Mechanical Properties Of Rock Mass Research Articles

Conversion, prediction, and application of strength and stiffness parameters for grouted reconstructed rock mass

Ultrasonic detection has emerged as a rapid method for acquiring rock mass sound velocity and converting it into an elastic modulus parameter, a pivotal technique for investigating the in-situ mechanical properties of rock masses. Despite its significance, accurately deducing rock mass strength from elastic modulus remains a formidable challenge and a pressing issue in the realm of protorock parameter research. This study introduces an innovative artificial intelligence-driven methodology for transforming elastic modulus and strength parameters specific to coal measures through rigorous data analysis and experimental validation. By integrating two illustrative engineering cases, we explore the complexities of water inrush and floor heave issues encountered in tunnels traversing fault zones. The novel strength parameter calculation approach is benchmarked against previous studies, highlighting its superior advantages in terms of effectiveness and applicability. In essence, this research offers a comprehensive framework and practical workflow for translating in-situ acoustic parameter-derived elastic modulus into rock mass strength, serving as a valuable resource for future endeavors in mine water control research.

In-situ Rotary Cutting System for Estimating the Mechanical Parameters of Rock Masses

A rock mass in-situ rotary cutting test system (RMIRCS) was developed to estimate the mechanical properties (i.e. compressive strength and elastic modulus) of rock masses. The pressure-on-bit and torque-on-bit of the RMIRCS were investigated in detail over a wide range of revolution speed and penetration rate. A simple experimental model is proposed to describe the qualitative relationships between rotary cutting test data and mechanical parameters. The existence of a linear constraint between pressure-on-bit and torque-on-bit and the depth of rotary cutting exhibits good agreement with the proposed model. The mechanical properties obtained from the quasi-static compression tests were in agreement with those of the RMIRCS at lower revolutions rate of 300 rpm and 350 rpm, which suggests that the developed RMIRCS is valid. Furthermore, the experimental test results on rock mass demonstrated that the mechanical properties of rock masses are revolutions speed-dependent and drilling rate-dependent.

Experimental and analytical study on non-tip initiation behavior of three-dimensional non-planar cracks in rock-like materials

The presence of fractures, joints, bedding planes, and faults within rock masses results in their inherent heterogeneity and discontinuity. These structural defects alter the mechanical properties of rock masses, reducing their structural strength and stiffness, and contributing to anisotropy. In addition to planar cracks, non-planar cracks are frequently found within rock masses due to geological evolution and local stress variations. While the mechanisms of planar crack propagation and fracture in both two-dimensional and three-dimensional spaces have been extensively studied and understood, research on non-planar cracks has largely been confined to two-dimensional aspects. This study addresses the limitations by successfully creating brittle solid specimens with three-dimensional non-planar internal cracks. Uniaxial compression tests and numerical simulations were conducted to investigate the propagations and fracture behaviors of various shapes of three-dimensional non-planar internal cracks. The experiments identified two primary macroscopic failure modes: symmetric non-planar internal cracks exhibiting non-tip initiation failure, and asymmetric non-planar internal cracks displaying tip initiation on the upper side and non-tip initiation on the lower side. The failure strengths of non-planar internal cracks were significantly higher than those of planar cracks, and the size of the cracks had minimal effect on their failure strengths. Notably, from initiation to failure, symmetric non-planar internal cracks did not generate any wing cracks, whereas asymmetric non-planar internal cracks were accompanied by petal-shaped cracks, wing cracks, and lance-shaped cracks. Under uniaxial compression, non-planar internal cracks propagated at extremely high speeds, resulting in rough and uneven fracture surfaces. In addition to Type III lance-shaped cracks, dynamic fracture characteristic areas and Wallner lines were also observed on the fracture surfaces. This study provides valuable insights into the fracture behavior of three-dimensional non-planar cracks and a reference basis for understanding their propagation and failure mechanisms.

Failure mechanisms and reinforcement support of soft rock roadway in deep extra-thick coal seam: A case study

The soft rock roadway in deep extra-thick coal seam is prone to large deformation disaster. In order to solve this problem effectively, taking the W3101 coalface of Xiao’kang coal mine as the engineering background, the failure mechanisms and the corresponding control technology were investigated by the methods of laboratory test, numerical simulation and field measurement. First, a series of tests were carried out on the basic mechanical properties of rock mass, in-situ stress and loose zone, and it was found that the failure mechanisms of soft rock roadway in deep extra-thick coal seam are poor lithology of surrounding rock, high in-situ stress, large loose circle and unreasonable original support. Then, based on the supporting mechanisms of grouting cable and concrete-filled steel tube (CFST) of bottom angle, a new collaborative reinforcement support (CRS) technology combining the two was proposed. Next, the numerical simulation shows that the CRS technology has good applicability in controlling large deformation of soft rock roadway in deep extra-thick coal seam. Finally, to exhibit the engineering application effect of the proposed CRS scheme, it was also applied in Xiao’kang coal mine. Comparing to the controlling effect of original support scheme, it can be seen that the average deformation of soft rock roadway reduces by 73.2 % under the proposed CRS scheme, and the steel arch frame of bottom angle is slightly deformed. Meanwhile, it is found that the grouts diffusion radius is nearly 1.21 m, and the deepest diffusion depth is 4.25 m, which also indicates again that the feasibility of the proposed CRS scheme in controlling large deformation of soft rock roadway in deep extra-thick coal seam.

Study on the Influence of Temperature and Water Content on the Static Mechanical Properties of Sandstone.

The area of permafrost worldwide accounts for approximately 20% to 25% of land area. In cold-climate regions of China, which are garnering international attention, the study of low-temperature and moisture effects on rock mass mechanical properties is of significant importance. China has a wide area of cold regions. This research can provide a foundation for China's exploration activities in such extreme environments. This paper examines the mechanical behavior of rock specimens subjected to various low temperatures and water contents through uniaxial compression tests. The analysis encompasses failure modes, stress-strain relationships, uniaxial compressive strength (UCS), and elastic modulus (EM) of these specimens. Findings reveal that at lower temperatures, the rock specimens' fracture patterns transition from compressive shear failure to cleavage failure, reflecting a shift from a plastic-elastic-plastic to a plastic-elastic response. Specifically, saturated rocks exhibit a 40.8% decrease in UCS and an 11.4% reduction in EM compared to their dry counterparts. Additionally, in cold conditions, an increased water content in rocks primarily leads to vertical cracking. Under such conditions, saturated rocks show a 52.3% decline in UCS and a 15.2% reduction in EM, relative to their dry state.

Drilling Process Monitoring for Predicting Mechanical Properties of Jointed Rock Mass: A Review

Reliably assessing the quality and mechanical properties of rock masses is crucial in underground engineering. However, existing methods have significant limitations in terms of applicability and accuracy. Therefore, a field measurement method that meets the real-time monitoring and safety requirements for the quality of engineering rock masses is needed. Firstly, the research findings of domestic and international scholars on the application of drilling process monitoring technology are comprehensively analyzed. Rotary cutting penetration tests are conducted on tuff rock masses containing fractures and joints. Various rock mass classification and evaluation standards are integrated with rotary penetration tests. Rotary cutting penetration tests are used to determine the residual strength of rock, based on this review. The rationality of the calculated mi parameter values is validated. The peak strength, residual strength, and errors of the rock are obtained based on the penetration method. The rock quality index rock quality designation from drilling (RQDd) is redefined, based on the drilling process monitoring apparatus (DPMA). Rock mass classification is conducted, based on the correlation between the standard deviation of rotary drilling energy and the rock quality designation (RQD). Additionally, a new relational formula is introduced to determine the RQD from variations in drilling energy, based on discontinuity frequency. This field measurement method undoubtedly provides a crucial scientific basis for rock design and construction, ensuring long-term safety in engineering applications.

Experimental and numerical investigation of the fracture behavior in granite specimens with two co-planar side flaws under biaxial loading

It is well known that the structural plane plays a decisive role in the mechanical properties of rock mass. To better understand the cracking mechanism and stress characteristics of co-planar intermittent double-flawed granite specimens with various dip angles (Abbreviated as flawed specimens), two co-planar flaws were prefabricated on both sides of the granite, and biaxial compression tests were conducted. The failure characteristics and local microstrain were recorded by the camera and strain acquisition instrument. The evolution law of mechanical parameters of flawed specimens was analyzed. Simultaneously, a two-dimensional particle flow code (PFC2D) was used to establish a biaxial compression model of flawed specimens. The crack initiation and propagation of the specimens were explained by the crack hot spot, the evolution law of crack, and the evolution law of the number of microcracks. It is found that (a) as flaw dip angle (α) increases, peak strength and elastic modulus initially decrease and then increase, with reductions ranging from 17.6% to 46.1% and 15.6% to 48.2%, respectively. (b) Increasing lateral stress (σ2) triggers a shift in failure mode from a tensile-shear mixed failure to a shear failure. The cohesion (c) and friction angle (φ) of flawed specimens were notably smaller compared to those of intact specimens, with reductions correlating with the α. (c) Flawed specimens exhibit pronounced contact force concentration and stress concentration at the flaw tip. The analysis of the microstrain confirms stress concentration at the flaw tip, leading to failure. However, various σ2 induces the differences in the magnitude and extent of tip stress.

Study on meso-deformation and failure mechanism of rock mass with micro-cracks under freeze-thaw loading

The long-term freeze-thaw effect leads to the development of rock fractures and strength degradation in cold region engineering construction, which poses a serious challenge to the stability of the project. In this paper, the microscopic model of sandstone freeze-thaw cycles was established using a particle flow code (PFC2D). Through numerical simulation, the variation law of mechanical properties of rock mass with micro-cracks is systematically studied from the aspects of displacement, crack development, strain and strength. The results show that: (i) The freeze-thaw loading displacement is concentrated on both sides of the initial micro-cracks, and the crack development is not controlled by it. When the number of freeze-thaw cycles is greater than 17, the displacement and crack development are significant. The crack increases with the increase of the crack distance ratio. (ii) When the number of freeze-thaw cycles is less than 15, the compressive crack develops at the end of the initial micro-crack, and the development is controlled by it. When the number of freeze-thaw cycles is greater than 21, the crack increases sharply, and the development is no longer controlled by the initial micro-cracks. When the number of freeze-thaw cycles is less than 15, the damage strain shows minimal variation but decreases sharply with the increase of freeze-thaw cycles. (iii) Under each crack distance ratio, the strength changes in three stages: when the number of freeze-thaw cycles is less than 15, the strength changes little, and the strength decreases sharply with the increase of freeze-thaw cycles. With the increase of the crack distance ratio, it increases first and then decreases. And it is more significant when the number of freeze-thaw cycles is greater than 17. The research results can provide theoretical support for the influence and evaluation of rock freeze-thaw action in cold regions.

Failure mechanism and treatment of mine landslide with gently-inclined weak interlayer: a case study of Laoyingzui landslide in Emei, Sichuan, China

The landslide of mine is of great harm and wide influence, which can easily cause huge economic losses and endanger the life safety of workers. Therefore, landslide failure mechanism and more efficient landslide treatment methods have been the focus of landslide research. Laoyinzui landslide with a volume of 250,000 m3 occurred along the gently inclined weak interlayer at 6:00 (UTC + 8) on 5 January 2019 in Huangshan Limestone Mine, Emei City, Sichuan Province, China. The deformation history and failure mechanism of the landslide were analyzed based on the field investigation and geological conditions of landslide area. The treatment method of using excavators to remove all sliding body within the arm length by excavating the small-bench in the bedrock was proposed. The slope stability after treatment was analyzed based on the monitoring data. The results showed that the landslide was triggered by rainfall and earthquake after long-term creep deformation under the action of various factors. Weak interlayer was the potential sliding surface of landslide. The tensile cracks at the back edge of the landslide and the joint fissures and karst caves of the upper limestone provided convenient conditions for rainwater infiltration. Mining activities, including excavation and blasting, resulted in deterioration of mechanical properties of rock mass. Rainfall was the main trigger for the landslide. Water accumulated in weak interlayer, leading to increase of pore water pressure and decrease of anti-sliding force. Earthquake was the trigger for the landslide, which resulted in the reduction of rock mass structural strength. The Laoyingzui landslide consisted of two stages. First, a traction landslide of + 825 m–915 m occurred, and then a push landslide of + 725 m–+ 825 m occurred under the compression of the upper rock mass. The slope displacement was small and the deformation tended to be stable. The treatment method was safe and efficient. This paper can provide reference for the failure mechanism research and treatment of similar landslides.

Investigation of Sandstone-like Material for Damaged Rock Mass Based on Orthogonal Experimental Method

The investigation of the mechanical properties of rock mass can be effectively carried out through rock-like material experiments. In this study, polystyrene foam particles were utilized as a novel material for simulating initial damage within rocks. Our research involved the development of sandstone-like materials with comparable mechanical properties to actual sandstone. These materials were then subjected to orthogonal mechanical tests, allowing us to identify the key factors that have a substantial impact on the mechanical parameters of sandstone-like rocks. The influencing factors considered in the orthogonal mechanical tests were the proportion of aggregate and binder, the proportion of polystyrene foam in the entire model, the proportion of binder and regulator, and the size of polystyrene foam. Five levels were set for each factor, and mechanical parameters such as compressive strength, tensile strength, elastic modulus, axial strain, and Poisson’s ratio were tested for each group of samples. The changes in mechanical parameters with the levels of the above four factors were studied. The study found that modifying the proportion of aggregate to binder can alter the elastic modulus, tensile strength, and compressive strength values of sandstone-like material. The size of polystyrene foam can be modified to alter the axial strain values of sandstone-like materials. Additionally, adjusting the ratio of binder and regulator can modify the value of Poisson’s ratio. The comparison of mechanical parameters between sandstone-like samples and sandstone reveals that sandstone-like materials can better simulate the deformation and failure mechanisms of sandstone. The error in the main mechanical parameters, such as modulus of elasticity, strength, and Poisson’s ratio, is less than 7%, indicating a greater resemblance between sandstone-like materials and sandstone. Therefore, sandstone-like materials can be used to investigate the deformation law, damage evolution law, and failure mechanism of sandstone. This can help alleviate the difficulty of obtaining specimens of deep damaged rock and the high cost of testing.

Research on Mechanical Properties of Rock Mass with Tiny Cracks under FTCs Conditions

After the repeated freezing and dissolution of fractured rock masses in cold regions, the liquid present in the pores undergoes a water–ice phase transition, resulting in frost heave forces and damage to the internal structure of the rock mass. This causes the rock masses to continuously develop new cracks, which further expand and connect, leading to rock mass failure and ultimately reducing the overall stability of the rock mass in engineering projects. In this study, uniaxial compression tests, direct shear tests, and Brazilian splitting tests were conducted on rock after freeze–thaw cycles (FTCs), and the changes in the physical and mechanical properties of the rock under freeze–thaw conditions were obtained (this study used raw rock from an engineering project and processed it into symmetrical jointed rock samples). The roughness of the shear fracture surfaces was analyzed through 3D cross-sectional scanning experiments. Using statistical damage theory, the mechanism of freeze–thaw damage was analyzed, and a constitutive model for freeze–thaw rock damage was established. The research results can provide a theoretical basis and support for engineering safety and stability in cold regions.

A precise modeling method of three‐dimensional discrete fracture network based on rectangular joint model

AbstractAs the weak structure and main seepage channel of rock mass, the discrete fracture network (DFN) has a significant influence on the physical and mechanical properties of rock mass. In this paper, based on the rectangular joint model, two algorithms are proposed to realize the precise modeling of the DFN in any polyhedron. First, the equivalence of DFN modeling with the rectangular joint model and the elliptical joint model is theoretically deduced. On this basis, the chain splicing algorithm suitable for the rectangular joint model is proposed, which can generate the DFN model according to the actual distribution of joint spacing, trace, and bridge length. Aiming at the concave boundary in the model domain, the segmentation‐stitching operation is put forward, and the continuity of the joint when passing through the interface is ensured. Finally, the effectiveness of the above algorithm is verified by several simple cases, and the relationship between the size of the geometrical representative elementary volume (REV) and discontinuity parameters is discussed. The results show that when the mean values of the joint distribution parameters are the same, even if the distribution rules are different, the number of joints generated in the same spatial region is approximately equal. The size of the geometrical REV is independent of the spacing and bridge length and is approximately three to five times the mean of the trace. The relevant algorithms and conclusions in this paper can be used as the basis for subsequent rock mass stability analysis and seepage calculation.

The effect of joint inclination angle on mechanical properties of rock mass studied by model test and DEM simulation

The joint inclination angle is a crucial factor influencing the mechanical behavior of rock masses and greatly affects the stability of rock mass engineering. The article utilizes cement mortar to fabricate jointed rock models with mechanical properties that closely resemble those of real rock formations. The compressive plate speed of the loading test machine is 0.005 mm/s, and the axial static loading rate ranges from 0.5 to 1.0 MPa/s. To investigate the influence of joint inclination angles on the macroscopic mechanical properties of the rock, the study initially employs indoor full-field observation and the non-contact technology known as Digital Image Correlation (DIC). Experiments are conducted on rock specimens with varying joint inclination angles of 30°, 45°, 60°and 90°. Following this, numerical simulations employing the Discrete Element Method (DEM) are conducted to analyze the microfracture process. The model test and numerical simulation results demonstrate good agreement, particularly regarding the failure modes. It is found that the most common failure mode for jointed rock is a composite form of shear and tension. As the joint inclination angle increases, tensile failure becomes more prominent. The Young’s modulus EJR/ER and peak strength σJR/σR ratios between jointed and jointless rock vary with the joint inclination angle, exhibiting a "V" shaped curve. A joint inclination angle of 45° results in minimum strength and modulus in the macro mechanical properties. The joint inclination angle has a negligible effect on the rock mass’s residual strength, maintaining an approximately constant ratio of 0.14 between residual and peak strength σr/σp .

Macro- and micromechanical properties of flawed sandstone and their degradation mechanisms under hydrodynamic scouring

To reveal the degradation mechanisms of the mechanical properties of a rock mass in a reservoir bank slope under hydrodynamic scouring, a hydrodynamic scour test device was developed in this study. Sandstone specimens containing prefabricated flaws were used as the research objects. Three conditions, namely, natural conditions, hydrostatic immersion, and hydrodynamic scouring, were considered. By considering the results of laboratory testing, digital image correlation (DIC), scanning electron microscopy (SEM), and thermodynamic analysis and fractal theory, the effects of different flow states on the mechanical properties of the flawed rock mass were systematically investigated in terms of the macromechanical parameters, strain field, strain energy, and microstructure. A crack initiation stress identification method based on the differentiation rate of the effective variance of strain fields was proposed. The energy conversion in the rock loading process was quantitatively characterized using three strain energy characteristic indicators. The internal microstructure of the rock was quantitatively characterized using a combination of SEM image characteristics and the fractal dimension. It was found that the uniaxial compressive strength, elastic modulus, crack initiation stress, energy storage limit, elastic strain energy conversion rate, and dissipated strain energy conversion rate of the hydrodynamically scoured specimen were the smallest, while the fractal dimension was the largest. There was a strong correlation among the mechanical parameters, energy characteristic indicators, and fractal dimensions of differently treated sandstone specimens because the macromechanical response and energy conversion characteristics of a rock mass are closely correlated with changes in its internal structure.

Mechanical characterization of intermittent weak interlayer based on DIC and acoustic emission technique

Current research on intermittent structural surfaces tends to concentrate on intermittent joints, often neglecting the abundance of intermittent weak interlayers present in rock structures. To analyze the effect of intermittent weak interlayer on the mechanical properties of rock mass, specimens with varied interlayer thickness and dip angles were prepared and subjected to uniaxial compression tests using an acoustic emission system and Digital Image Correlation (DIC) technique. The results revealed an inverse relationship between the interlayer thickness (t) and dip angle (θ), and the uniaxial compressive strength. Through a nonlinear fitting method, an empirical strength equation for these interlayers was established. Acoustic emission (AE) counts and cumulative acoustic emission counts increased with loading, and the RA-AF values indicated that the specimens were dominated by shear damage, and the larger the thickness and dip angle of the interlayer, the higher the proportion of shear damage. In terms of failure mode, the greater the thickness of the interlayer, the lower the level of development of cracks other than the main crack, and the greater the dip angle of the interlayer, the fewer the number of wing cracks required for specimen failure and the lower the degree of wing crack development. The increase in interlayer thickness and dip angle resulted in a specimen structure that was more susceptible to damage. The actual crack initiation angles agree with the theoretically calculated angles based on the maximum tensile stress theory. These findings emphasize the critical role of these parameters in influencing the failure mode of rocks.

Determination of heat transfer representative element volume and three-dimensional thermal conductivity tensor of fractured rock masses

The natural fracture system exerts a significant influence on the physical and mechanical properties of rock masses. The heat transfer in fractured rock masses is much more complicated than that of intact rock due to the thermal contact resistance induced by natural fractures with varying size, aperture, roughness, and orientation. This work describes a method for determining the representative element volume (REV) of heat transfer and the 3D thermal conductivity tensor of fractured rock masses. The method is based on the element-wise averaging of temperature and heat flux, which can be obtained from a finite element solution to a steady state heat transfer problem with specific boundary conditions. A case study was conducted based on the geological data of a potential area for high level radioactive waste disposal in China. The results indicate that the size of heat transfer REV of the rock masses in the study area is approximately 18 m × 18 m × 18 m. 3D thermal conductivity tensor, the magnitudes and directions of the three principal thermal conductivities, and anisotropy of the fractured rock masses were obtained. Influences of main fracture parameters including density, disc diameter, and thermal contact resistance on the heat transfer characteristics were investigated. The research results in this work can provide a better understanding of the discontinuous heat transfer processes in fractured rock masses and their homogenization methods.

Mechanical properties and constitutive model of fractured red sandstone under acid corrosion

Red sandstone was selected for the study and specimens were prepared at 0°, 30°, 45° and 60° fracture inclinations and maintained in an acid solution at pH = 2. The specimens were subjected to uniaxial compression tests before and after maintenance to obtain the mechanical parameters and to observe the damage properties of the specimens. Based on the Lemaitre strain equivalence principle, a macroscopic fracture model for single-fissure rock masses and a statistical damage model for the Weibull distribution of micro-fissures were combined to derive macro-and micro-coupled damage variables for the specimens. The damage variables after acid solution corrosion are considered to derive the constitutive model for fractured red sandstone containing fractures after acid corrosion. The theoretical damage constitutive curves were compared with the experimental curves to analyse the applicability of the constitutive equation. The results show that the peak stress, peak strain and elastic modulus of the fractured specimens all vary regularly with the inclination angle, first decreasing and then increasing with the increase in the inclination angle; the peak compressive strength and elastic modulus of the fractured sandstone all tend to decrease and the peak strain tends to increase after corrosion by acid solution; the damage characteristics of the fractured sandstone are more influenced by the inclination angle and less influenced by acid corrosion; by comparing the theoretical curve with the experimental curve, the established damage constitutive model is in good agreement at the elastic deformation and plastic yielding stages. The mechanical properties of rock masses with different inclinations of fracture are quantified on the basis of the test results. The damage characteristics of rock masses with different fracture inclinations under normal and acid corrosion conditions are studied. The macro- and micro-coupled damage variables of fractured rock masses under acid corrosion are derived and validated.

A new shear creep damage model for rock masses after considering initial damage.

For a long time, one of the important safety problems in open-pit mines is the stability of a large number of high slopes with gently inclined soft interlayer. Rock masses formed after long geological processes generally have some initial damage. Mining works also cause varying degrees of disturbance and damage to rock masses in the mining area during the mining process. This phenomenon means that accurate characterization of the time-dependent creep damage for rock masses under shear load is necessary. The damage variable D is defined based on the spatial and temporal evolution laws of shear modulus and initial level of damage for the rock mass. In addition, a coupling damage equation between the initial damage of the rock mass and shear creep damage is established based on Lemaitre's strain equivalence assumption. Kachanov's damage theory is also incorporated to describe the entire process of time-dependent creep damage evolution for rock masses. A creep damage constitutive model that can reasonably reflect the actual mechanical properties of rock masses under multi-stage shear creep loading conditions is established. This takes into account multi-stage shear creep loading conditions, instantaneous creep damage during the shear load phase, staged creep damage and factors influencing the initial damage of rock masses. The reasonableness, reliability and applicability of this model are verified by comparing the results of the multi-stage shear creep test with calculated values from the proposed model. As opposed to the traditional creep damage model, the shear creep model established in this present study takes into account the initial damage of rock masses and can describe the multi-stage shear creep damage characteristics of rock masses more convincingly.

Experimental study on shear failure modes and acoustic emission characteristics of rock-like materials containing embedded 3D flaw

In nature, rock mass usually contains natural defects, which affect the mechanical properties of rock mass. At the same time, the failure of rock mass is often accompanied by shear failure behavior. Therefore, it is great significance to monitor and predict the shear failure process of fractured rock mass in order to ensure the stability of structure and the safety of construction. In this study, a method for making rock-like samples containing embedded 3D flaw is proposed and a series of shear tests are carried out under different normal stresses. The test results show that the complex shear stress-shear displacement curve can be divided into four stages. The shear strength, residual strength and shear modulus of the specimens are affected by the flaw dip angle and normal stress. The tensile failure mode is more likely to occur in low stress and small flaw angle specimens, while the shear failure mode mainly occurs in high stress specimens. A sudden increase in AE counts, AE event rates, and a sudden decrease in b-value to a minimum are usually precursors to rock failure. The RA/AF value can accurately reflect the classification and development of rock tension shear cracks. Through the Kernel density estimation (KDE) analysis on the distribution of AE events, the damage locations of rock-like in each stage are effectively identified. The movement of the maximum density point is consistent with the rock crack propagation tendency, almost following the uniform diffusion of the specimens from the middle to the end.

Effects of High Temperature Treatments on Strength and Failure Behavior of Sandstone under Dynamic Impact Loads

With the increasing demand for resource consumption, the mining depths gradually increase, resulting in increases of temperature at tens or even hundreds of degrees. High temperature could damage to interior structures and alter the mechanical properties of rock mass. Therefore, studying the effects of temperature on dynamic mechanical properties and failure behaviors are of great significance for deep resources exploitation. In this study, to study the effects of high temperature treatment on the strength and failure behavior of typical sandstones, specimens were prepared and heated to different degrees. The longitudinal wave velocity, volume, and density of specimens before and after high-temperature treatment were examined. Then, the Thomas Hopkinson (SHPB) test was conducted on specimens with different air pressures and the dynamic stress-strain curve, peak stress, peak strain, and other dynamic characteristics were obtained. The variations regulations and failure behavior of sandstone under the effects of high-temperature treatments and different impact loads were analyzed and discussed from the aspects of stress-strain, peak strength, and peak strain. It was observed that with the increase of heating temperature, the average density, average wave velocity, peak strength, and average elastic modulus of the sandstone specimens all showed a decreasing trend and the highest decreasing rated occurred at the temperature between 600 °C and 800 °C. The obtained results provided a certain theoretical basis for deep mine exploitation, especially for mines with high temperature.