Rock-like Samples Research Articles

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.

A hybridized DDA-DDM for modeling jointed rock masses

The complexity of geo-materials’ behaviors surpass the capabilities of conventional numerical methods alone, particularly when realistically modeling rock structures. Coupling methods can enhance the realism of numerical modeling. Discontinuous deformation analysis (DDA) and displacement discontinuity method (DDM) are combined to model block displacement and crack propagation mechanisms in a blocky rock mass. DDA calculates stresses, strains, rotations, and displacements of the blocks, while DDM predicts crack propagation paths based on specified boundary conditions. The displacements result from DDA are transformed into stresses, followed by investigating crack propagation mechanisms within each block using Kelvin's solution. Boundary stresses are adjusted as cracks propagate, updating stress boundary conditions in DDA. This iterative process continues until crack propagation halts or a new block emerges. In this paper, the complete failure process of a rock slab with one pre-existing non-persistent joint located on the crest of a rock slope and compression test on the rock-like specimen with a single random crack with a 45° slope angle is simulated using the proposed numerical approach. The proposed numerical solution is compared with existing numerical results. This comparison confirms the accuracy and effectiveness of the proposed procedure, as the predicted crack propagation paths from the coupled numerical method align well with the corresponding numerical results from the rock-like samples.

Mechanical and energetic properties of rock-like specimens under water-stress coupling environment

AbstractSoft rock has the properties of low strength, poor integrity, and difficulty in core extraction. In order to study the deformation and failure of soft rock, this study used fine river sand as aggregate, cement and gypsum as bonding materials, and borax as a retarder to produce cylindrical rock-like samples (RLS) with a sand cement ratio of 1:1. Uniaxial compression tests were conducted on RLS under DIT (different immersion times) (0, 4, 8, 12, 24, and 48 h) in the laboratory. The mechanical and energy properties of RLS under water-stress coupling were analyzed. The results showed that the longer the IT of the RLS, the higher their water content (WC). As the moisture time increases, the uniaxial compressive strength, elastic modulus (EM), and softening coefficient (SC) of the sample gradually decrease, while the rate of change of EM is the opposite. The fitted sample SC exhibits a good logarithmic function relationship with WC. During the loading process of the sample, more than 60% of the U (total energy absorbed) during the loading process of the sample is accumulated in the form of Ue (releasable elastic energy), while less than 40% of U is dissipated by the newly formed micro cracks during the compaction, sliding, and yield stages of the internal pores and cracks of the sample. The U before the peak and the Ue of the RLS decrease exponentially with the moisture content; the relationship curves of Ue/U (released elastic energy ratio) and Ud/U (dissipated energy ratio) of RLS during uniaxial compression with the σ1/σmax (axial stress ratio) can be divided into three stages of change, namely the stage of primary fissure compaction and closure (σ1/σmax < 0.25), continuously absorbing energy stage (0.25 < σ1/σmax < 0.8), and energy dissipation stage (σ1/σmax > 0.8); the D (damage variable) was defined by the ratio of Ud (dissipated energy) to the Udmax (maximum dissipated energy) at failure time of RLS, the fitting of the relationship between the damage variable and axial strain conforms to the logistic equation.

Investigations into size dependence on the behavior of rocks with a “V” notch and hole under uniaxial compression

This study employed a combination of experimental analysis and numerical simulations using the Particle Flow Code (PFC2D) to investigate the impact of interaction between porosity and V-shaped notch on the breakage behavior of gypsum-based rock-like samples. Also, the influence of scale effect on the notch-hole interaction has been investigated while the “<” notches were positioned at three different orientations (0°, 45°, and 90°) relative to the X-axis. Parallel to the experimental phase, nine samples with analogous “<” shape notches, as well as nine additional models featuring different “>” shape notches, were generated and assessed through numerical simulations. The findings indicate that crack propagation was primarily governed by the notch shape, asymmetric line angle, and model dimensions. Notably, the rock bridge located between the “<” shape notch and the hole exhibited significantly greater breakage compared to other notch configurations (i.e., “>” shape notch). Moreover, the volume of damage increased with the inclination of the asymmetric line and the model's dimensions. Both the angle of the asymmetric line and the model's size contributed to enhanced sample strength. Elevating the asymmetric line angle, simulation size, and V-shaped notch led to the creation of more fractures, consequently resulting in a heightened occurrence of failure events in rock-like materials. Delay failure occurred in models containing “>” shaped notch while abrupt failure occurred in models containing “<” shaped notch. The experimental results affirm that PFC2D faithfully replicated the sample's failure pattern and strength. This study is useful for rock engineering design when delay failure and or abrupt failure threaten the stability of rock engineering structures.

Physical Simulation of Brittle Rocks by 3D Printing Techniques Considering Cracking Behaviour and Permeability

Additive manufacturing, commonly named 3D printing, is more frequently studied and used due to its ability to replicate micro- and macroscopic structures in natural rocks and fabricate complex experimental samples. Previous studies in this field mainly focused on mechanical properties and cracking behaviour but less on permeability because of the difficulties in unifying these three aspects with modern 3D printing techniques. Since the plaster-based 3D printing (PP) samples are more brittle and are close to rocks, and the stereolithography (SLA) samples have a higher resolution without chemical reaction with water, the present study combined these two mainstream 3D printing methods to try to replicate both the mechanical and permeable behaviour of rocks. Stereolithography (SLA) resolution can replicate submillimetre pores and structures in natural rocks. The result is that the PP method can successfully print rocklike samples, and their strength and failure modes are significantly influenced by the printing dip angle and sintering temperature. The porosity and anisotropy of the permeability of the samples printed by the SLA method are compared with the prototype porous basalt, and the replication ability in pore structures and seepage is confirmed. In addition to the experimental study, the theoretical permeability of samples printed with various resolutions is also discussed. The results of this study demonstrate the effectiveness of combining PP and SLA 3DP techniques for physically simulating natural porous rocks.

Experimental Investigation on the Destruction Features and Acoustic Characteristics of a Brittle Rock Sample Containing Both 2D and 3D Preset Flaws

Original fracture structures always present discontinuity in the real rock mass, and many invisible fractures hide inside the rock mass, which may cause serious engineering safety issues. To mimic the true 3D fracture structures through the experimental method, the gypsum rock-like samples containing both 2D through-type and 3D internal-type preset flaws are prepared, and multiple sets of inclination angles of the twin parallel flaws are set in the test. By applying the AE and DIC monitoring technologies during the uniaxial compression tests, the main results are as follows: (1) The flaw inclination angle presents a direct influence on the surface cracks distribution, maximum principal strain field, and the density of secondary failure in the middle rock; (2) AE events initially distribute around the internal 3D preset flaw, while the gradient inclination angle shows a slight impact on the events’ location before reaching the UCS status of samples; (3) mutations in b-values and S values can serve as evidence for predicting local damage, and the final failures quickly form at various scales and energy levels; (4) when the statistical analysis grid is divided sufficiently, the data window width and moving step length have little impact on the evaluation results, while the recommended bin width of event magnitude is 0.5 or 1.0.

Influences of true 3D twin flaws on principal stress status and crack occurrence of brittle rock-like samples under uniaxial compression: Insights from experimental and DEM studies

Fracture structures commonly have negative impacts on the strength and safety of rock mass, and various combinations of 2D and 3D flaws make the destruction procedure becomes more complicated. Therefore, laboratory tests based on three types of flawed rocks (symmetric twin flaws with different 2D-3D occurrences) are finished to detect the mechanical, optical and acoustic characteristics of fractured rocks during the uniaxial compression test; PFC3D simulations are conducted for analyzing the deformation features, principal stress distributions, and detailed failure mechanism of the fractured rocks. The main results are as follows: 1) Different combinations of 2D & 3D preset flaws directly influence the results of deformation, stress distribution, and failure developments. 2) Rotation of the intermediate stress axes only appear near the flaw inclination boundary (when the monitoring position moves outwards), while the directions of intermediate principal stress axes remain stable near the flaw strike boundary. 3) Separating cracks by various occurrences helps to construct local failures along different directions, and make some local failures visible and clear; the traditional cracks (short line or thin oval shape) are induced by the uneven deformation in x-o-z planes, and the separated cracks (wide oval or standard disc shape) result from the uneven deformation in y-o-z planes. 4) Surrounding rocks at different positions suffer various modes of failures, the non-ignorable thickness of preset flaw leads to simultaneous Mode I and Mode II failure at the flaw tip, and the mixed Mode II&III failure only occurs in the rocks adjacent to the flaw strike boundary.

Failure mode of parallel-fractured rock-like sample with different inclinations

Parallel fractures, a kind of common geological defect in natural rock mass, show a variety of failure mechanism and increases the difficulty in the timely warning of geological disasters such as landslide. Therefore, studying the mechanical properties and failure mechanism of parallel-fractured rock mass occupies a vital position in the stability analysis and warning technology of disaster precursor. In response to this, the laboratorial efforts on micro fracture mode and macro strength prediction of parallel-fractured rock-like samples with different inclinations were made in this paper. Firstly, the parallel-fractured samples were prepared by changing the fracture parameters, and the uniaxial compression test was then carried out. According to the mechanical parameter variations of samples during axial loading, the multiple indexes affecting the uniaxial compressive strength of parallel-fractured samples was clarified, and the specific influence of fracture inclination was quantified by mathematical method. Finally, the progressive failure mechanism of samples was analyzed through strain field evolution in virtue of digital image correlation (DIC) technique, and the main failure modes of parallel-fractured samples were summarized. Meanwhile, the acoustic emission (AE) signals were collected and processed to further reveal the failure characteristics of parallel-fractured samples with different inclinations in a microscopical perspective.

Mechanical behavior and failure mechanism of composite layered rocks under dynamic tensile loading

To bolster the safety and efficacy of blasting and impact drilling for underground works in composite rock strata, the dynamic tension of composite rocks requires thorough examination. Given the challenges of composite rock sampling, cement mortars with varying mix ratios are utilized to create composite rock-like test blocks. These blocks are composed of two different strength materials, further processed into differently sized experimental samples as required. Using a split Hopkinson pressure bar (SHPB) test device, we conducted dynamic Brazilian splitting tests at varying incident angles α (the angle between the incident wave direction and the bedding plane) and strain rates on these composite rock-like samples. The modes of crack propagation in some samples were recorded with a high-speed camera. Laboratory tests and PFC2D simulation were used to analyze the dynamic tensile mechanical properties and failure mechanisms of composite rock samples. Findings indicate the dynamic tensile strength of a composite rock sample is governed by the bedding plane inclination angle. As the incident angle rises from 0° to 90°, the dynamic tensile strength of the composite rock sample first decreases, then increases, consistently reaching a minimum value at α = 30°. The damage model of composite rock samples is also influenced by the dip angle of the bedding planes. At α = 0°, the composite rock sample exhibits through-cracks along the incident wave direction and splitting tensile damage is observed. As α increases, the failure mode gradually transitions from splitting tensile damage to a combination of tensile and shear slip damage along the bedding. Tensile damage always manifests in materials of lower strength. When α surpasses 45°, the failure mode reverts from combined damage to splitting tensile damage. Cross-sectional tensile stress clouds generated by PFC software demonstrate that the tensile stress contours at the specimen's center are elliptically distributed, with the ellipse's long axis nearly parallel to the bedding plane.

Shear mechanical properties and energy evolution of rock-like samples containing multiple combinations of non-persistent joints

Shear mechanical properties and energy evolution of rock-like samples containing multiple combinations of non-persistent joints

Identifying rock fracture precursor by multivariate analysis based on the digital image correlation technique

Estimating the initiation and propagation of rock fractures and identifying fracture precursors are significant for rock failure analysis. This study performed numerical uniaxial compression tests of rock samples with an excavated hole and laboratory tests of rock-like samples. Statistical methods were used to analyze the precursory indices of full-field strain information based on digital image correlation (DIC) technology. An identification method for rock fracture initiation based on the absolute standard deviation (ASD) and absolute variation coefficient (AVC) of the strain field was proposed. The results indicated that a sudden change in the shear strain field during the loading process was closely related to the occurrence of internal cracks in the rocks. The variation laws of the ASD and AVC of the strain field were highly correlated with the rock fracture evolution. The progress in the variation rate of the strain field corresponded to the rock fracture evolution, and the change points can be used as precursors of the rock fracture. The precursory points of the excavated and rock-like samples in each crack propagation stage were at least 0.84% and 1.06% earlier than those of the current stage, respectively. The precursory points of each stage were 2.48% and 2.11% earlier than those of the final failure stage. The first precursory points were 45.45% and 42.11% earlier than the final failure time.

Fracturing evolution and strain characteristics of layered rock-like materials with rough interfaces

Layered rock-like samples containing saw-tooth interfaces of various joint roughness coefficients (JRC) and included angles were conducted uniaxial compression with the loading rate of 0.005 mm/s. The peak stress declines from 38.36–39.90 MPa to 17.35–30.67 MPa for included angle = 15°–60°, and then increases to 24.30–33.83 MPa for 60°–75°, but the peak strain decreases by 22.39%–41.30%. For JRC = 0–19.55, mechanical properties of samples are enhanced, while the anisotropy weakens. When the included angle is small (15°, 30°), the layered samples show a typical tensile splitting failure crossing the weak interlayers. For a large included angle of 45°–75°, failure modes are featured by shear sliding along weak interlayers combined with tensile splitting. As JRC increases, fracturing mechanism transition from shear sliding to mixed tension shear failure then to tensile splitting can be identified. With an increase in JRC or included angles, the global lateral strain of samples in plastic deformation stages changes from “sudden increase” to “progressive increase” to “jump increase”. For included angle = 15°, the layered sample produces dramatic lateral local strain at the weak interlayers due to tensile splitting failure. For included angle = 45°, both axial and lateral local strains at the weak interlayers show an obvious increase at the main shear failure surface. For a large included angle of 75°, the lateral local strain remarkably increases at the weak interlayers along with tensile failure of samples.

Crack Initiation and Propagation of Embedded Three-Dimensional Parallel Cracks in Transparent Rock-Like Material

Abstract In order to understand the initiation and propagation of three-dimensional (3D) embedded parallel cracks in brittle rock under uniaxial and biaxial compression, a preparation method of a transparent rock-like material was proposed in order to observe the propagation process of cracks in brittle rock. Uniaxial and biaxial compression tests were carried out on the transparent rock-like samples containing two embedded 3D parallel cracks. Four types of crack propagation modes were observed: wing crack, petaloid crack, flat-wing crack, and ring-like crack. It is also found that the direction of lateral pressure relative to the strike of the embedded crack has a significant effect on the propagation direction of new generated cracks: a lateral pressure parallel to the strike of the embedded cracks promotes crack propagation in the direction of the maximum principal stress; on the other hand, a lateral pressure normal to the strike of the embedded cracks promotes cracks propagation around the embedded crack at an angle of 30°–60°, forming ring-like cracks, which is similar to the zonal disintegration phenomenon monitored around deep underground excavations.

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.

Deterioration laws of Hoek-Brown parameters in freeze–thaw multi-fractured rock mass

The Hoek-Brown criterion can better depict the nonlinear failure characteristics of rock mass, which has been widely used in the fields of large-scaled slopes, deep-buried tunnels, foundations in complex geological conditions, hydropower dams, and energy mining. In view of the previous studies mostly focused on the property reduction of freeze–thaw rock, the deterioration study of Hoek-Brown parameters for freeze–thaw multi-fractured rock mass was investigated in this study. Firstly, Monte-Carlo method was used to generate two-dimensional discrete fracture network, according to which the multi-fractured rock-like samples were prepared. Freeze-thaw cycle experiments were subsequently designed and executed to observe the apparent damage of freeze–thaw effect on the samples. Then, laboratory direct shear tests on freeze–thaw samples under multistage normal loading were carried out. The shear performances of freeze–thaw rock mass were analyzed based on the shear stress-shear displacement curves of samples with different freeze-thawed cycles. Besides, considering the deficiencies of the existing Hoek-Brown parameter estimation methods such as complicated sample preparation and strong subjectivity, a new estimation method based on shear test was proposed by deducing the shear expression of Hoek-Brown criterion, which was programmed in MATLAB and verified by direct shear test results. On this basis, the values of Hoek-Brown parameter of those samples under different freeze–thaw cycles were determined, and the variation law with freeze–thaw cycles was summarized. It turned out that the values of GSI and mi both decrease with the increase of freeze–thaw cycles, and the decreasing rate is also lowering, according with the negative exponential function model.

Simulation Study on Crack Initiation and Energy Mechanisms of Rock-like Samples with Non-Parallel Overlapping Flaws under Uniaxial Compression

Non-parallel overlapping flaws widely exist in engineering rock mass. Understanding their crack initiation and energy evolution characteristics is of great significance to ensure the stability of rock engineering. Based on the existing experiments, the influence of flaw inclination angles (β) on the crack initiation and energy evolution characteristics of rock samples with non-parallel overlapping flaws was studied by numerical simulation. The results show that (1) the uniaxial compressive strength, elastic modulus and crack initiation stress increase with the increase of flaw angle. (2) The boundary energy, strain energy and dissipated energy under peak stress increase with the increase of flaw angle; the dissipated energy increases the most. (3) With the increase of flaw angle, the tension stress zone is transferred to the flaw tip, and the zone is reduced gradually; the maximum tensile stress and the tension stress concentration decrease. (4) In the crack initiation stage, the influence of a lower flaw inclination angle (β ≤ 60°) on the lateral displacement field of the sample is higher than that of a high flaw inclination angle (β = 75°).

Deformation and failure mechanism of horizontal soft and hard interlayered rock under uniaxial compression based on digital image correlation method

The deformation of bottom rock masses surrounding a tunnel may lead to floor upheaval, structural damage and track irregularity during operation when the tunnel is constructed in soft and hard interlayered rock strata with gently dipping layers. Therefore, in order to study the deformation behavior of soft and hard interlayered rock, a special metal mold was designed to restrain the displacement of a certain side of the samples for the uniaxial compression test. A series of soft and hard interbedded rock-like samples with different height-length ratios were prepared. The deformation characteristics and failure properties of horizontal soft and hard interbedded rock-like samples were studied under uniaxial compression. The test results show that the peak uniaxial compressive strength of the horizontal soft and hard interbedded rock-like samples decreases with the increasing of the height-length ratios. The failure of the horizontal soft and hard interlayered rock-like samples is a process of coupling failure of the soft layer material and the hard layer material under compressive stress. The failure process of the sample is dominated by axial splitting and buckling. Based on the digital image correlation (DIC) technology, the relationship between the displacement and stress of the sample was analyzed. Under the same stress value, the displacement of the outer layer is greater than that of the inner layer. The strain and the displacement of the soft rock layer are greater than those of the hard rock layer. The test results are consistent with the engineering reality and explain well the mechanism of the soft and hard interlayered surrounding rock lifting at the bottom of the tunnel.

Experimental and numerical investigation on compressive strength and crack behavior of rock-like specimens with open flaws under confining loads

Engineering problems are related to the failure of geological material, especially that of jointed rock masses. To investigate the influence of confining stress and inclination angle β on cracking behavior and failure mechanism, triaxial compression tests are conducted on rock-like samples containing parallel opening flaws. There are two patterns, namely, tensile failure and tensile-shear failure, and each occurrence has an equal frequency. Nine crack modes are summarized, and the most special one is mode 8, which is mainly observed in samples with β = 60° at high confining pressure. Both the compressive strength and internal friction in samples with β = 60° are the smallest in the experiments, and those in samples with β = 65.31° based on the improved theory are the smallest. The compressive strength decreases with the increase of inclination angle β when 0°≤β≤60°; however, it increases as inclination angle β increases when 60°&amp;lt;β≤90°. This phenomenon is found in laboratory experiments and numerical tests and is almost even in accordance with theoretical results. Numerical compression tests are performed to investigate the influence of the width-to-length ratio of opening flaws on compressive strength and to verify the improved theory reliability. Compared numerical results with the two kinds of theoretical results, the width-to-length ratio has an obvious impact on compressive strength and the opening fracture intensity factor KⅠ.

Acoustic emission and failure characteristics of cracked rock under freezing-thawing and shearing

The acoustic emission (AE) signal characteristics and deformation characteristics of cracked rocks under shear load can characterize the degree of rock degradation under freeze–thaw (F-T) cycles. Understanding these characteristics is of great significance for preventing rock mass engineering disasters in cold regions. In view of this, the effects of F-T cycles and crack inclination angle β on rock shear characteristics were studied by carrying out F-T tests and direct shear tests of rock-like samples with different crack inclination angles. Then, combined with AE technology and digital image correlation (DIC) technology, the effects of F-T cycle and crack inclination angle β on the characteristics of AE signals and shear deformation failure characteristics at each stage of the shearing process were analyzed. The research results show that: the deterioration of shear properties mainly occurs during the first 10 cycles. The cohesion and internal friction angle of the samples are the smallest at 30° and 60°, respectively, and the shear strength is the smallest at 60°. The damage degree of F-T cycle to the cracked samples at different angles is different. The damage degree of the 0° inclination single-cracked sample is the largest, reaching 57.17%, and the 90° sample is the smallest, reaching 49.43%. The count and b-value features of AE indicated that F-T cycles attenuated the differences in AE signal features at various stages of the shearing process. When the number of F-T cycles is less than 5, the b-value of AE undergoes a change process of a small and slow rise, a small slow decrease, a sharp decrease, and an oscillating change. When the F-T cycle reaches 20 times, the AE count and b-value characteristics did not change significantly. The speckle results show that when the normal stress is 1.5 MPa, the failure mode of the sample under shear load is pure shear or tensile-shear failure. With the increase of the number of F-T cycles, the sample has a large strain area increases and tends to fail along the shear plane.

Experimental Study on the Damage Characteristics and Fracture Behaviour of Rock-like Materials with Weak Interlayer Zones

To study the effect of the dip angle of the weak interlayer zone (WIZ) on the damage characteristics and fracture behaviours of rock-like samples, a series of uniaxial compression tests were conducted, accompanied by acoustic emission (AE) tests and the digital speckle correlation method (DSCM). The experimental results indicate that the stress—strain curves before the peak can be divided into plastic—elastic—plastic and elastic—plastic curves, and the stress—strain curves after the peak can be divided into plastic failure, transitional failure and brittle failure curves. The relationship between the peak stress and peak strain and WIZ angle can be well described by two linear functions. As the angle increased, the specimen gradually changes from tensile failure to shear failure, and the number of cracks and falling fragments decreases gradually. In addition, it becomes difficult to predict rock mass failure by AE when the WIZ angle is close to 60°. The AE counts decrease with an increasing angle, reach a minimum at 60°, and then increase. Furthermore, the WIZ plays a key role in the deformation of upper hard rock.