patterns clearly demonstrate that variations in the force capacities and roles of the regionalized structures influence the synergistic evolutionary relationships, ultimately impacting the mode of rock failure. This work provides new insights for further research on rock failure mechanisms and can significantly contribute to preventing rock engineering disasters related to regionalized structures.

The macroscopic and microscopic fatigue failure mechanisms of high-temperature thermally-damaged granite under cyclic impact loading

The rock surrounding wells for developing geothermal energy are in an extreme environment with high temperature and long-term dynamic disturbance. To study the influences of different temperatures and dynamic disturbances on the damage, mechanical properties, and fatigue failure mechanism of rocks, a series of microscopic thermal damage analysis and dynamic cyclic impact tests were conducted on granite specimens treated at 25 ∼ 900 °C. Results show that after being thermally treated to different extents, granite specimens are weakened in terms of the dynamic strength and deformation resistance under cyclic impact loading. As the temperature rises, the number of impacts bearable by specimens before failure decreases accordingly. Under the joint action of temperature and strain rate, 450 °C is found to be the threshold temperature for the significant reduction of dynamic strength of the rock. Under action of temperature and strain rate, the proportion of dissipated energy gradually reduces with rising temperature. Moreover, the dynamic failure mode of rock specimens at high temperatures gradually changes from splitting failure to crushing failure, the fractal dimension gradually increases, and the cumulative dissipated energy density decreases. Finally, the deterioration degree of elastic modulus was adopted to describe the progressive damage evolution of thermally-treated granite under cyclic impact loading. Furthermore, the fracture morphologies of rock specimens after failure were analyzed from the microscopic perspective to reveal the macroscopic and microscopic fatigue failure mechanisms of the rock under the coupling of temperature and strain rate.

Microscopic analysis of mechanical anisotropy and damage evolution of 3D printed rock-like samples under uniaxial compressive tests

Three-dimensional printing (3DP) offers valuable insight into the characterization of natural rocks and the verification of theoretical models due to its high reproducibility and accurate replication of complex defects such as cracks and pores. In this study, 3DP gypsum samples with different printing directions were subjected to a series of uniaxial compression tests with in situ micro-computed tomography (micro-CT) scanning to quantitatively investigate their mechanical anisotropic properties and damage evolution characteristics. Based on the two-dimensional (2D) CT images obtained at different scanning steps, a novel void ratio variable was derived using the mean value and variance of CT intensity. Additionally, a constitutive model was formulated incorporating the proposed damage variable, utilizing the void ratio variable. The crack evolution and crack morphology of 3DP gypsum samples were obtained and analyzed using the 3D models reconstructed from the CT images. The results indicate that 3DP gypsum samples exhibit mechanical anisotropic characteristics similar to those found in naturally sedimentary rocks. The mechanical anisotropy is attributed to the bedding planes formed between adjacent layers and pillar-like structures along the printing direction formed by CaSO4·2H2O crystals of needle-like morphology. The mean gray intensity of the voids has a positive linear relationship with the threshold value, while the CT variance and void ratio have concave and convex relationships, respectively. The constitutive model can effectively match the stress–strain curves obtained from uniaxial compression experiments. This study provides comprehensive explanations of the failure modes and anisotropic mechanisms of 3DP gypsum samples, which is important for characterizing and understanding the failure mechanism and microstructural evolution of 3DP rocks when modeling natural rock behavior.

Study on rock energy evolution and constitutive model under water–rock interaction

To explore the degradation in rock mechanical properties due to water–rock interactions and formulate a nonlinear damage constitutive model for the entire stress–strain curve of rocks, experiments involving saturated, dry-wet cycling, and uniaxial compression tests were conducted on granite and siltstone. Based on energy theory, the energy evolution of the rock throughout the testing process was scrutinized. The range of the compaction stage was identified through the analysis of the dissipation energy change curve. A nonlinear damage constitutive model for rocks subjected to water-rock interactions was then devised, drawing on concepts from statistical damage mechanics. The findings indicated a progressive reduction in uniaxial compressive strength and elastic modulus due to water–rock interactions, while the Poisson’s ratio was observed to increase. The energy density curve under these conditions delineated four distinct phases: compaction energy dissipation, linear energy accumulation, pre-peak gradient increase, and post-peak sudden change. The introduction of the unit elastic strain energy density metric underscored the deteriorating effects from an energy standpoint. A nonlinear damage constitutive model, incorporating the compaction stage based on a coupled damage variable, was formulated. The predictions of this model closely matched the empirical data, thereby affirming its validity. This model provides an enhanced depiction of rock deformation and failure mechanisms under the influence of water–rock interactions.

Creep Energy Evolution of Red-Bed Soft Rocks in South China under Chemical-Stress-Seepage Coupling

The red-bed soft rocks in South China have obvious creep characteristics and are prone to engineering geological disasters such as landslide and foundation settlement under the action of rainfall, groundwater, and load. In order to reveal its creep characteristics and mechanism under complex conditions, a step-loading creep test was carried out under chemical-stress-seepage coupling, and the energy evolution law of the whole creep process was analyzed based on linear energy storage and energy dissipation theory. The results also show that the acid chemical solution has the greatest influence on the triaxial strength and creep strength, and the creep damage and energy evolution of red-bed soft rock are universal. The creep damage and total strain increase with the increase of acidity, the decrease of confining pressure, and the increase of seepage pressure. The evolution law of creep damage shows the characteristics of slow-acceleration-rapid growth, and with the increase of load level, it has obvious transfer and accumulation. After entering the constant velocity creep stage, the damage rate begins to accelerate. The proportion of instantaneous strain and creep strain in the total strain increment is about 50%, and confining pressure has little influence on their respective proportions. The instantaneous strain is more sensitive to the acidity of the chemical solution, and the proportion of creep strain increases gradually with the increase of seepage pressure. The relationship between elastic energy density and total energy density is linear. The elastic energy density and dissipated energy density in the loading stage and creep stage all increase nonlinearly with loading time. The density of dissipated energy in the creep phase is lower than that in the loading phase, but the opposite is true in the higher stress phase, and the law of energy dissipation can explain the hardening damage effect in the creep process of soft rock samples. The research results provide a new perspective for us to reveal the mechanical properties and failure mechanism of red-bed soft rocks and provide an important theoretical basis for predicting and evaluating the creep instability and long-term stability of such rocks.

Investigation into the Failure Characteristics and Mechanism of Rock with Single Elliptical Defects under Ultrasonic Vibrations

In order to investigate the effects of elliptical defects on rock failure under ultrasonic vibrations, ultrasonic vibration tests and PFC2D numerical simulations were conducted on rocks with single elliptical defects. The research results indicated that the fracture fractal dimension, axial strain, and crack depth of specimens with elliptical defects at 45° and 90° were the smallest and largest, respectively. The corresponding strain and fractal dimension showed a positive linear and logarithmic function relationship with time. The maximum crack depth of 46.50 mm was observed on the specimens with an elliptical defect angle of 90°. Specimens with elliptical defects at 0°, 30°, 75°, and 90° exhibited more dense and frequent acoustic emission events than those with elliptical defects at 15°, 45°, and 60°. During the ultrasonic vibration process, the maximum total energy (87.86 kJ) and energy consumption coefficient (0.963) were observed on specimens with elliptical defect angles of 30° and 45°, respectively. The difference in the stress field led to varying degrees of plastic strain energy in the specimens, resulting in different forms of crack propagation and triggering differential acoustic emission events, ultimately leading to specimen failure with different crack shapes and depths. The fractal dimensions of elliptical defect specimens under ultrasonic vibration have a high degree of consistency with the changes in axial strain and failure depth, and the fractal dimension of defect specimens is positively correlated with the degree of failure of defect specimens.

The Influence of Rock Slope Scales of Joint Network and Slope Height on the Stability and Failure Mechanisms

This paper demonstrates the influence of slope geometry and scale of the joint networks on the stability and failure mechanisms in discontinued rock masses. These analyses are based on the finite element method (FEM) to calculate the factor of safety (FOS) and to simulate the explicit discontinuity deformations for different scales of rock masses. The study was carried out through examples of regular jointed models having different slope heights and irregular jointed dry rock slopes. Joints usually decrease the strength of the slopes and suggestively increase slope stability problems. The result shows that the slope stability decreases with increased block size and shape and that the irregular columnar joints are more unfavorable to the slope stability than the regular joints. Furthermore, with dropping the factor of safety and randomly distributed joints the rock failure mechanism appears to shift from structurally controlled for the 50 m slopes towards a step-like failure path for the 100 m and 200 m slopes.

Three-dimensional numerical simulation on failure mechanical characteristics of fissured sandstone specimens under true triaxial conditions

Understanding intermediate principal stress influences on deformation characteristics and failure mechanism of fractured rock from deep engineering often necessitates long term on-site detection and complex experimental research, although very limited efficacy can be obtained. With presently available experimental data on conventional triaxial cuboid noncoplanar fissured sandstones, this study further investigated the effects of differential stress (σ2 − σ3) and rock bridge inclination angle (β30°, β60°, β90°, β120°, and β150°) on their damage evolution processes and failure modes based on 3D discrete element methods (PFC3D). Numerical simulation results indicated that the peak strength of the fissured sandstone under the same state of horizontal principal stress shows an overall increasing pattern with the increase of the inclination angle of the rock bridge, while its peak strain displays a decreasing and then increasing trend. Besides, in this work, five failure modes, nine crack types and two kinds of stress–strain curves are summarized which are significantly affected by the horizontal principal stress, rock bridge inclinations or cooperative interaction. Differential stress value of 15 MPa is an important threshold for determining the residual strength of the stress–strain curve from present to absent. The cracking and force chain evolution processes of five failure modes were analyzed in order to discover the corresponding failure mechanisms. Finally, differential stress and flaw inclination influences on rock mechanical parameters and failure behavior have significant implications for strategies of the design, operation, and maintenance of rock engineering under severe conditions in the underground.

Experimental and numerical study on the dynamic mode III fracture behaviors of rock using an axially notched flattened Brazilian disc in SHPB tests

The dynamic mode I and mode II fracture of rock have been widely investigated over the past decades. However, the lack of dynamic mode III fracture testing method and the rare understanding of mode III fracture mechanism of rock remain a significant knowledge gap in the realm of rock mechanics. In this work, an innovative axially notched flattened Brazilian disc (ANFBD) sample is proposed for the mode III fracture tests of rocks using the split Hopkinson pressure bar (SHPB). Firstly, the optimal geometrical dimension of the ANFBD sample for achieving true mode III fracture of rocks is comprehensively discussed using finite element method (FEM) analysis. Then, the reliability of ANFBD-SHPB method is experimentally verified through dynamic mode III fracture experiments on the Fangshan marble (FM). Laboratory experimental results show that the mode III fracture toughness (KIIId) values of FM are approximately 2.8 times of the mode I fracture toughness (KId) values at similar dynamic loading rates. Post-mortem examinations on the fracture surfaces show that the famous facet coarsening mechanism in mode III fracture is suppressed under high loading rates. Furthermore, insightful assessments regarding the inner progressive fracturing behaviors of the ANFBD sample are given by virtue of three-dimensional discrete element method (DEM) simulation. Moment tensor (MT) analysis indicates that the shear fracture mechanism mainly dominates the whole failure process of the ANFBD sample, while the tensile fracture mechanism slightly increases during the facet coarsening process. These results are of significant importance for revealing the failure mechanism of rock under dynamic mode III loading and give some beneficial implications for natural strike-slip fault structures.

Characteristics of Pre-peak Mechanical Damage and Energy Evolution of Typical Hard-rock in Diversion Tunnel under Cyclic Loading-Unloading

An in-depth understanding of the pre-peak mechanical damage and energy-evolution characteristics of typical hard-rock in a diversion tunnel under cyclic load is of great significance to promote the safe and efficient construction of the diversion tunnel and the stability of surrounding rock. To study the pre-peak mechanical characteristics and the competition mechanism between energy storage and energy dissipation of typical hard-rock in a diversion tunnel under cyclic loading-unloading, combined with the internal drilling and blasting excavation of the actual engineering rock mass and the external vehicle cyclic load environment of the diversion tunnel, the cyclic loadingunloading tests of typical granite and tuff in diversion tunnel were carried out. Based on the analysis principle of mechanics and energy, the strain variables, modulus variables, energy variables and damage variables of granite and tuff under cyclic loading-unloading test were defined. The cyclic mechanical properties and energyevolution characteristics of granite and tuff under pre-peak load were analyzed. The competition mechanism between pre-peak energy storage and pre-peak energy dissipation of granite and tuff and the evolution law of strain damage variable and energy damage variable were revealed. The selection principle of rock sample size and the limitation of the test scheme were further discussed. The study of the damage evolution of rocks close to failure (pre-peak stage) under cyclic load is helpful to better understand the damage and failure mechanism of rocks in practical engineering problems. Keywords: Diversion tunnel, Cyclic loading-unloading, Granite/Tuff, Blasting cyclic load, Energy evolution.

True triaxial energy evolution characteristics and failure mechanism of deep rock subjected to mining-induced stress

In deep rock engineering, complex stress conditions are encountered, which leads to difficulties in engineering disaster prevention and control. To investigate the failure behaviors and mechanisms of deep rock mining, a series of tests was designed for mining-induced failure at different simulated depths using a multifunctional true triaxial geophysical (TTG) apparatus. The results showed that both the simulated depth and mining disturbance affected the deformation characteristics of the sandstone specimens. With increasing depth, the strength gradually increased. The peak strength increased fastest in the single-sided unloading failure test (SUFT) and slowest in the stress loading and unloading failure test (SLUFT). The failure mode also changed significantly. In the displacement loading failure test (DLFT), the failure mode gradually changed from tensile failure to shear failure. In the SLUFTs, the failure mode of the specimens changed from layer cracking to shear failure. In the SUFTs, the failure mode of the specimen transitioned from layer cracking to tensile shear failure and then to shear failure. Scholars have previously proposed an elastic strain energy calculation method for true triaxial stress conditions. An elastic strain energy calculation method applicable to different mining disturbance was proposed under true triaxial stress conditions, and the evolution characteristics of the work done, elastic strain energy, and dissipated energy were analyzed. Additionally, a method to quantitatively characterize the relationship between macroscopic cracks and dissipated energy was proposed, and microscopic fracture analysis was performed using scanning electron microscopy (SEM). Different depths and various types of mining-induced failure were fully considered, and the specimen deformation, failure type, energy evolution (including dissipation), and failure mechanisms were analyzed. The results can provide guidance for deep underground engineering projects.

Damage evaluation of rock blasting based on multi-fractal study

This study shows the failure mechanism of rock under blasting loads by CT scanning and utilizing fine sandstone as a test specimen. The results indicated that the 3D reconstruction technique can be employed to construct macroscopic fissures in the rock. The complexity of macroscopic fissures in the rock after blasting is quantitatively evaluated using the 3D box-counting dimension. In addition, a multi-fractal method is proposed for comprehensively evaluating macroscopic fissures and microscopic damage of rock after blasting. Compared to the numerical simulation results, the multi-fractal dimension represents the cracks and damage of rock after blasting more precisely than the simple fractal dimension. The blasting experiments of the jointed sandstone demonstrated that the 3D box dimension is suitable for evaluating the 3D macroscopic fractures of the rock after blasting and that it is a straightforward method of macroscopic evaluation. The multi-fractal dimension can evaluate the macroscopic fissures and microscopic damage of various CT scanning rock layers with greater precision.

Experimental study of the effect of crack distribution on the failure mechanism of sandstone specimens based on inclination angles and number of parallel flaws

Discontinuous joints are prevalent in engineered rock masses and play a significant role in the stability of the rock mass. This study aims to analyze the impact of the inclination angle and number of prefabricated flaws on the crack evolution and failure pattern of sandstone specimens. Uniaxial compression tests, along with acoustic emission technology and digital image technology, were employed to monitor and analyze the effects. The findings indicate that: (1) With the increase in the flaw inclination angle, the damage mode of the specimen transitions from tensile to compressive-shear failure. The localized high-strain region on the surface of the specimen predicts the propagation path for the formation of macroscopic cracks. (2) When the number of prefabricated flaws is small, the flaws mainly expand through tensile wing cracks. As the number of flaws increases, the inner flaw tip does not produce cracks. Instead, the failure of the entire specimen occurs along the direction of the outer flaw's tensile wing crack, with the inner flaw running through it. (3) The winged tensile crack is the first crack to appear in all rock samples, regardless of the flaw initiation angles. Finally, the stress intensity factor at the crack tip under uniaxial compression conditions, without considering the closure effect, was expressed based on fracture mechanics theory. The crack initiation angle was then calculated. The results of the theoretical calculation of the initiation angle were found to be consistent with the test results. These research findings can serve as theoretical references and provide insights into the failure mechanisms of cracked rocks and the development of disaster control methods in rock engineering.

Failure mechanism of hot dry rock under the coupling effect of thermal cycling and direct shear loading path

Inducing shear failure in reservoir rocks is a critical strategy for enhancing hot dry rock resource exploitation, as it promotes the development of an extensive fracture network. In this study, granite was subjected to direct shear tests under three distinct temperatures and five thermal cycling treatments. Utilizing acoustic emission (AE) and digital image correlation (DIC) techniques, the shear failure traits and the evolutionary patterns of cracks in granite under diverse thermal cycling treatments were probed. Experimental results reveal that the direct shear strength of granite initially decreases, subsequently rebounds with increasing thermal cycles, and exhibits a steady decrease with temperature increase. Effects of thermal shock provoke a surge in AE counts and energy during the initial half of the shearing process, steering the failure mode of the samples from brittle to plastic. Furthermore, the macro crack morphology changes from a singular shear crack to a pair of parallel shear cracks, becoming intricately complex at elevated temperatures (600 °C). Additionally, the initiation of the main shear crack in granite consistently manifests a mixed tensile-shear failure, with the proportion of shear action displaying a positive correlation with temperature. In contrast, the proximal secondary cracks are purely tension-initiated. Finally, a competitive mechanism between rock strengthening and weakening induced by thermal cycles treatment was proposed to explain the remarkable rebound in direct shear strength following thermal cycling treatment. The current work provides insights for the mechanism of shear failure in rocks under different thermal cycling conditions in geothermal reservoir stimulation.

Study on mechanical properties and failure mechanism of hard rock with stiff discontinuities based on 3D printing

To examine the influence of stiff discontinuities with different angles and roughness on the stability of deep hard rock engineering, RLSD is created through the integration of 3D scanning, digital modeling, and 3D printing. The specimen's composition truly reflects the mineral components of the original rock. The impact of angle and roughness on the strength, deformation, and failure characteristics of RLSD is explored by uniaxial tests. The failure process and mechanism of specimens under the influence of stiff discontinuity feature are investigated through the integration of DIC, AE, and SEM test. The study results demonstrate that achieving highly similar specimen of hard rock containing stiff discontinuities with different angles and roughness is attainable by utilizing rock-like materials based on original rock mineral components and employing a combination of 3D scanning and 3D printing techniques. The peak strength, peak strain and elastic modulus of RLSD increase with the increase of JRC, and there is a V-shaped trend of“decrease first and then increase” with the increase of angle. The failure mode of RLSD shows the change rule of tension failure - tension-shear composite failure - shear failure - tension-shear composite failure - tension failure with the increase of angle. At angles of 60° and 75°, a sudden increase in hit and energy of AE feature is observed in RLSD, resulting in brittle failure. The cumulative energy exhibits a positive correlation with JRC. Based on the test results, an empirical estimation formula is established for the uniaxial compressive strength of RLSD, considering the influence of angle and JRC. The research results can provide reference for estimating the strength of surrounding rock in deep underground engineering as well as disaster prevention and control.