scholarly journals Influence of Confining Pressure Unloading Rate on the Strength Characteristics and Fracture Process of Granite Using Lab Tests

2021 ◽  
Vol 2021 ◽  
pp. 1-16
Author(s):  
Jiaqi Guo ◽  
Pengfei Liu ◽  
Junqi Fan ◽  
Xiaoyan Shi ◽  
Xin Huang
Keyword(s):  
Acoustic Emission ◽  
Internal Friction ◽  
Strain Rate ◽  
Fracture Process ◽  
Axial Strain ◽  
Friction Angle ◽  
Confining Pressure ◽  
Tensile Fracture ◽  
Fracture Characteristics ◽  
Unloading Rate

In order to study the mechanical behaviors and fracture process properties of granite under confining pressure unloading with constant axial pressure, RMT-150B rock mechanics test system and acoustic emission detector were used to study the mechanical properties and fracture process characteristics of deeply buried granite specimens under different combinations of initial confining pressures and unloading rates. The results show that when the unloading rate is small, the deviatoric stress-strain curve of granite specimens will yield an unloading platform, and the specimens show significant characteristics of ductility; when the unloading rate is large, the specimens show characteristics of brittleness. Besides, the axial strain rate increases with the increase of initial confining pressure and unloading rate, and the axial strain rate fluctuates. The ratio of axial strain increment to confining pressure increment of granite specimens decreases with the increase of the unloading rate, and a faster unloading rate and a higher initial confining pressure will restrain the axial deformation of granite sample. The normalized confining pressure decreased parameter of granite specimen increases with the increase of initial confining pressure. When the unloading rate is relatively high, it plays a dominant role in the compressive strength of granite specimens. The Mohr–Coulomb strength criterion can better reflect the strength characteristics of specimens under confining pressure unloading. The cohesion of granite specimens decreases with the increase of unloading rate, and the internal friction angle increases with the increase of unloading rate. Notably, the unloading rate presents a weakening effect on the cohesion of the specimen and a strengthening effect on the internal friction angle of the specimen, and the former effect is stronger than the latter one. When the unloading rate is small, the acoustic emission ringing count increases more evenly, and the deformation and damage of the specimen develop slowly; when the unloading rate is high, the acoustic emission ringing count increases to the maximum instantaneously at the initial stage of confining pressure unloading, and the specimen is damaged rapidly, showing the characteristic of sudden fracture. The fracture mode of granite specimens is affected by the unloading rate and initial confining pressure. At the same unloading rate, the specimens with high initial confining pressure show typical tensile fracture characteristics, while the specimens with low initial confining pressure mainly suffer from shear fracture or shear-tension composite fracture. With the increase of unloading rate, the fracture characteristics of specimens show a transition from shear or shear-tension composite fracture to tensile fracture.

scholarly journals Mechanical Characteristics of Coal Samples under Triaxial Unloading Pressure with Different Test Paths

2020 ◽  
Vol 2020 ◽  
pp. 1-10
Author(s):  
Yang Zhang ◽  
Yongjie Yang ◽  
Depeng Ma
Keyword(s):  
Axial Strain ◽  
Triaxial Compression ◽  
Axial Loading ◽  
Peak Stress ◽  
Friction Angle ◽  
Confining Pressure ◽  
Triaxial Tests ◽  
Compression Tests ◽  
Leading Role ◽  
Unloading Rate

In order to understand the influence of unloading path on the mechanical properties of coal, triaxial unloading confining pressure tests with different initial confining pressure and different unloading rate were carried out. The test results show that the triaxial unloading strength of coal samples under different test conditions is lower than conventional triaxial tests, but the brittleness characteristics are more obvious. This result indicates that the coal samples are easily damaged under unloading conditions. In the axial loading stage of the confinement unloading tests, the axial strain plays a leading role. However, during the confining pressure unloading stage, the circumferential deformation is large, which is the main deformation in this stage. Higher unloading rates of confining pressure are associated with shorter times between the peak stress position and sample complete failure. This shows that samples are more easily destroyed under higher unloading rates and the samples are more difficultly destroyed under lower unloading rates. In addition, with increasing unloading rate, the peak principal stress difference and confining pressure at failure decrease gradually, whereas the confining pressure difference at failure increases gradually. Compared with conventional triaxial compression tests, the cohesion of coal is reduced and the internal friction angle is increased under the condition of triaxial unloading test.

Strength and Deformation Characteristics of Stabilized Silty Soil

2012 ◽  
Vol 594-597 ◽  
pp. 512-515
Author(s):  
Zheng Rong Zhao ◽  
Hong Xia Yang
Keyword(s):  
Internal Friction ◽  
Brittle Failure ◽  
Yellow River ◽  
Strain Curve ◽  
Friction Angle ◽  
Confining Pressure ◽  
Alluvial Plain ◽  
The Yellow River ◽  
Stress Strain Curve ◽  
Silty Soil

Combined with the silty soil characteristics of the Yellow River alluvial plain and the subgrade filling of Ji-He expressway, the paper discusses silty soil, stabilized silty soil strength and stress-stain characteristics through the indoor triaxial shear test. The results show that the remodeling silty soil has obvious peak, brittle failure, low residual strength after being destroyed and the stress-strain curve shows a softening type in confining pressure 100kPa lower stress level. In the confining pressure 400kPa higher stress level, soil samples peak is not obvious,mainly plastic failure and the stress-strain curve is close to a hardening type. Compared to mixed with 8% lime, stabilized silty soil of mixed with 4% cement and 4% lime shows that the partial stress peak is more obvious when destroyed and the residual strength is drastically reduced and more incline to brittle failure. In different the age, compared to mixed with 8% lime, stabilized silty soil of mixed with 4% cement and 4% lime shows that internal friction angle becomes larger and cohesion improves gradually whose amplitude is much larger than internal friction angle. Therefore, a more effective way to stabilize the silty soil of the Yellow River alluvial plain is to select silty soil mixed with 4% cement and 4% lime.

scholarly journals Three-Dimensional Combined Finite-Discrete Element Modeling of Shear Fracture Process in Direct Shearing of Rough Concrete–Rock Joints

2020 ◽  
Vol 10 (22) ◽  
pp. 8033
Author(s):  
Gyeongjo Min ◽  
Daisuke Fukuda ◽  
Sewook Oh ◽  
Gyeonggyu Kim ◽  
Younghun Ko ◽  
...  
Keyword(s):  
Friction Coefficient ◽  
Internal Friction ◽  
Fracture Process ◽  
Three Dimensional ◽  
Friction Angle ◽  
Discrete Element ◽  
Shear Resistance ◽  
Internal Friction Angle ◽  
Rock Joints ◽  
Joint Shear

A three-dimensional combined finite-discrete element element method (FDEM), parallelized by a general-purpose graphic-processing-unit (GPGPU), was applied to identify the fracture process of rough concrete–rock joints under direct shearing. The development process of shear resistance under the complex interaction between the rough concrete–rock joint surfaces, i.e., asperity dilatation, sliding, and degradation, was numerically simulated in terms of various asperity roughness under constant normal confinement. It was found that joint roughness significantly affects the development of overall joint shear resistance. The main mechanism for the joint shear resistance was identified as asperity sliding in the case of smoother joint roughness and asperity degradation in the case of rougher joint asperity. Moreover, it was established that the bulk internal friction angle increased with asperity angle increments in the Mohr–Coulomb criterion, and these results follow Patton’s theoretical model. Finally, the friction coefficient in FDEM appears to be an important parameter for simulating the direct shear test because the friction coefficient affects the bulk shear strength as well as the bulk internal friction angle. In addition, the friction coefficient of the rock–concrete joints contributes to the variation of the internal friction angle at the smooth joint than the rough joint.

scholarly journals Acoustic Emission Simulation on Coal Specimen Subjected to Cyclic Loading

2020 ◽  
Vol 2020 ◽  
pp. 1-17
Author(s):  
Huiqiang Duan ◽  
Depeng Ma
Keyword(s):  
Numerical Simulation ◽  
Acoustic Emission ◽  
Cyclic Loading ◽  
Confining Pressure ◽  
Rock Masses ◽  
Coal Specimen ◽  
Cycle Number ◽  
Confining Pressures ◽  
Unloading Rate ◽  
Ae Counts

The damage and failure state of the loaded coal and rock masses is indirectly reflected by its acoustic emission (AE) characteristics. Therefore, it is of great significance to study the AE evolution of loaded coal and rock masses for the evaluation of damage degree and prediction of collapse. The paper mainly represents a numerical simulation investigation of the AE characteristics of coal specimen subjected to cyclic loading under three confining pressures, loading-unloading rates, and valley stresses. From the numerical simulation tests, the following conclusions can be drawn: (1) The final cycle number of coal specimen subjected to cyclic loading is significantly influenced by the confining pressure, followed the valley stress. With the increase in confining pressure or valley stress, the cycle number tends to increase. However, the loading-unloading rate has a little influence on it. (2) The AE counts of coal specimen subjected to cyclic loading are greatly influenced by the confining pressure and the valley stress. With the increase in the confining pressure, the cumulative AE counts at the 1st cycle tend to increase but decrease at a cycle before failure; with the decrease in the valley stress, the cumulative AE counts per cycle increase in the relatively quiet phase. However, the loading-unloading rate has a little influence on it. (3) The failure mode of coal specimen subjected to cyclic loading is significantly influenced by the confining pressure. Under the uniaxial stress state, there is an inclined main fractured plane in the coal specimen, under the confining pressures of 5 and 10 MPa, the coal specimen represents dispersion failure. The loading-unloading rate and valley stress have little influence on it. (4) The AE ratio is proposed, and its evolution can better reflect the different stages of coal specimen failure under cyclic loading. (5) The influence of confining pressure on the broken degree of coal specimen subjected to cyclic loading is analyzed, and the higher the confining pressure, the more broken the failed coal specimen.

Experimental Study of Rockfill Particle Breakage

2014 ◽  
Vol 900 ◽  
pp. 445-448
Author(s):  
Zhi Hua Xu ◽  
Da Wei Sun
Keyword(s):  
Internal Friction ◽  
Large Scale ◽  
Reference Value ◽  
Friction Angle ◽  
Confining Pressure ◽  
Particle Breakage ◽  
Internal Friction Angle ◽  
Dam Construction ◽  
Confining Pressures ◽  
The Relationship

As the high concrete faced rockfill dams construction, grain breakage gradually become the factors that influence the high dam construction which can not be ignored. This text based on the master of rockfill of shuibuya dam as the experimental material, getting and analyzing the particle breakage data under different confining pressure through the large-scale triaxial test, and the results show that the particle breakage index increases with the increase of confining pressures. The relationship between particle breakage index and confining pressure can be expressed by formula;Particle breakage increase leading to reduced internal friction angle and the shear strength of rockfill, and the author newly introduced two broken variable to describe the relationship which can be expressed by the formula between the particle breakage and internal friction angle, it has certain reference value for establishing constitutive model considering particle breakage.

Small-strain behavior of frozen sand in triaxial compression

1995 ◽  
Vol 32 (3) ◽  
pp. 428-451 ◽  
Author(s):  
Glen R. Andersen ◽  
Christopher W. Swan ◽  
Charles C. Ladd ◽  
John T. Germaine
Keyword(s):  
High Pressure ◽  
Strain Rate ◽  
Yield Stress ◽  
Axial Strain ◽  
Triaxial Compression ◽  
Strain Curve ◽  
Confining Pressure ◽  
Stress Strain ◽  
Strain Behavior ◽  
Frozen Sand

The stress–strain behavior of frozen Manchester fine sand has been measured in a high-pressure low-temperature triaxial compression testing system developed for this purpose. This system incorporates DC servomotor technology, lubricated end platens, and on-specimen axial strain devices. A parametric study has investigated the effects of changes in strain rate, confining pressure, sand density, and temperature on behavior for very small strains (0.001%) to very large (> 20%) axial strains. This paper presents constitutive behavior for strain levels up to 1%. On-specimen axial strain measurements enabled the identification of a distinct upper yield stress (knee on the stress–strain curve) and a study of the behavior in this region with a degree of precision not previously reported in the literature. The Young's modulus is independent of strain rate and temperature, increases slightly with sand density in a manner consistent with Counto's model for composite materials, and decreases slightly with confining pressure. In contrast, the upper yield stress is independent of sand density, slightly dependent on confining pressure (considered a second order effect), but is strongly dependent on strain rate and temperature in a fashion similar to that for polycrystalline ice. Key words : frozen sand, high-pressure triaxial compression, strain rate, temperature, modulus, yield stress.

Acoustic Emission Characteristics of Sericite Schist Coarse Aggregates under Consolidated Undrained Triaxial Tests

2013 ◽  
Vol 423-426 ◽  
pp. 909-913
Author(s):  
Lan Qiang Yang ◽  
Shang Lin Qin ◽  
Hui Gao ◽  
Shan Xiong Chen
Keyword(s):  
Acoustic Emission ◽  
Large Scale ◽  
Sliding Friction ◽  
Axial Strain ◽  
Confining Pressure ◽  
Rolling Friction ◽  
Triaxial Tests ◽  
Emission Characteristics ◽  
Coarse Aggregates ◽  
Ae Signals

In order to study the acoustic emission characteristics of coarse aggregates, improved of large-scale triaxial apparatus is used to do the consolidated undrained triaxial tests of sericite schist coarse aggregates, with the acoustic emission signals monitoring. The test results show that a large number of AE signals of sericite schist coarse aggregates are generated in the initial stage. Before the axial strain reach 10%, AE counts are relatively quiet. But after 10%, they become anomalous and emerge obvious leap values. When the confining pressure up to 200kPa, AE signals are mainly generated by sliding friction. With confining pressure increasing, the proporation of rolling friction and particle breakage is more and more obvious.

Gravel Content Effect on the Shear Strength of Clay-Gravel Mixtures

2011 ◽  
Vol 71-78 ◽  
pp. 4685-4688 ◽  
Author(s):  
Chen Wang ◽  
Chuan Ni Zhan
Keyword(s):  
Shear Strength ◽  
Internal Friction ◽  
Triaxial Compression ◽  
Constant Strain Rate ◽  
Friction Angle ◽  
Confining Pressure ◽  
Internal Friction Angle ◽  
Compression Tests ◽  
Gravel Content ◽  
Confining Pressures

Gravel content is an important factor affecting the mechanical properties of clay-gravel mixtures. To study the effects of gravel content on the shear strength of clay-gravel mixtures, constant-strain-rate drained triaxial compression tests were conducted for various mixtures. The gravel contents were 30%, 40%, 50% and 70%. The confining pressures were varied from 50kPa to 300kPa. Test results indicate that the deviator stress at failure under the same confining pressure increases with the increase in gravel content. As the gravel content in the mixtures is between 30% and 50%, the shear strength is jointly attributed by clay and gravel. An increase in gravel content results in slight increases in both the cohesion intercept and internal friction angle. At gravel content of up to 70%, the shear strength of the mixture is controlled by that of the gravel, and the cohesion intercept and the internal friction angle increase sharply.

scholarly journals Physical and Mechanical Properties of Gypsum-Like Rock Materials

2020 ◽  
Vol 2020 ◽  
pp. 1-17 ◽  
Author(s):  
Sijiang Wei ◽  
Chongyang Wang ◽  
Yushun Yang ◽  
Meng Wang
Keyword(s):  
High Temperature ◽  
Internal Friction ◽  
Triaxial Compression ◽  
Physical And Mechanical Properties ◽  
High Strength ◽  
Friction Angle ◽  
Confining Pressure ◽  
Peak Intensity ◽  
Saturated Sample ◽  
Gypsum Rock

In the process of tunnel construction, gypsum rock is often encountered, and the volume of gypsum rock expands when encountering water, which is easy to cause the occurrence of rock fall, collapse, and other disasters, bringing serious challenges to the safe construction of the tunnel. Therefore, in this paper, four groups of samples under different moisture content are tested by ultrasonography, uniaxial compression, conventional triaxial compression, Brazilian splitting, X-ray diffraction, and SEM, and then the physical and mechanical properties of gypsum rock are studied, and the conclusion is as follows: the density of the water saturated sample, and the longitudinal wave velocity of the natural sample are the highest. Both the water saturation and dehydration conditions have a weakening effect on the remolded sample of high-strength gypsum powder. The peak intensity of the sample gradually increases with the increase of confining pressure, and the relationship between the peak intensity and confining pressure of the sample conforms to the Coulomb strength criterion. After high-temperature dehydration, the sample showed obvious plastic softening characteristics. The cohesion and internal friction angle of the sample are closely related to the water content. The cohesion is the largest in the 45°C dehydrated sample, the internal friction angle is the smallest in the saturated sample, whereas the cohesion is the smallest and internal friction is the largest in the high-temperature dehydrated sample. The characteristics of failure for the natural and 45°C dehydrated samples are almost the same and most samples show shear or shear-tensile failure. The shear plane begins at the edge of the end face of the sample and exhibits a typical diagonal shear failure. The high-temperature dehydrated samples are completely broken under uniaxial and triaxial compression conditions. After high-strength gypsum powder was used to make the remolded sample, the calcium sulfate disappeared, the water content increased, and the main mineral components of the natural and saturated samples were the same. After dehydration at 45°C, the sample began to release structural water and generate SiO2. After high-temperature dehydration, the hemihydrate gypsum continued to dehydrate and become soluble anhydrous gypsum.

scholarly journals Experimental Study on Mechanical Properties and Seepage Laws of Raw Coal under Variable Loading and Unloading Rates

Geofluids ◽  
2021 ◽  
Vol 2021 ◽  
pp. 1-9
Author(s):  
Kangwu Feng ◽  
Kequan Wang ◽  
Dongming Zhang ◽  
Yushun Yang
Keyword(s):  
Axial Stress ◽  
Axial Strain ◽  
Radial Strain ◽  
High Sensitivity ◽  
Confining Pressure ◽  
Variable Loading ◽  
Axial Pressure ◽  
Unloading Rate ◽  
Loading And Unloading ◽  
Seepage Characteristics

This manuscript studied the effects of variable axial pressure loading rate and variable confining pressure unloading rate on the deformation behavior and seepage characteristics of raw coal under alternate loading and unloading of axial pressure and confining pressure. It believed that as axial stress increases, axial strain ε 1 decreases, radial strain ε 3 increases, and permeability k decreases, and ε 1 ′ , ε 3 ′ , and k ′ increase when confining pressure is decreases. With the loading of axial stress and the unloading of confining pressure, the variation amplitudes of ε 1 ′ , ε 3 ′ , and k ′ values reduce gradually. During axial stress loading, the rise in the amplitude of ε 1 is larger than that of ε 3 and the reduction in the amplitude of k , indicating that ε 1 is more sensitive to axial stress than ε 3 and k . During unloading of confining pressure, the increase rate of ε 3 is larger than that of ε 1 and k ; also, ε 3 showed a high sensitivity to confining pressure. In the stage of axial stress loading and confining pressure unloading, the evolution law of deformation and permeability parameters is basically consistent with the change in loading and unloading rate.

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