Experimental study and numerical simulation of uniaxial compression on artificial rock samples with Z-shaped fractures

2021 ◽  
Author(s):  
Tao Zhou ◽  
Haijun Chen ◽  
Liangxiao Xiong ◽  
Zhongyuan Xu ◽  
Jie Yang ◽  
...  
Keyword(s):  
Elastic Modulus ◽  
Crack Length ◽  
Uniaxial Compression ◽  
Inclination Angle ◽  
Failure Surface ◽  
Peak Strength ◽  
Particle Flow Code ◽  
Compression Tests ◽  
Failure Characteristics ◽  
Change Trend

Abstract To study the influence of the inclination and length of Z-shaped fissures on the mechanical properties and failure characteristics of the rock mass, this study conducts a series of uniaxial compression tests on rock-like materials with prefabricated Z-shaped fractures. In addition, two-dimensional Particle Flow Code software is used to perform uniaxial compression numerical simulations. The results show that when the specified inclination angle γ (γ = 0°, 30° or 45°) of the parallel cracks on both sides remains unchanged, the peak strength and elastic modulus of the sample show an M-shaped change trend with an increase in the inclination angle β of the middle connection crack. When γ = 60° or 90°, however, the peak strength and elastic modulus of the sample show a trend of decreasing, increasing, and then decreasing as β increases. In addition, the peak strength and elastic modulus of the sample decrease with an increase in the crack length. The influence of crack length on the elastic modulus is less than that of compressive strength. Further, the main failure mode of specimens with Z-shaped cracks is determined to be tension–shear mixed failure manifested by crack propagation from the tip of the prefabricated crack to the upper and lower boundaries of the sample. As a result, a through failure surface is formed with the prefabricated crack, which destroys the sample.

scholarly journals Experimental and Numerical Investigation of Failure Characteristics and Mechanism of Granites with Different Joint Angles

2021 ◽  
Vol 2021 ◽  
pp. 1-10
Author(s):  
Zhenhua Wang ◽  
Jun Fang ◽  
Gang Wang ◽  
Yifan Jiang ◽  
Dongwei Li
Keyword(s):  
Elastic Modulus ◽  
Uniaxial Compression ◽  
Elastic Strain Energy ◽  
Peak Stress ◽  
Peak Strength ◽  
Particle Flow Code ◽  
Dissipated Energy ◽  
Shear Cracks ◽  
Compression Tests ◽  
Dip Angle

The uniaxial compression tests were conducted on granite samples with different joint dip angles to more favorably explore the influences of the nonconsecutive joint on mechanical properties and deformation characteristics of the rock mass. The stress-strain curves, deformation and strength characteristics, and energy evolution process of the samples were analyzed. Numerical simulation using particle flow code (PFC) is employed to study the crack propagation process. The mode of jointed and fractured rock was investigated. The research results showed a significant reduction in both the peak strength and elastic modulus of jointed samples compared with intact ones: the peak strength and elastic modulus drop to the minimum at the joint dip angle of about 45°, especially for the peak strength, which takes up about 55% of the intact samples. The fractured samples’ total energy, elastic strain energy, and dissipated energy during the uniaxial compression drop significantly relative to intact samples. The proportion of the fracture modes varies with different joint dip angles, in which the ratio of shear cracks grows at first and then declines, with the highest balance at the dip angle of 45°. The damage stress’s sensitivity to the dip angle change is greater than that of the peak stress, with reduction amplitude more extensive than the latter.

scholarly journals Experimental study on the influence of locked-in stress on the uniaxial compressive strength and elastic modulus of rocks

2020 ◽  
Vol 10 (1) ◽  
Author(s):  
Xin Liu ◽  
Hansheng Geng ◽  
Hongfa Xu ◽  
Yinhao Yang ◽  
Linjian Ma ◽  
...  
Keyword(s):  
Mechanical Properties ◽  
Elastic Modulus ◽  
Uniaxial Compression ◽  
Testing Machine ◽  
Peak Strength ◽  
Test Block ◽  
Compression Tests ◽  
Inclusion Content ◽  
Rubber Particles ◽  
Ground Stress

Abstract The rock contains many inclusions which produce high locked-in stress under the ground stress. In order to study the influence of locked-in stress on the mechanical properties of rocks, the rock-like materials and nitrile rubber particles are used to make a test block of the rock-like model which contains inclusions. The rubber particles will expand as the test block is heated, which creates locked-in stress in the inclusions. Uniaxial compression tests of similar model blocks with different locked-in stresses and different inclusion contents were performed by using a water bath and MTS-5T uniaxial compression testing machine. The results show that the peak strength and elastic modulus decreased with the increasement of locked-in stress and inclusion content. In the meantime, the relationship among the peak strength, the elastic modulus of the test piece, the locked-in stress and the inclusion content were obtained with the help of a mathematical fitting analysis of the quantitative formula. Furthermore, the expression and value curve of the joint impact factor are calculated. This paper evaluates the importance of the locked-in stress in the mechanical properties of the rock-like material and provide a guide for other researchers to further investigate the locked-in stress in rocks.

scholarly journals Discrete Element Modeling on Mechanical Behavior of Heterogeneous Rock Containing X-Shaped Fissure under Uniaxial Compression

Geofluids ◽  
2020 ◽  
Vol 2020 ◽  
pp. 1-14
Author(s):  
Ming Chen ◽  
Jian Liu ◽  
Zhengyong Xie ◽  
Jianjun Liu ◽  
Xunjian Hu ◽  
...  
Keyword(s):  
Elastic Modulus ◽  
Crack Initiation ◽  
Mechanical Behavior ◽  
Failure Mode ◽  
Uniaxial Compression ◽  
Inclination Angle ◽  
Acute Angle ◽  
Peak Strength ◽  
Discrete Element Modeling ◽  
Initiation Stress

Based on the experimental results of an intact rock specimen under uniaxial compression, particle flow code (PFC2D) was adopted to carry out a discrete element modeling (DEM) for the mechanical behavior of heterogeneous rocks containing X-shaped fissures (two intersecting symmetric single fissures) under uniaxial compression. The influences of β (the acute angle between two single fissures) and the direction angle α (the acute angle between the bisector of β and perpendicular to the loading direction) on the strength, deformation, energy, crack propagation, and ultimate failure mode were analyzed in detail. Numerical simulated results showed the following: (1) Due to the X-shaped fissures, not only the peak strength, elastic modulus, crack initiation stress, and damage stress were significantly reduced, and the reduced degree of the peak strength was obviously greater than that of the elastic modulus, but also the brittleness and energy were significantly weakened. (2) The peak strength and elastic modulus generally decreased with the increase of β and increased with the increase of α . Moreover, the change trends of crack initiation stress, damage stress, boundary energy, and total strain energy at the peak stress were consistent with the peak strength. (3) Regardless of the changes of α and β , models all firstly initiated wing cracks at the two tips of the single fissure with a larger inclination angle, and the crack initiation angle decreased with the increase of the inclination angle of the single fissure. (4) The fracture was dominated by tensile microcracks, and no microcracks were generated in a certain range of the X-shaped fissure center. The failure mode was mainly split along the axial direction, and the failure surface started from the tips of the fissure and extended to both ends of models. (5) The uniaxial compressive strength and elastic modulus increased exponentially with the increase of the homogeneity factor. When the homogeneity factor was small, the microcracks were more evenly distributed in the models; when the homogeneity factor was large, the microcracks were mainly concentrated at the tips of the fissure in the models. This study can provide some references for the correct understanding of the mechanical properties of rock masses containing X-shaped fissures.

scholarly journals Acoustic Emission Characteristics and Joint Nonlinear Mechanical Response of Rock Masses under Uniaxial Compression

Energies ◽  
2021 ◽  
Vol 14 (1) ◽  
pp. 200
Author(s):  
Zhongliang Feng ◽  
Xin Chen ◽  
Yu Fu ◽  
Shaoshuai Qing ◽  
Tongguan Xie
Keyword(s):  
Acoustic Emission ◽  
Uniaxial Compression ◽  
Inclination Angle ◽  
Failure Modes ◽  
Strain Curve ◽  
Particle Flow Code ◽  
Rock Masses ◽  
Physical Experiments ◽  
Inclination Angles ◽  
Joint Inclination

The joint arrangement in rock masses is the critical factor controlling the stability of rock structures in underground geotechnical engineering. In this study, the influence of the joint inclination angle on the mechanical behavior of jointed rock masses under uniaxial compression was investigated. Physical model laboratory experiments were conducted on jointed specimens with a single pre-existing flaw inclined at 0°, 30°, 45°, 60°, and 90° and on intact specimens. The acoustic emission (AE) signals were monitored during the loading process, which revealed that there is a correlation between the AE characteristics and the failure modes of the jointed specimens with different inclination angles. In addition, particle flow code (PFC) modeling was carried out to reproduce the phenomena observed in the physical experiments. According to the numerical results, the AE phenomenon was basically the same as that observed in the physical experiments. The response of the pre-existing joint mainly involved three stages: (I) the closing of the joint; (II) the strength mobilization of the joint; and (III) the reopening of the joint. Moreover, the response of the pre-existing joint was closely related to the joint’s inclination. As the joint inclination angle increased, the strength mobilization stage of the joint gradually shifted from the pre-peak stage of the stress–strain curve to the post-peak stage. In addition, the instantaneous drop in the average joint system aperture (aave) in the specimens with medium and high inclination angles corresponded to a rapid increase in the form of the pulse of the AE activity during the strength mobilization stage.

scholarly journals Energy Dissipation-Based Method for Strength Determination of Rock under Uniaxial Compression

2020 ◽  
Vol 2020 ◽  
pp. 1-13 ◽  
Author(s):  
M. M. He ◽  
F. Pang ◽  
H. T. Wang ◽  
J. W. Zhu ◽  
Y. S. Chen
Keyword(s):  
Yield Strength ◽  
Uniaxial Compression ◽  
Peak Strength ◽  
Dissipated Energy ◽  
Compression Tests ◽  
Dissipation Energy ◽  
Evolution Characteristics ◽  
Deformation Properties ◽  
Energy Coefficient ◽  
The Stability

The energy conversion in rocks has an important significance for evaluation of the stability and safety of rock engineering. In this paper, some uniaxial compression tests for fifteen different rocks were performed. The evolution characteristics of the total energy, elastic energy, and dissipated energy for the fifteen rocks were studied. The dissipation energy coefficient was introduced to study the evolution characteristics of rock. The evolution of the dissipation energy coefficient for different rocks was investigated. The linear interrelations of the dissipation energy coefficients and the yield strength and peak strength were explored. The method was proposed to determine the strength of rock using the dissipation energy coefficients. The results show that the evolution of the dissipation energy coefficient exhibits significant deformation properties of rock. The dissipation energy coefficients linearly increase with the compaction strength, but decrease with the yield strength and peak strength. Moreover, the dissipation energy coefficient can be used to determine the rock burst proneness and crack propagation in rocks.

Study on Damage of Rock Samples with Single-Hole under Uniaxial Compression Condition

2012 ◽  
Vol 446-449 ◽  
pp. 3810-3813
Author(s):  
Bing Xie ◽  
Huai Feng Tong ◽  
Xiang Xia
Keyword(s):  
Compressive Strength ◽  
Uniaxial Compression ◽  
Uniaxial Compressive Strength ◽  
Particle Flow ◽  
Particle Flow Code ◽  
Compression Tests ◽  
Rock Samples ◽  
Single Hole ◽  
Compression Condition

Numerical specimens with single-hole is established by particle flow code PFC2D and uniaxial compression tests are conducted. Studies have shown that uniaxial compressive strength of specimen with single hole is less than complete specimens. As the holes move to the end of specimen, the uniaxial compressive strength first increases and then tends to decrease.

scholarly journals Effect of High Temperature and Inclination Angle on Mechanical Properties and Fracture Behavior of Granite at Low Strain Rate

2020 ◽  
Vol 12 (3) ◽  
pp. 1255 ◽  
Author(s):  
Liang Chen ◽  
Xianbiao Mao ◽  
Peng Wu
Keyword(s):  
Mechanical Properties ◽  
Shear Stress ◽  
Elastic Modulus ◽  
Crack Initiation ◽  
Uniaxial Compression ◽  
Inclination Angle ◽  
Shear Failure ◽  
Nuclear Waste Repository ◽  
Compression Stress ◽  
Peak Compression

Comprehensive understanding of the effects of temperature and inclination angle on mechanical properties and fracture modes of rock is essential for the design of rock engineering under complex loads, such as the construction of nuclear waste repository, geothermal energy development and stability assessment of deep pillar. In this paper, a novel inclined uniaxial compression (inclined UCS) test system was introduced to carry out two series of inclined uniaxial compression tests on granite specimens under various inclination angles (0–20°) and treated temperatures (25–800 °C) at 5° inclination. Experimental results revealed that the peak compression stress and elastic modulus gradually decreased, while peak shear stress increased nonlinearly with the increasing inclination angle; the peak compression and shear stress as well as elastic modulus slightly increased from 25 to 200 °C, then gradually decreased onwards with the increasing temperature. The effect of temperature on peak axial strain was the same as that on peak shear displacement. Acoustic emission (AE) results suggested that the relationship between crack initiation stress, inclination angle and treated temperature followed a similar trend as that of the peak compression stress and elastic modulus. Particularly, the crack initiation (CI) stress threshold and shear stress corresponding to CI threshold under 800 °C were only 7.4% of that under 200 °C and revealed a severe heat damage phenomenon, which was consistent with the results of the scanning electron microscopy (SEM) with the appearance of a large number of thermal pores observed only under 800 °C. The failure modes tended to shear failure with the increasing inclination angle, indicating that the shear stress component can accelerate sliding instability of rocks. On the other hand, the failure patterns with different temperatures changed from combined splitting-shear failure (25–400 °C) to single shear failure (600 and 800 °C). The study results can provide an extremely important reference for underground thermal engineering construction under complex loading environment.

scholarly journals Numerical Investigation of Mineral Grain Shape Effects on Strength and Fracture Behaviors of Rock Material

2019 ◽  
Vol 9 (14) ◽  
pp. 2855 ◽  
Author(s):  
Zhenhua Han ◽  
Luqing Zhang ◽  
Jian Zhou
Keyword(s):  
Elastic Modulus ◽  
Quantitative Methods ◽  
Significant Positive Correlation ◽  
Grain Shape ◽  
Peak Strength ◽  
Particle Flow ◽  
Particle Flow Code ◽  
Mechanical Behaviors ◽  
Fracture Behaviors ◽  
Shape Effects

Rock is an aggregate of mineral grains, and the grain shape has an obvious influence on rock mechanical behaviors. Current research on grain shape mostly focuses on loose granular materials and lacks standardized quantitative methods. Based on the CLUMP method in the two-dimensional particle flow code (PFC2D), three different grain groups were generated: strip, triangle, and square. Flatness and roughness were adopted to describe the overall contour and the surface morphology of the mineral grains, respectively. Simulated results showed that the grain shape significantly affected rock porosity and further influenced the peak strength and elastic modulus. The peak strength and elastic modulus of the model with strip-shaped grains were the highest, followed by the models with triangular and square grains. The effects of flatness and roughness on rock peak strength were the opposite, and the peak strength had a significant, positive correlation with cohesion. Tensile cracking was dominant among the generated microcracks, and the percentage of tensile cracking was maximal in the model with square grains. At the postpeak stage, the interlocking between grains was enhanced along with the increased surface roughness, which led to a slower stress drop.

scholarly journals Fracture Failure Characteristics of Jointed Sandstone under Uniaxial Compression

Geofluids ◽  
2020 ◽  
Vol 2020 ◽  
pp. 1-14
Author(s):  
Ronghua Su ◽  
Xiaolin Liu
Keyword(s):  
Uniaxial Compression ◽  
Underground Mining ◽  
Fractal Theory ◽  
Dynamic Strain ◽  
Compression Tests ◽  
Failure Characteristics ◽  
Starting Position ◽  
Fracture Failure ◽  
Fracture Evolution ◽  
Coupled Heat And Moisture

Jointed rocks are ubiquitous in the complex environments (coupled heat and moisture conditions) encountered in deep underground mining. To investigate the influence of the joint locations on the strength, deformation, and fracture failure characteristics of the jointed sandstone, uniaxial compression tests were carried out for sandstone specimens in a natural moisture state and with a preexisting joint in different locations. The entire test process was recorded by a dynamic strain acquisition system and digital speckle observation equipment. The results show that the peak strength weakening of the jointed sandstone was different with different joint positions. The residual strength and lateral deformation of the jointed sandstone were affected by the location of the joint. The joint locations dominated the evolution of the fractures in the sandstone and influenced the failure mode. The fracture evolution in sandstone with a joint in the middle was characterized by the closure of the fractures away from the starting position and was finally destroyed by the combination of shearing and splitting. The evolution of fractures in the sandstone with a joint at the bottom was stopped on the other side, which was eventually sheared across the joint. Besides, based on fractal theory, the fracture distribution on the specimen surface was analysed at certain points (first appearance of fracture, peak point) and the final destruction state during the fracture evolution. The fractal dimension was obtained, which further characterizes the fracture evolution and failure of sandstone with a joint at different locations.

scholarly journals Uniaxial Experimental Study of the Deformation Behavior and Energy Evolution of Conjugate Jointed Rock Based on AE and DIC Methods

2020 ◽  
Vol 2020 ◽  
pp. 1-16
Author(s):  
Jiliang Pan ◽  
Xu Wu ◽  
Qifeng Guo ◽  
Xun Xi ◽  
Meifeng Cai
Keyword(s):  
Stress Field ◽  
Uniaxial Compression ◽  
Testing Machine ◽  
Peak Strength ◽  
Image Correlation ◽  
Compression Tests ◽  
Dissipation Energy ◽  
Included Angle ◽  
Natural Rock ◽  
Ae Counts

Conjugate joint is one of the most common joint forms in natural rock mass, which is produced by different tectonic movements. To better understand the preexisting flaws, it is necessary to investigate joint development and its effect on the deformation and strength of the rock. In this study, uniaxial compression tests of granite specimens with different conjugate joints distribution were performed using the GAW-2000 compression-testing machine system. The PCI-2 acoustic emission (AE) testing system was used to monitor the acoustic signal characteristics of the jointed specimens during the entire loading process. At the same time, a 3D digital image correlation (DIC) technique was used to study the evolution of stress field before the peak strength at different loading times. Based on the experimental results, the deformation and strength characteristics, AE parameters, damage evolution processes, and energy accumulation and dissipation properties of the conjugate jointed specimens were analyzed. It is considered that these changes were closely related to the angle between the primary and secondary joints. The results show that the AE counts can be used to characterize the damage and failure of the specimen during uniaxial compression. The local stress field evolution process obtained by the DIC can be used to analyze the crack initiation and propagation in the specimen. As the included angle increases from 0° to 90°, the elastic modulus first decreases and then increases, and the accumulative AE counts of the peak first increase and then decrease, while the peak strength does not change distinctly. The cumulative AE counts of the specimen with an included angle of 45° rise in a ladder-like manner, and the granite retains a certain degree of brittle failure characteristics under the axial loading. The total energy, elastic energy, and dissipation energy of the jointed specimens under uniaxial compression failure were significantly reduced. These findings can be regarded as a reference for future studies on the failure mechanism of granite with conjugate joints.

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