In order to explore the ejection failure mechanism and energy variation law of the in-focused energy rock burst and the concentrated stress rock burst. Based on the true triaxial disturbance unloading rock test system, high-stress unloading and different second principal stress loading tests were conducted. The mechanical properties and AE characteristics of coal samples under high-stress unloading and varying secondary principal stress loading conditions have been systematically analyzed. The area of the loading and unloading curve calculates the energy of the loaded coal sample. The elastic energy and dissipation energy ratio, the pre-peak energy and post-peak energy ratio, and the dissipation energy and elastic energy ratio are used to characterize the energy accumulation, dissipation, and release behavior. The energy mutation mechanism of coal samples under different loading and unloading conditions is revealed. The results indicate that the ejection failure characteristics exhibit the characteristics of tension-shear composite failure, in which tension failure is an inevitable occurrence during the ejection failure process. Unloading is more sensitive to energy accumulation ejection failure, and the ejection failure phenomenon tends to become more evident as the unloading degree deepens. The second principal stress has a great influence on the ejection failure of stress concentration rock burst, and the intensity of ejection failure increases with the increase of the second principal stress. The energy variation law of coal samples under high stress unloading and different second principal stress loading conditions is similar. With the increase in coal sample strength, the kinetic energy, impact tendency, and ejection failure probability of coal sample ejection fragments will also increase. The more fully damaged after unloading, the more prone to ejection. The evolution characteristics of AE have three stages, such as rising period, quiet period and destruction, in which the local ejection phenomenon appears in the destruction stage. The research method is certain rationality for the analysis of the energy evolution mechanism of coal rock. The research results provide an experimental basis for the ejection failure of rock burst. To provide support for targeted classified control measures.

To explore the mechanical evolution and damage mechanisms of rock in cold regions under freeze–thaw cycles, this study selected white sandstone from mining areas in western China as the research object. Uniaxial compression tests were performed after different numbers of freeze–thaw cycles. Digital Image Correlation (DIC) was employed to analyze the deformation evolution and crack propagation characteristics, and the damage mechanisms were interpreted from the perspective of energy evolution. The results show that with an increasing number of freeze–thaw cycles, the peak stress and elastic modulus of the white sandstone decrease significantly, with the most substantial reduction occurring between the 15th and 30th cycles. The stress–strain curves exhibit a prolonged compaction stage and increased peak strain, indicating that freeze–thaw action exacerbates the accumulation of internal damage in the rock. DIC analysis reveals that freeze–thaw action causes rock deformation to concentrate at the specimen edges at an earlier stage, accelerates crack propagation, and leads to a gradual transition in failure mode from tensile failure to tensile-shear composite failure, with the degree of failure becoming more severe. Energy evolution analysis indicates that freeze–thaw cycles reduce the total input energy and the elastic strain energy at peak stress, while the proportion of dissipated energy increases, suggesting that freeze–thaw damage results in greater energy consumption through irreversible deformation. Finally, based on the Lemaitre strain equivalence hypothesis and the Weibull distribution, a damage constitutive model considering the coupled effects of freeze–thaw and mechanical loading was established by introducing correction factors, and its validity was verified.

In order to study the failure and fractal characteristics of unloaded rocks, with the help of the true triaxial unloading rock test system and the acoustic emission (AE) monitoring system, rock failure tests were conducted under varying intermediate principal stress and the mechanical response features of the rocks were analyzed. An investigation was conducted into the rocks’ AE patterns and multifractal features. The results showed that the rocks’ AE macroscopic and microscopic main failure modes differed slightly under unloading. As the intermediate principal stress σ2 increased, the fractal dimension of the cracks in the rocks first increased and then decreased. The distribution of rock failure was initially concentrated, then dispersed, and concentrated again at the end. As the σ2 increased, the number of failure events within a specified area in the rock samples under unloading, as represented by the ring-down count, first increased and then decreased. Meanwhile, the fractal dimension Δα first decreased and then increased. These results characterized the process whereby the failure distribution pattern of the rocks changed from being concentrated to dispersed and back to concentrated again.

Accurately predicting rock tensile strength under varying strain rates is crucial for tunnel construction, as rock often fails in tension. This study examines the effect of rock mesostructure on tensile strength using a breakable grain-based model (GBM) implemented within the UDEC software. The Brazilian disk model was established to simulate the quasi-static and dynamic tensile behaviors of rocks under varying mineral average grain sizes, grain size distributions, and grain roundness, respectively. Simulation outcomes indicate that mesostructure significantly influences rock tensile strength. The breakable GBM effectively captures the tensile failure process under high strain rates, revealing the role of grain structure heterogeneity in strain rate effects. Additionally, the study evaluates the applicability of different dynamic increase factor (DIF) models, confirming the effectiveness of the normalized DIF model for predicting the dynamic tensile strength of granite. These findings underscore the importance of considering rock mesostructure for accurate prediction and enhancement of rock performance under dynamic loading conditions.

To investigate the failure behavior and cracking mechanisms in surrounding rock, a true triaxial experimental system and digital imaging were employed to perform compression tests on sandstone specimens containing preexisting flaws. Experimental results revealed the propagation characteristics of microfractures under stress concentration conditions and their correlation with failure patterns. Furthermore, a fracture propagation model was implemented to evaluate the susceptibility of surrounding rock to failure. Macroscopic analysis identified four distinct failure phases: quiescent, particle ejection, stable damage, and structural collapse. The load-bearing capacity demonstrated positive correlation with in situ stress magnitude, while deformation accommodation capacity followed a nonmonotonic trajectory characterized by initial enhancement followed by deterioration. Furthermore, the analysis of influencing factors on surrounding rock failure identified the order of sensitivity as in situ stress > crack angle > crack size > friction coefficient. Furthermore, the reason for V-shaped failure crater of surrounding rock was clarified through intermediate parameter of critical compressive strength. This research provides valuable insights that can be referenced for designing strategies to control roadway stability.

To investigate the influence of fissure inclination angle and position on the creep mechanical properties and failure characteristics of rock, stepwise loading uniaxial creep experiments were conducted on fissured rock-like materials. A numerical model of fissured rock was established using the PFC program. The constitutive equations and creep equations for the numerical model were derived and solved. Precise simulation of the entire creep process was achieved through the calibration of mesoscopic parameters. The creep deformation characteristics and crack propagation patterns of fissured rock with different inclination angles and positions were studied. The results indicate that: (1) The fissure inclination angle significantly affects specimen strength and deformation characteristics. A smaller inclination angle leads to a greater reduction in specimen strength. Under identical stress levels, specimens with 30° fissures exhibited the largest axial strain, while those with 0° fissures showed the smallest. (2) Analysis of displacement field evolution during creep revealed that the fissure inclination angle alters the distribution of shear and normal displacements around the fissure, thereby influencing crack propagation paths and failure modes. (3) Fissures closer to the specimen top detrimentally affect overall stability. For low-angle fissures (0°, 30°), positioning 20 mm above the specimen centroid resulted in the highest strain and the lowest creep failure stress, indicating the most unfavorable location. The macroscopic failure mode is influenced by fissure position. As the fissure position elevates, the macroscopic creep failure modes of specimens with different inclination angles exhibit specific transformation patterns.

To investigate the failure mechanism and establish stability control methods for surrounding rock in high geo-stress roadways, this study incorporated the brittle failure characteristics of the surrounding rock mass into a unified strength criterion, developing an elastic-plastic theoretical model to represent rock damage and fracture. Using this model, analytical expressions for the damage rupture radius and stress field distribution are derived, leading to the proposal of a grading control method. The analysis of calculation examples reveals that an increase in stress, damage degree, and the brittleness coefficient of the rock mass results in the expansion of both the plastic damage and damage residual zones. Conversely, an increase in the intermediate principal stress coefficient and support resistance reduces the extent of these zones. The proposed grading control strategy includes three levels: Level I focus on preventing cracks through initial support, Level II involves reinforcing anchor injections to reduce cracks, and Level III applies local borehole pressure relief. Implementing this strategy can significantly reduce stress concentration and deformation in the surrounding rock, providing valuable insights for roadway support control.

To investigate the effects of wet-dry cycling on the dynamic tensile strength and failure characteristics of limestone, this study conducted dynamic impact loading experiments on limestone specimens subjected to varying numbers of wet-dry cycles using a Split Hopkinson Pressure Bar (SHPB) system. By integrating digital image correlation (DIC) and fractal analysis, the stress-strain evolution, crack propagation patterns, and energy dissipation mechanisms under different loading rates and wet-dry conditions were systematically analyzed. Results indicate that wet-dry cycling significantly degrades limestone’s mechanical properties, reducing tensile strength and promoting complex crack propagation. Energy distribution and dissipation were also substantially influenced. While dynamic tensile strength improved with increasing loading rates, the weakening effect of wet-dry cycles became more pronounced. Additionally, interactions between main and secondary cracks grew more intricate with prolonged cycling. The fractal dimension of fragmentation increased linearly with cycle number, though sensitivity gradually declined. These findings advance the theoretical understanding of limestone failure mechanisms under coupled wet-dry cycling and dynamic loading. They also offer practical insights for mining engineering and blast design applications.

The final macroscopic fracture of coal rocks is closely related to their internal microscopic structure and micro-defects. The continuous change of the microscopic structure of coal rocks is the main reason for the change of the macroscopic mechanical properties. This change in macroscopic mechanical properties is caused by the unloading damage, which is closely related to the ejection phenomenon of coal rocks. The porosities of the coal rocks before and after tests are measured by the nuclear magnetic resonance (NMR) technique, and the T2 spectrum distribution, porosity, and nuclear magnetic resonance imaging of different coal rocks under the unloading action are obtained. The evolution characteristics of pore structure are analyzed, and the unloading damage mechanisms of different coal rocks are revealed. The damage formula is established based on NMR results, and the damage variables are derived and characterized quantitatively. The results show that the larger the initial damage, the larger the porosity, and the greater the damage under the same unloading confining pressure ratio. This indicates that initial damage plays a leading role in the damage of coal and rock, and ejection is more likely to occur under unloading conditions. With the decrease of confining pressure, the porosity of YTX increases obviously, the connectivity between pores increases, and obvious cracks appear. The research results provide an experimental basis for studying the damage evolution process and micromechanics of coal rock, establishing a bridge between the microdamage mechanism and macro fracture analysis of coal rock.

To explore the interaction between holes and fractures in defective white sandstone, uniaxial compression tests were conducted on samples with varying horizontal distances between holes and fractures. The technique known as Digital Image Correlation (DIC) was employed to analyze the deformation patterns, while CT scanning technology was implemented to elucidate the interior crack propagation features. Discrete Element Method (DEM) simulations were performed to investigate the micro-scale fracture evolution. The findings demonstrate that load-bearing capacity and deformation resistance decreased as the horizontal hole-fracture distance increased. The failure mode transitioned from a mixed tensile-shear failure to a more rapid tensile failure. Tensile wing fractures caused by tensile failure reinforced the merging of rock bridges. Furthermore, the trajectories of fracture propagated from the outside to the inside of the rocks progressively simplify, resulting in accelerated instability and collapse. DEM simulations indicate that the augmentation of horizontal distance between holes and fractures influenced the displacement field and the orientation of micro-fractures inside the samples. The formation of micro-fractures progressively adhered to a “clusteringexpansion-coalescence” sequence along the paths of the hole-fracture structures. The maximum strength of the samples declined in a three-phase pattern: gradual decline, steep decline, and gradual decline. These findings provide valuable insights for engineering applications, such as tunnel excavation and mining operations.

To investigate the failure behavior of the roadway surrounding rock under varying in-situ stress conditions, a series of small-scale model experiments were carried out using a true triaxial rock testing system, an acoustic emission (AE) monitoring system, and a miniature camera monitoring system. The experiments utilized prefabricated cubic sandstone specimens with through-holes to simulate the stress environment of the circular roadway, analyzing the AE characteristics of the failure process of the surrounding rock. The experimental findings indicated that the failure of surrounding rock can be categorized into four stages: the quiet stage, particle ejection stage, stability failure stage, and collapse stage. As the in-situ stress increased, the sustained stress during the quiet stage was negatively relative to the sustained stress during the particle ejection stage and positively related to the sustained stress during the stability failure stage. Moreover, the dominant AE signals during the particle ejection stage shifted from mid-frequency to high-frequency. In the stability failure stage, the ratio of low- to high-frequency (LF to HF) signals increased, the predominant failure mode transitioned from shear failure to tensile failure, and the fissure growth pattern changed from intermittent bursts to progressive development. Data from the RA (Rise Time/Amplitude) and AF (Average Frequency) analysis indicated that the predominant failure mode of deep roadway surrounding rock was tensile fractures, which intensified with increasing in-situ stress.

With the goal of examining the micromechanics damage characteristics of freeze-thaw red sandstone under the influence of cyclic loads, a model of freeze-thaw cyclic rock particles is developed based on Discrete Element Method numerical simulation in order to investigate and study the micromechanics response mechanism of rocks under the coupling effect of freeze-thaw and cyclic loads. The findings demonstrate that lower rock elastic modulus and higher irreversible strain are driven by longer loading/unloading durations and more frequent freeze-thaw cycles. Its bearing capacity and resistance to deformation are diminished by the damage brought on by freeze-thaw; Rock anisotropy and the spatial organisation of microcracks are significantly altered by different loading techniques; In freeze-thaw rocks, the frequency and intensity of acoustic emission breaking follow the law of normal distribution. Under cyclic stress, samples exposed to several freeze-thaw cycles exhibit an escalation in large-scale fractures, accompanied by a concentrated spatial distribution of acoustic emission events. Three phases may be distinguished in the energy evolution of red sandstone: the initial, accumulation, and release phases. The energy storage capacity is compromised by freeze-thaw degradation, resulting in an elevated conversion rate of dissipative energy and rendering the energy conversion mechanism more unstable. The previously described study results possess considerable relevance for rock engineering construction and catastrophe mitigation in cold climates.

In response to the challenges posed by long-term cyclic loading and unloading in underground rock engineering, this study systematically investigates the macro- and meso-mechanical response mechanisms of fractured rock masses under cyclic loading conditions. We performed graded cyclic loading–unloading tests on parallel double-fractured sandstone samples with varying spatial distribution configurations. These tests were integrated with digital image correlation (DIC) technology, fractal dimension analysis, and discrete element method (DEM) numerical simulations to analyze the mechanical properties, deformation characteristics, crack propagation features, and meso-fracture mechanisms of the fractured rock masses. The findings indicate that the diverse spatial distribution characteristics of the double fractures exert a significant influence on the loading–unloading processes, surface deformation fields, and fracture states of the rock. Cyclic loading leads to an increase in the fractal dimension of the fractured samples, resulting in more intricate and chaotic crack propagation patterns. Furthermore, DEM simulations reveal the impact of fracture spatial configurations on the force chain distribution within the rock bridges. The equivalent stress nephogram effectively represents the stress field distribution. This offers valuable insights for predicting meso-fracture trends in rocks. This paper comprehensively integrates both experimental and numerical simulation methodologies to deliver a thorough analysis of the complex mechanical behavior of fractured rock masses under cyclic loading conditions, with direct relevance to engineering applications such as mine excavation and slope stabilization.

To investigate the mechanical properties and energy evolution laws of rocks under true triaxial unloading conditions, a study was conducted using a true triaxial rock testing system on three different types of rocks: coal, sandy mudstone, and siltstone. The study examined the mechanical behavior, failure patterns, and fractal dimensions of these rocks under true triaxial unloading conditions. The tests revealed significant variations in stress–strain curves and failure patterns among the different rock types. Observation indicated that rocks with lower peak strength exhibited higher fractal dimensions and increased fragmentation upon failure. Subsequently, based on the experimental data of siltstone, the impact of the unloading rate and particle size distribution on the energy evolution under true triaxial single-sided unloading paths was further investigated using the three-dimensional particle flow software PFC3D 6.0, revealing the micro-mechanisms of rock energy evolution. The study revealed that when the initial stress unloading level was low, the total energy and strain energy at the peak strength exhibited a strong linear relationship with the unloading rate. Before the stress peak, the dissipative energy was mainly composed of frictional energy. After the stress peak, the dissipative energy consisted of frictional energy, damping energy, and kinetic energy. The heterogeneity of rock significantly affected the distribution of dissipative energy, with an increase in rock heterogeneity leading to a decrease in frictional energy and an increase in kinetic energy.

The mechanical behavior of rock masses is significantly influenced by the presence of internal holes. This study investigates these effects through uniaxial compression tests and two-dimensional Particle Flow Code (PFC2D) numerical simulations on sandstone samples containing triangular holes with varying apex angles. The results reveal a distinct “W” pattern in both peak strength and elastic modulus as the apex angle increases. For holes with angles less than 60°, cracks preferentially initiated at the apex and propagated along the AB side. In contrast, angles of 60° or greater resulted in crack initiation at the base corners, with damage concentrating along the BC side. This behavior underscores the combined influence of hole area and angular geometry on the strength of the specimens. Acoustic emission monitoring during testing enabled the definition of a damage variable, which was subsequently used to develop a constitutive model based on the Duncan model. The proposed model effectively captures the distinct stages in the stress–strain curves, demonstrating both accuracy and practical relevance.

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The mesostructure of brittle rocks, such as granite, plays a vital role in determining their mechanical properties and failure mode. Understanding the influence of rock mesostructure on mechanical behavior requires a realistic representation of grain size distribution, grain shape, and average grain size. In this study, we developed a breakable polygonal discrete element model that incorporates mineralogical composition, grain size distributions, and grain shape to simulate the rock mesostructure. Numerical specimens with varying mesostructures were created to represent different grain size, shape, and distribution characteristics. Quasi-static uniaxial compressive loading tests were conducted on these specimens to analyze their peak strength and macroscopic failure modes. The results revealed a strong linear relationship between the quasi-static compressive strength of the rock and mesostructure parameters, including average grain size, grain size coefficient, and grain roundness. Additionally, the simulation results demonstrated that the rock mesostructure significantly influenced the quasi-static compression failure mode. The proposed breakable polygonal discrete element model has the potential to predict the macroscopic behavior of brittle rocks accurately. It provides a reliable method for studying the effect of mesostructure on the quasi-static compressive mechanical behavior of rocks.

Deep-hole bench blasting is the primary method for aggregate extraction in mines. However, factors such as complex geological conditions and suboptimal blasting parameters often result in uneven rock fragmentation and high fines content. This not only increases the cost and energy consumption of subsequent aggregate processing but also has adverse environmental implications. In this study, based on the Changjiu Shenshan limestone aggregate mining project in China, large-scale blasting experiments were conducted to investigate the influence of rock properties and blasting parameters on the size distribution of post-blast fragments and fines content. The results of the blasting experiments indicate that by controlling the size of the crushing zone and adjusting explosive performance, it is possible to significantly reduce fines content while improving mining efficiency. Recommended values for drilling and blasting parameters have been proposed based on geological conditions to more effectively control the generation of fines. The results highlight the importance of optimizing blasting parameters and charge structure for large-scale mining operations to achieve uniform rock fragmentation and low fines content. By adopting explosive performance adjustment methods based on reasonable control of the crushing zone, improving explosive performance can improve the economic benefits of mining operations, reduce energy consumption, and contribute to environmental protection.

To study the fatigue failure of an intermittent jointed rock mass under repeated stress waves, numerical models of jointed rock masses with different joint angles were created using Autodyne software, and crack propagation behavior was simulated using the Drucker–Prager strength model and cumulative damage failure criteria. In this numerical simulation, the influence of stress wave amplitude and the mode of disturbance on fatigue failure of the rock mass were analyzed. The simulation results showed a significant difference between the failure process of jointed rock masses subjected to repeated stress waves and those exposed to a single stress wave, including crack initiation locations, propagation paths, and rock mass failure patterns. With increasing angles of inclination, the fatigue life of the rock mass first decreased and then increased under repeated stress waves. As the joint inclination angle, β , increased from 20° to 50°, it had a significant influence on the fatigue life of the rock mass, which decreased rapidly with increases in β. The variation in the disturbance form (the change in amplitude of the stress waves from small to large, or from large to small) did not affect the final macro failure pattern of the rock mass; but the extent of damage to the rock mass was affected.

Nowadays, with many available numerical methods developed in rock mechanics, researchers have always focused on the parameter calibration of the numerical model but ignored the predictive capability of these methods. A comparative study of nine commonly used numerical methods was performed for predicting rock failure through international cooperation organized by the Discontinuous Deformation Analysis (DDA) commission of the International Society for Rock Mechanics (ISRM). Two steps of numerical modelling were conducted including a calibration procedure from given experimental results and a numerical prediction for benchmark tests with these calibrated parameters for three types of rocks. Through the comparison between different numerical and experimental results, the inherent weaknesses and strengths of different numerical methods in terms of predicting rock failure were identified and analysed. The influence of human intervention in terms of parameter selection is even more significant than the choice of different numerical methods. Some potential factors (i.e., different boundary conditions, heterogeneity of rock material, strength parameters, particle packing, and failure criteria) that may occur in numerical and physical tests were further discussed. Through the comparison of different failure criteria, we found the selection of rock failure criterion might be the major factor that affected the predictive capability of numerical methods, and the nonlinear failure model (the Hoek–Brown criterion) showed the superiority in the prediction of rock fracturing subjected to complex stress conditions. This comparative work also enlightens the significance of a high-quality calibration process and the future advancement of rock failure criteria.