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

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.

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

10.21203/rs.3.rs-422917/v1 ◽

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.

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

Shock and Vibration ◽

10.1155/2020/8865958 ◽

2020 ◽

Vol 2020 ◽

pp. 1-13 ◽

Cited By ~ 2

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.

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

Scientific Reports ◽

10.1038/s41598-020-74556-1 ◽

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.

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Investigation of Microcrack Propagation and Energy Evolution in Brittle Rocks Based on the Voronoi Model

Materials ◽

10.3390/ma14092108 ◽

2021 ◽

Vol 14 (9) ◽

pp. 2108

Author(s):

Guanlin Liu ◽

Youliang Chen ◽

Xi Du ◽

Peng Xiao ◽

Shaoming Liao ◽

...

Keyword(s):

Uniaxial Compression ◽

Damage Evolution ◽

Rock Sample ◽

Rock Fracture ◽

Damage Threshold ◽

Crack Development ◽

Energy Evolution ◽

Shear Cracks ◽

Compression Tests ◽

Microcrack Propagation

The cracking of rock mass under compression is the main factor causing structural failure. Therefore, it is very crucial to establish a rock damage evolution model to investigate the crack development process and reveal the failure and instability mechanism of rock under load. In this study, four different strength types of rock samples from hard to weak were selected, and the Voronoi method was used to perform and analyze uniaxial compression tests and the fracture process. The change characteristics of the number, angle, and length of cracks in the process of rock failure and instability were obtained. Three laws of crack development, damage evolution, and energy evolution were analyzed. The main conclusions are as follows. (1) The rock’s initial damage is mainly caused by tensile cracks, and the rapid growth of shear cracks after exceeding the damage threshold indicates that the rock is about to be a failure. The development of micro-cracks is mainly concentrated on the diagonal of the rock sample and gradually expands to the middle along the two ends of the diagonal. (2) The identification point of failure precursor information in Acoustic Emission (AE) can effectively provide a safety warning for the development of rock fracture. (3) The uniaxial compression damage constitutive equation of the rock sample with the crack length as the parameter is established, which can better reflect the damage evolution characteristics of the rock sample. (4) Tensile crack requires low energy consumption and energy dispersion is not concentrated. The damage is not apparent. Shear cracks are concentrated and consume a large amount of energy, resulting in strong damage and making it easy to form macro-cracks.

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The Effect of Bedding Structure on Mechanical Property of Coal

Advances in Materials Science and Engineering ◽

10.1155/2014/952703 ◽

2014 ◽

Vol 2014 ◽

pp. 1-7 ◽

Cited By ~ 5

Author(s):

Zetian Zhang ◽

Ru Zhang ◽

Guo Li ◽

Hegui Li ◽

Jianfeng Liu

Keyword(s):

Mechanical Property ◽

Uniaxial Compression ◽

Peak Stress ◽

Natural Fracture ◽

Test Results ◽

Compression Tests ◽

Average Amount ◽

Uniaxial Compression Strength ◽

Bedding Planes ◽

Close Relationship

The mechanical property of coal, influencing mining activity considerably, is significantly determined by the natural fracture distributed within coal mass. In order to study the effecting mechanism of bedding structure on mechanical property of coal, a series of uniaxial compression tests and mesoscopic tests have been conducted. The experimental results show that the distribution characteristic of calcite particles, which significantly influences the growth of cracks and the macroscopic mechanical properties of coal, is obviously affected by the bedding structure. Specifically, the uniaxial compression strength of coal sample is mainly controlled by bedding structure, and the average peak stress of specimens with axes perpendicular to the bedding planes is 20.00 MPa, which is 2.88 times the average amount of parallel ones. The test results also show a close relationship between the bedding structure and the whole deformation process under uniaxial loading.

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

Advanced Materials Research ◽

10.4028/www.scientific.net/amr.446-449.3810 ◽

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.

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Characteristic strength and acoustic emission properties of weakly cemented sandstone at different depths under uniaxial compression

International Journal of Coal Science & Technology ◽

10.1007/s40789-021-00462-0 ◽

2021 ◽

Author(s):

Bin Liu ◽

Yixin Zhao ◽

Cun Zhang ◽

Jinlong Zhou ◽

Yutao Li ◽

...

Keyword(s):

Acoustic Emission ◽

Uniaxial Compression ◽

Failure Modes ◽

Shear Failure ◽

Underground Mining ◽

Peak Strength ◽

Dissipated Energy ◽

Burial Depth ◽

Characteristic Strength ◽

Different Depths

AbstractAs coal mining is extended from shallow to deep areas along the western coalfield, it is of great significance to study weakly cemented sandstone at different depths for underground mining engineering. Sandstones from depths of 101.5, 203.2, 317.3, 406.9, 509.9 and 589.8 m at the Buertai Coal Mine were collected. The characteristic strength, acoustic emission (AE), and energy evolution of sandstone during uniaxial compression tests were analyzed. The results show that the intermediate frequency (125–275 kHz) of shallow rock mainly occurs in the postpeak stage, while deep rock occurs in the prepeak stage. The initiation strength and damage strength of the sandstone at different depths range from 0.23 to 0.50 and 0.63 to 0.84 of peak strength (σc), respectively, decrease exponentially and are a power function with depth. The precursor strength ranges from 0.88σc to 0.99σc, increases with depth before reaching a depth of 300 m, and tends to stabilize after 300 m. The ratio of the initiation strength to the damage strength (k) ranges from 0.25 to 0.62 and decreases exponentially with depth. The failure modes of sandstone at different depths are tension-dominated mixed tensile-shear failure. Shear failure mainly occurs at the unstable crack propagation stage. The count of the shear failure bands before the peak strength increases gradually, and increases first and then decreases after the peak strength with burial depth. The cumulative input energy, released elastic energy and dissipated energy increase with depth. The elastic release rate ranges from 0.46 × 10–3 to 198.57 × 10–3 J/(cm3 s) and increases exponentially with depth.

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

Applied Sciences ◽

10.3390/app9142855 ◽

2019 ◽

Vol 9 (14) ◽

pp. 2855 ◽

Cited By ~ 4

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.

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Nonlinear Dynamic Constitutive Model of Frozen Sandstone Based on Weibull Distribution

Advances in Civil Engineering ◽

10.1155/2020/6439207 ◽

2020 ◽

Vol 2020 ◽

pp. 1-10 ◽

Cited By ~ 1

Author(s):

Lei Wang ◽

Hongming Su ◽

Shiguan Chen ◽

Yue Qin

Keyword(s):

Elastic Modulus ◽

Constitutive Model ◽

Strain Rate ◽

Split Hopkinson Pressure Bar ◽

Soft Rock ◽

Strain Curve ◽

Peak Stress ◽

Experimental Results ◽

Compression Tests ◽

Hopkinson Pressure Bar

To obtain the dynamic mechanical properties of frozen sandstone at different temperatures (i.e., 20°C, −10°C, −20°C, and −30°C), dynamic uniaxial compression tests of saturated sandstone are conducted using a split-Hopkinson pressure bar. The experimental results demonstrated that the brittleness of the saturated sandstone increased and its plasticity weakened with a decrease in temperature. The peak strength and dynamic elastic modulus of the sandstone were positively correlated with its strain rate. The peak stress was most sensitive to the strain rate at −10°C, and the elastic modulus was most sensitive to the strain rate at −30°C. According to the evident segmentation characteristics of the obtained stress-strain curve, a viscoelastic dynamic constitutive model considering the strain rate effect and temperature effect is developed; this model combines a nonlinear (or linear) body and a Maxwell body in parallel with a damage body. The applicability of the constitutive model is also verified using experimental data. The fitting results were demonstrated to be in good agreement with the experimental results. Furthermore, the fitting results serve as reference for the study of the constitutive model of weakly cemented soft rock and the construction of roadway freezing methods.

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

Advances in Civil Engineering ◽

10.1155/2020/8850250 ◽

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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