scholarly journals Mechanical Properties and Failure Modes of Thick-Walled Cylinder Granites with Different Apertures under Triaxial Compression

2020 ◽  
Vol 2020 ◽  
pp. 1-18
Author(s):  
Wei Chen ◽  
Wen Wan ◽  
Shuailong Lian ◽  
Senlin Xie ◽  
Yu Zhou ◽  
...  
Keyword(s):  
Failure Modes ◽  
Shear Failure ◽  
Triaxial Compression ◽  
Confining Pressure ◽  
Outer Wall ◽  
Surrounding Rock ◽  
Compression Tests ◽  
Deformation And Failure ◽  
Triaxial Compressive Strength ◽  
Walled Cylinder

Roadway excavation changes the original equilibrium stress state of the rock mass, resulting in the loading and unloading of the surrounding rock near the free surface. After the excavation, the tangential stress increases and the radial stress decreases, which mainly cause deformation and collapse of the roadway. In order to study the strength characteristics of the surrounding rock after the excavation, one effective way is to carry out triaxial compression tests on small surrounding rock samples. Therefore, this paper focuses on the triaxial compression mechanical propertiesof thick-walled cylinder granites with an electrohydraulic, servo-controlled rock mechanics testing system (MTS-815). It studies how different pore sizes and confining pressures affect the triaxial compressive strength (TCS), deformation, and failure modes of granite samples. The results are as follows: (1) Under triaxial compression, the stress-strain curves have no obvious yield stage, and the peak TCS increases with the confining pressure (σ3). When σ3 is low, there is little difference in the TCS between the complete specimen and the thick-walled cylinders. When σ3 reaches 30 MPa∼40 MPa, the TCS of samples with apertures of 15 mm and 20 mm are obviously lower. The σ3 has an obvious influence on the elastic modulus of thick-walled cylinder granites. (2) Shearing and splitting are the main failure modes under triaxial compression. When σ3 is low, shear failure appears. As σ3 reaches 30 MPa∼40 MPa, split failure occurs. The area of the fracture surface increases with σ3. (3) As σ3 grows, the influence parameter (m) of the three-dimensional Hoek-Brown criterion increases. Under the same σ3, the value of m presents a decreasing trend from the outer wall to the inner wall, which means the bearing capacity keeps getting lower and lower. As a result, the inner wall is most likely to be damaged. The theoretical analysis results agree well with the tests.

scholarly journals Experimental Investigation on Failure Modes and Mechanical Properties of Rock-Like Specimens with a Grout-Infilled Flaw under Triaxial Compression

2019 ◽  
Vol 2019 ◽  
pp. 1-14
Author(s):  
Huilin Le ◽  
Shaorui Sun ◽  
Feng Zhu ◽  
Haotian Fan
Keyword(s):  
Mechanical Properties ◽  
Rock Mass ◽  
Epoxy Resin ◽  
Failure Modes ◽  
Shear Failure ◽  
Fractured Rock ◽  
Triaxial Compression ◽  
Friction Angle ◽  
Confining Pressure ◽  
Compression Tests

Flaws existing in rock mass are one of the main factors resulting in the instability of rock mass. Epoxy resin is often used to reinforce fractured rock mass. However, few researches focused on mechanical properties of the specimens with a resin-infilled flaw under triaxial compression. Therefore, in this research, epoxy resin was selected as the grouting material, and triaxial compression tests were conducted on the rock-like specimens with a grout-infilled flaw having different geometries. This study draws some new conclusions. The high confining pressure suppresses the generation of tensile cracks, and the failure mode changes from tensile-shear failure to shear failure as the confining pressure increases. Grouting with epoxy resin leads to the improvement of peak strengths of the specimens under triaxial compression. The reinforcement effect of epoxy resin is better for the specimens having a large flaw length and those under a relatively low confining pressure. Grouting with epoxy resin reduces the internal friction angle of the samples but improves their cohesion. This research may provide some useful insights for understanding the mechanical behaviors of grouted rock masses.

scholarly journals Cracking Behaviors and Mechanical Properties of Rock-Like Specimens with Two Unparallel Flaws under Conventional Triaxial Compression

2019 ◽  
Vol 2019 ◽  
pp. 1-15 ◽  
Author(s):  
Huilin Le ◽  
Shaorui Sun ◽  
Chenghua Xu ◽  
Liuyang Li ◽  
Yong Liu
Keyword(s):  
Mechanical Properties ◽  
Inclination Angle ◽  
Failure Modes ◽  
Shear Failure ◽  
Triaxial Compression ◽  
Confining Pressure ◽  
Critical Value ◽  
Tensile Failure ◽  
Rock Bridge ◽  
Bridge Length

Flaws existing in rock masses are generally unparallel and under three-dimensional stress; however, the mechanical and cracking behaviors of the specimens with two unparallel flaws under triaxial compression have been rarely studied. Therefore, this study conducted comprehensive research on the cracking and coalescence behavior and mechanical properties of specimens with two unparallel flaws under triaxial compression. Triaxial compressive tests were conducted under different confining pressures on rock-like specimens with two preexisting flaws but varying flaw geometries (with respect to the inclination angle of the two unparallel flaws, rock bridge length, and rock bridge inclination angle). Six crack types and eleven coalescence types in the bridge region were observed, and three types of failure modes (tensile failure, shear failure, and tensile-shear failure) were observed in experiments. Test results show that bridge length and bridge inclination angle have an effect on the coalescence pattern, but the influence of bridge inclination angle is larger than that of the bridge length. When the confining pressure is low, coalescence patterns and failure modes of the specimens are greatly affected by flaw geometry, but when confining pressure rose to a certain level, the influence of confining pressure is larger than the effect of flaw geometry. The peak strength of the specimens is affected by flaw geometry and confining pressure. There is a critical value for the bridge length. If the bridge length is larger than the critical value, peak strengths of the samples almost keep constant as the bridge length increases. In addition, as the bridge inclination angle increases, there is an increase in the probability of tensile cracks occurring, and with an increase in the confining pressure, the probability of the occurrence of shear cracks increases.

Comment on “Plastic deformation and fracture behavior of a Fe-modified Al3Ti-base L12 intermetallic alloy” [J. Mater. Res. 6, 957 (1991)]: The importance of specimen length-to-width ratios and end constraints in compression testing of brittle and semibrittle materials

1992 ◽  
Vol 7 (7) ◽  
pp. 1956-1959 ◽  
Author(s):  
David H. Zeuch
Keyword(s):  
Failure Modes ◽  
Shear Failure ◽  
Compression Tests ◽  
Specimen Length ◽  
End Effects ◽  
Deformation And Failure ◽  
Test Configuration ◽  
Pressure Sensitive ◽  
End Conditions ◽  
Test Pressure

Specimen length-to-diameter ratios and specimen/platen end conditions are important to interpretation of, and comparisons between, uniaxial compression tests on brittle materials. When differing l:d ratios and specimen/platen end conditions are used to test pressure-sensitive materials, observations may not be readily comparable owing to the different and nonuniform triaxial stress states. Specimens of brittle Fe- and Ni-modified Al3Ti intermetallic alloys having relatively low and different l:d ratios were tested in compression by Gengxiang et al. and Turner et al., respectively. Qualitative observations on the macroscopic deformation and failure modes (shear failure and distributed microcracking) indicate that the alloys are pressure-sensitive and that the results were possibly complicated in differing degrees by test configuration. Thus, direct comparison of these results with those obtained earlier for Al3Ti by Yamaguchi et al., who used a significantly greater l:d ratio, may not be altogether useful. Approaches to minimizing end effects are reviewed.

scholarly journals Analysis of Failure Characteristics and Strength Criterion of Coal-Rock Combined Body with Different Height Ratios

2020 ◽  
Vol 2020 ◽  
pp. 1-14
Author(s):  
Tuo Wang ◽  
Zhanguo Ma ◽  
Peng Gong ◽  
Ning Li ◽  
Shixing Cheng
Keyword(s):  
Shear Failure ◽  
Underground Mining ◽  
Triaxial Compression ◽  
Peak Stress ◽  
Strength Criterion ◽  
Confining Pressure ◽  
Experimental Results ◽  
Compression Tests ◽  
Rock Body ◽  
Coal Rock

In underground mining and roadway support engineering of coal mine, the coal and rock layers bear loads together; therefore, the deformation and mechanical characteristics of the coal-rock combined bodies are not the same as those of the pure coal or rock bodies. In this paper, conventional triaxial compression tests of coal-rock combined bodies with different height ratios were conducted. And the stress and deformation characteristics of coal-rock combined body were studied and the experimental results were analyzed with different strength criteria. The results show that the peak stress, elastic modulus, and strength reduction coefficient of coal-rock combined body are negatively correlated with the ratio of coal to coal-rock combination height and positively correlated with the confining pressure; the coal-rock combination shows obvious ductility under 10 MPa confining pressure. Under the conventional triaxial condition, the shear failure was the main cause of the lateral deformation of the coal body in the coal-rock combination, which was much larger than that of the rock body. The circle deformation value, volume strain value, and the deformation rate in the postpeak stage of coal-rock combination are much higher than those in the prepeak stage. Mohr–Coulomb and general Hoek–Brown strength criterion fit the experimental results well.

scholarly journals Experimental Study on the Mechanical Properties and Seepage Characteristics of Red Sandstone with a Single Persistent Joint under Triaxial Compression

Geofluids ◽  
2021 ◽  
Vol 2021 ◽  
pp. 1-13
Author(s):  
Wei Wang ◽  
Shifan Liu ◽  
Chong Shi ◽  
Shanxi Zheng ◽  
Qizhi Zhu
Keyword(s):  
Mechanical Properties ◽  
Pore Pressure ◽  
Failure Modes ◽  
Shear Failure ◽  
Triaxial Compression ◽  
Confining Pressure ◽  
Strengthening Effect ◽  
Red Sandstone ◽  
Inclination Angles ◽  
Seepage Characteristics

In this research, the conventional triaxial compression experiments for intact red sandstone specimens and the specimens with a single persistent joint at different inclination angles, i.e., 0°, 30°, 45°, and 90°, were conducted at first. Based on the results of the conventional tests, the effects of the confining pressure and the joint inclination angle on the mechanical properties including deformation behavior and strength parameters were summarized and analyzed, respectively. We find that the strength and deformation of jointed red sandstone are enlarged due to the increment of confining pressure, and the mechanical parameters of specimens show a U-shaped development with the rise of the joint angle. Besides, to investigate the effects of the pore pressure on seepage characteristics of rocks with joint angles at 0°, 45°, and 90°, a series of triaxial compression drainage tests on the jointed red sandstone were performed. The results show that the pore pressure has a weakening effect on the strength of jointed specimens, which can reduce the strengthening effect induced by confining pressure. Meanwhile, the tested specimens mostly present shear failure modes. As a result, the mechanical responses, seepage characteristics, and cracking modes in red sandstone containing a single persistent joint under triaxial compression are revealed.

scholarly journals Strength and Failure Characteristics of Saturated Sandstone Under Loading and Unloading

2021 ◽  
Author(s):  
Zhenhua Zhang ◽  
Huayan Yao ◽  
Hongguo Li ◽  
Hanbin Bian ◽  
Dayong Zhu
Keyword(s):  
Failure Modes ◽  
Shear Failure ◽  
Water Saturation ◽  
Triaxial Compression ◽  
Axial Direction ◽  
Confining Pressure ◽  
Stress Path ◽  
Failure Characteristics ◽  
Dry Conditions ◽  
Unloading Confining Pressure

Abstract Water has effects on the strength and failure characteristics of the sandstone in natural environment. Conventional triaxial compressive or unloading confining pressure experiments were conducted on sandstone specimens. Experimental results indicate that the compressive strength of sandstone decreases significantly under saturated conditions in comparison with dry conditions, the strength parameters of saturated specimens under unloading confining pressure are also lower than those of dry rock samples; for the sandstone with the same water content, the strengths under triaxial unloading confining pressure is slightly higher than those under triaxial compressive condition; compared with the stress path of triaxial compression, the stress path of unloading confining pressure makes cracks propagate more easily along the axial direction, and the angle between fracture surface and axial direction is smaller. Under triaxial unloading confining pressure, there failure modes of dry sandstone are tension failure and shear failure, while that of saturated sandstone is mainly shear failure. In the process of water saturation, the bond and friction characteristics between grain particles are degraded due to water weakening the cementation between the grain particles and softening grains boundary, and the expansion of clay minerals in the sandstone, which leads to the decrease of macroscopic mechanical strengths.

scholarly journals Experimental Study on Rock-Like Specimens with Single Flaw under Hydro-Mechanical Coupling

2019 ◽  
Vol 9 (16) ◽  
pp. 3234 ◽  
Author(s):  
Jinquan Xing ◽  
Cheng Zhao ◽  
Songbo Yu ◽  
Hiroshi Matsuda ◽  
Chuangchuang Ma
Keyword(s):  
Mechanical Properties ◽  
Shear Failure ◽  
Water Pressure ◽  
Triaxial Compression ◽  
Confining Pressure ◽  
Tensile Failure ◽  
Compression Tests ◽  
Cracking Behavior ◽  
Mechanical Coupling ◽  
High Confining Pressure

In order to study the mechanical characteristics and cracking behavior of jointed rock mass under hydro-mechanical coupling, a series of uniaxial compression tests and triaxial compression tests were carried out on cylinder gypsum specimens with a single pre-existing flaw. Under different confining pressures, water pressure was injected on the pre-existing flaw surface through a water injection channel. The geometrical morphology and tensile or shear properties of the cracks were determined by X-ray computed tomography (CT) and scanning electron microscope (SEM). Based on the macro and micro observation, nine types of cracks that caused the specimen failure are summarized. The results of mechanical properties and crack behavior showed that the confining pressure inhibited the tensile cracks, and shear failure occurred under high confining pressure. The water pressure facilitated the initiation and extension of tensile crack, which made the specimens prone to tensile failure. However, under the condition of high confining pressure and low water pressure, the lubrication effect had a significant effect on the failure pattern, under which the specimens were prone to shear failure. This experimental research on mechanical properties and cracking behavior under hydro-mechanical coupling is expected to increase its fundamental understanding.

scholarly journals Experimental Investigation on the Mechanical Characteristics and Deformation Behaviour of Fractured Rock-Like Material with One Single Fissure under the Conventional Triaxial Compression

2018 ◽  
Vol 2018 ◽  
pp. 1-11 ◽  
Author(s):  
Taoli Xiao ◽  
Mei Huang ◽  
Cheng Cheng ◽  
Yunlong He
Keyword(s):  
Mechanical Characteristics ◽  
Failure Modes ◽  
Shear Failure ◽  
Early Stage ◽  
Fractured Rock ◽  
Deformation Behaviour ◽  
Triaxial Compression ◽  
Strain Curve ◽  
Confining Pressure ◽  
Material Specimen

An experimental study was carried out on a rock-like material specimen containing a single fissure to investigate its mechanical characteristics and deformation behaviour under triaxial compression. The mechanical characteristics, such as peak strength and residual strength, are discussed. The confining pressure had a distinct effect on the ductility characteristics of the specimen. “A distinct stress drop” occurred in the early stage of the stress-strain curve when the length fissure was relatively long. The I-crack, II-crack, and III-crack are all observed under triaxial compression, and the III-crack is commonly observed under triaxial compression. Confining pressure plays an essential role in affecting the failure mode of the specimen. There are three kinds of failure modes in the triaxial compression experiment on a rock-like material specimen with one single fissure: tensile-shear comprehensive failure, “X”-shaped shear failure, and shear failure along the fissure plane. These results are important and fundamental to understand the fracture mechanism of rock engineering.

Mechanical Properties of Sandstone under Loading and Unloading Conditions

2014 ◽  
Vol 852 ◽  
pp. 441-446 ◽  
Author(s):  
Xing Xia Wang ◽  
Wen Juan Ma ◽  
Jian Wen Huang ◽  
Zai Yi Liao
Keyword(s):  
Mechanical Properties ◽  
Triaxial Compression ◽  
Deformation Modulus ◽  
Confining Pressure ◽  
Rock Deformation ◽  
Test Results ◽  
Compression Tests ◽  
Triaxial Compressive Strength ◽  
Unloading Confining Pressure ◽  
Triaxial Compression Tests

The mechanical properties of rock mass under unloading conditions are essentially different from that under loading conditions. Triaxial compression tests and unloading confining pressure tests are conducted, and test results show that unloading failure is more brittle, and rock samples suffer more damage under unloading failure. The larger the initial confining pressure is, the easier of unloading failure is occurred. The increasing or decreasing values of rock deformation modulus under unloading conditions are within 10% of rock triaxial compressive strength. Unloading failure leads to deterioration of rock deformation modulus, which decreases gradually with confining pressure decreasing, and the decrease rates get bigger and bigger with unloading ratio of confining pressure increasing. Deformation modulus is only 24-34% of that under loading condition when rock strength goes down to residual strength.

scholarly journals The mechanical behaviour of rock specimens with specific edge crack distributions under triaxial loading conditions

2019 ◽  
Vol 16 (5) ◽  
pp. 962-973 ◽  
Author(s):  
Guoyong Duan ◽  
Jianlin Li ◽  
Jingyu Zhang ◽  
Zuosen Luo ◽  
Liangpeng Wan ◽  
...  
Keyword(s):  
Mechanical Behaviour ◽  
Shear Failure ◽  
Axial Stress ◽  
Triaxial Compression ◽  
Confining Pressure ◽  
Loading Conditions ◽  
Compression Tests ◽  
Joint Orientation ◽  
Failure Patterns ◽  
Rock Specimens

Abstract Research on the mechanical behaviour of rock masses with multiple joints has become a popular topic and has practical applications in natural slope stability. This paper aims to clarify the influence of joint geometry, joint orientation and joint connectivity ratio on the mechanical behaviour of rock specimens containing two pre-existing joints. Triaxial compression tests were conducted under various confining pressures to simulate the variation in external conditions. An exponential criterion was used to describe the relationship between the axial stress and confining pressure. The experimental crack propagation was explored by varying the joint orientation, joint connectivity ratio and confining pressure. The structural plane with a greater angle of inclination controlled the failure of the rock sample. Two failure patterns were observed under the loading conditions: shear failure and mixed failure. The failure surface trajectory presented similar deviations with the increase in joint inclination angle, joint connectivity ratio and confining pressure, which also accelerates the transition from mixed failure to shear failure. The experimental results highlight the significance of elucidating the influence of structural planes in practical engineering to predict the stability of natural slopes.

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