scholarly journals Deformation and Acoustic Emission Characteristics of Cracked Granite during Creep

2020 ◽  
Vol 2020 ◽  
pp. 1-11
Author(s):  
Chunping Wang ◽  
Jingli Xie ◽  
Jian Liu
Keyword(s):  
Acoustic Emission ◽  
Axial Strain ◽  
Failure Process ◽  
Deformation Characteristic ◽  
Temporal Distribution ◽  
Confining Pressure ◽  
High Energy ◽  
Lateral Strain ◽  
Creep Tests ◽  
Confining Pressures

A series of multistage creep tests under different confining pressures with acoustic emission monitoring have been performed to investigate the deformation characteristic and failure process of cracked granite during creep. The critical axial strain of cracked sample showed an increasing tendency with the increase of confining pressure. In contrast, critical lateral strain experienced a process of descending first at low confinement and then remaining nearly constant at high confinement. Compared with loading-cracked specimen, smaller critical axial strain, greater critical lateral strain, and higher lateral creep strain rate were found for unloading-cracked specimen. Based on the spatial and temporal distribution of acoustic emission events, the cracking process during creep was analysed. The AE events with high energy are mainly concentrated at the final fracture area of the specimen. The higher the confining pressure, the more the AE events with low energy. Compared with the loading-cracked specimen, the percentage of AE events with high energy is relatively small for the unloading-cracked specimen.

scholarly journals The Effect of Confining Pressure on the Mechanical Properties of Sand–Ice Materials

1973 ◽  
Vol 12 (66) ◽  
pp. 469-481 ◽  
Author(s):  
Bernard D. Alkire ◽  
Orlando B. Andersland
Keyword(s):  
Axial Strain ◽  
Triaxial Compression ◽  
Confining Pressure ◽  
Silica Sand ◽  
Creep Tests ◽  
Ice Volume ◽  
Coulomb Failure ◽  
Confining Pressures ◽  
Sand Material ◽  
Cylindrical Samples

Cylindrical samples containing 0.59 mm to 0.84 mm diameter silica sand at about 97% and 55% ice saturation (the ratio of ice volume to sand pore volume) were tested at a temperature of −12° C in triaxial compression. Both constant axial strain-rate tests and step-stress creep tests provide information on the influence of confining pressure on the shear strength and creep behavior of the sand–ice material. Changes in the degree of ice saturation help show the influence of the ice matrix versus the sand material on the mechanical behavior. Data are discussed in terms of the Mohr–Coulomb failure law and creep theories. It is shown that the cohesive component of strength depends on response of the ice matrix, whereas the frictional component of strength responds in a manner very similar to unfrozen sand tested at high confining pressures. Experimental data show that creep rates decrease exponentially and creep strength increases with an increase in confining pressure.

scholarly journals Study on Lateral Deformation and Failure Characteristics of Coal Based on Different Confining Pressures

2021 ◽  
Vol 2021 ◽  
pp. 1-11
Author(s):  
Jian-jun Ren ◽  
Shan-Yang Wei ◽  
Shi-Hai Shu ◽  
Wei-Dong Luo
Keyword(s):  
Axial Strain ◽  
Peak Stress ◽  
Confining Pressure ◽  
Lateral Strain ◽  
Lateral Deformation ◽  
Axis Ratio ◽  
Deformation And Failure ◽  
Initial Stage ◽  
Confining Pressures ◽  
Potential Parameters

To study the lateral deformation characteristics of coal under different confining pressures, coal compression experiments with confining pressures of 0 MPa, 3 MPa, 5 MPa, and 7 MPa were conducted under the same loading rate by using the TAW-2000 electrohydraulic servo rock mechanics experimental machine. The results of the study showed the following: at the initial stage of loading, the lateral strain of coal was about 12.22%–46.9% of the axial strain at the elastic deformation stage and 41.18%–64.96% of the axial strain at the inelastic deformation to peak stress stage. Compared with the experiment under 0 MPa confining pressure, the growth rate of the lateral strain of the coal under 3 MPa, 5 MPa, and 7 MPa confining pressures was much smaller than that of the corresponding axial strain. When the coal was damaged under different confining pressures, the lateral strain was maintained at about 0.6 × 10−2. Based on the field verification, we proposed that the lateral strain during the coal failure and the nonlinear region of the lateral axis ratio changing with time can be used as potential parameters for predicting the coal failure.

Strength Attenuation and Post Failure Behaviour of Fine Sandstone

2012 ◽  
Vol 446-449 ◽  
pp. 3538-3543
Author(s):  
Ji Jun Zhou ◽  
Huai Fu ◽  
Yue Zhang ◽  
Yan Li ◽  
De Zhang
Keyword(s):  
Shear Test ◽  
Fractured Rock ◽  
Axial Strain ◽  
Confining Pressure ◽  
Lateral Strain ◽  
Material Strength ◽  
Failure Behaviour ◽  
Block Shear ◽  
Stress Peak ◽  
Confining Pressures

Three types of physical tests were designed to study post failure behaviour and strength attenuation of fine sandstone. Tests include rock compression test, rock unloading test and rock block shear test. The stress-strain curves at different confining pressures had been obtained as well as axial strain-lateral strain curves. The differences of axial strain-lateral strain curves exhibit that stress peak point and the point of fault formation are apparently different for the rock. After the fault is generated, fractured rock slides on the fault surfaces, while confining pressure, material strength and structure effect decide the post failure behaviour. Damaged rock specimens were poured in concrete specimens as well as irregular blocks. Material strength of rock blocks was attained. Shear strength gradually attenuates with unloading points close to the peak. Past the stress peak, rock blocks from fractured rock still have considerable material strength. It is shown that there are differences of strength parameters obtained from direct shear test and triaxial test.

scholarly journals Experimental Investigation on the Deformation, Strength, and Acoustic Emission Characteristics of Sandstone under True Triaxial Compression

2018 ◽  
Vol 2018 ◽  
pp. 1-16 ◽  
Author(s):  
Zhaolin Li ◽  
Lianguo Wang ◽  
Yinlong Lu ◽  
Wenshuai Li ◽  
Kai Wang
Keyword(s):  
Acoustic Emission ◽  
Axial Strain ◽  
Triaxial Compression ◽  
Confining Pressure ◽  
Lateral Strain ◽  
Compression Tests ◽  
True Triaxial ◽  
Shear Slip ◽  
True Triaxial Compression ◽  
Triaxial Compression Tests

The study of deformation, strength, and other mechanical characteristics of sandstone under true triaxial compression is significant for understanding failure mechanisms in rock and evaluating the stability of underground structures. Conventional and true triaxial compression tests for sandstone are conducted for different stress states in this study using the self-developed true triaxial electrohydraulic servo test system combined with acoustic emission (AE) testing. This study presents an in-depth and systematic investigation of deformation, strength, and AE characteristics. The results show significant differences in deformation, strength, and acoustic emission characteristics for the rock under conventional triaxial and true triaxial compression tests, respectively. The peak strength, axial strain, lateral strain, and incremental strain (in unstable crack growth stage) increase with increasing confining pressure under conventional triaxial compression, and the AE count gradually decreases while shear crack proportion gradually increases, indicating that increasing confining pressure gradually inhibits the shear slip effect along fractures, delays perforation of the rock shear fracture surface, and enhances the ability of the rock to withstand deformation and load. Under true triaxial compression, the peak strength increases and then decreases with increasing intermediate principal stress σ2 and the axial strain ε1 and lateral strain ε2 gradually decrease; besides, the lateral strain (expansion) of the rock is mainly in the minimum principal stress σ3 direction, and lateral expansion tends to decrease before increasing. AE events first weaken and then enhance with increasing σ2, and the proportion of shear cracks increases first and then decreases, indicating that the confining pressure gradually changes from the shear slip effect that controls crack offset to the damage effect that promotes crack tension with increasing σ2. In addition, the protective effect of confining pressure improves when σ3 increases.

scholarly journals The Effect of Confining Pressure on the Mechanical Properties of Sand–Ice Materials

1973 ◽  
Vol 12 (66) ◽  
pp. 469-481 ◽  
Author(s):  
Bernard D. Alkire ◽  
Orlando B. Andersland
Keyword(s):  
Axial Strain ◽  
Triaxial Compression ◽  
Confining Pressure ◽  
Silica Sand ◽  
Creep Tests ◽  
Ice Volume ◽  
Coulomb Failure ◽  
Confining Pressures ◽  
Sand Material ◽  
Cylindrical Samples

Cylindrical samples containing 0.59 mm to 0.84 mm diameter silica sand at about 97% and 55% ice saturation (the ratio of ice volume to sand pore volume) were tested at a temperature of −12° C in triaxial compression. Both constant axial strain-rate tests and step-stress creep tests provide information on the influence of confining pressure on the shear strength and creep behavior of the sand–ice material. Changes in the degree of ice saturation help show the influence of the ice matrix versus the sand material on the mechanical behavior. Data are discussed in terms of the Mohr–Coulomb failure law and creep theories. It is shown that the cohesive component of strength depends on response of the ice matrix, whereas the frictional component of strength responds in a manner very similar to unfrozen sand tested at high confining pressures. Experimental data show that creep rates decrease exponentially and creep strength increases with an increase in confining pressure.

scholarly journals Experimental Study on Mechanical and Acoustic Emission Characteristics of Rock Samples under Different Stress Paths

2018 ◽  
Vol 2018 ◽  
pp. 1-9 ◽  
Author(s):  
Tao Qin ◽  
Hongru Sun ◽  
Heng Liu ◽  
Junwen Zhang ◽  
Tao Li ◽  
...  
Keyword(s):  
Acoustic Emission ◽  
Failure Mode ◽  
Shear Failure ◽  
Rock Specimen ◽  
Axial Strain ◽  
Failure Process ◽  
Confining Pressure ◽  
Stress Path ◽  
Initial Value ◽  
Unloading Confining Pressure

A series of tests on characteristics of acoustic emission have been performed on sandstone under uniaxial, conventional, and triaxial conditions and the unloading confining pressure path. The failure mode of rock specimen has been scanned by CT and a three-dimensional reconstruction was made. The differences on characteristics of AE, mechanics, and the failure mode of sandstone during the failure process under three paths are studied. The results show that the deformation of rock specimen is bigger, and axial strain and circumferential strain have a deformation platform at peak point of stress under the unloading confining pressure path. Characteristics of AE ringing are significantly affected by the confining pressure and stress path. AE ringing counts peak value, and accumulative ringing on the breaking moment as well as cumulative release energy is higher, which indicates that the rock failure is more violent under the unloading confining pressure path. The failure mode of rock specimen was dominated by shear failure under the conventional triaxial stress path. The tension failure is the main form at a lower initial value of unloading confining pressure, and the shear failure is more prominent at a higher initial value of unloading confining pressure.

scholarly journals Energy Evolution Law of Marble Failure Process Under Different Confining Pressures Based on Particle Discrete Element Method

2021 ◽  
Vol 8 ◽  
Author(s):  
Yan-Shuang Yang ◽  
Wei Cheng ◽  
Zhan-Rong Zhang ◽  
Hao-Yuan Tian ◽  
Kai-Yue Li ◽  
...  
Keyword(s):  
Numerical Simulation ◽  
Energy Dissipation ◽  
Axial Strain ◽  
Triaxial Compression ◽  
Failure Process ◽  
Rock Failure ◽  
Biaxial Compression ◽  
Energy Evolution ◽  
Confining Pressures ◽  
Energy Dissipated

The energy dissipation usually occurs during rock failure, which can demonstrate the meso failure process of rock in a relatively accurate way. Based on the results of conventional triaxial compression experiments on the Jinping marble, a numerical biaxial compression model was established by PFC2D to observe the development of the micro-cracks and energy evolution during the test, and then the laws of crack propagation, energy dissipation and damage evolution were analyzed. The numerical simulation results indicate that both the crack number and the total energy dissipated during the loading process increase with confining pressures, which is basically consistent with the experiment results. Two damage variables were presented in terms of the density from other researchers’ results and energy dissipation from numerical simulation, respectively. The energy-based damage variable varies with axial strain in the shape of “S,” and approaches one more closely than that based on density at the final failure period. The research in the rock failure from the perspective of energy may further understand the mechanical behavior of rocks.

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.

Comparison of Stress-Strain Relationships of FRP and Actively Confined High-Strength Concrete: Experimental Observations

2014 ◽  
Vol 919-921 ◽  
pp. 29-34 ◽  
Author(s):  
Jian Chin Lim ◽  
Togay Ozbakkloglu
Keyword(s):  
High Strength Concrete ◽  
Axial Stress ◽  
Axial Strain ◽  
High Strength ◽  
Confining Pressure ◽  
Confined Concrete ◽  
Lateral Strain ◽  
Stress Strain ◽  
Strength Concrete ◽  
Actively Confined Concrete

It is well established that lateral confinement of concrete enhances its axial strength and deformability. It is often assumed that, at a same level of confining pressure, the axial compressive stress and strain of fiber reinforced polymer (FRP)-confined concrete at a given lateral strain are the same as those in concrete actively confined concrete. To assess the validity of this assumption, an experimental program relating both types of confinement systems was conducted. 25 FRP-confined and actively confined high-strength concrete (HSC) specimens cast from a same batch of concrete were tested under axial compression. The axial stress-strain and lateral strain-axial strain curves obtained from the two different confinement systems were assessed. The results indicate that, at a given axial strain, lateral strains of actively confined and FRP-confined concretes correspond, when they are subjected to the same lateral confining pressure. However, it is observed that, at these points of intersections on axial strain-lateral strain curves, FRP-confined concrete exhibits a lower axial stress than the actively confined concrete, indicating that the aforementioned assumption is not accurate. The test results indicate that the difference in the axial stresses of FRP-confined and actively confined HSC becomes more significant with an increase in the level of confining pressure.

scholarly journals Numerical Simulation of Particle Breakage of Granular Assemblies in Discrete Element Analyses

2019 ◽  
Vol 2019 ◽  
pp. 1-17 ◽  
Author(s):  
Tao Zhang ◽  
Chi Zhang
Keyword(s):  
Total Energy ◽  
Energy Input ◽  
Axial Strain ◽  
Failure Process ◽  
Computational Cost ◽  
Confining Pressure ◽  
Discrete Element ◽  
Particle Breakage ◽  
Biaxial Tests ◽  
Total Energy Input

This paper presents numerical simulations of high-pressure biaxial tests on breakable granular soils with the discrete element method. The 2D setting is more economic in terms of computational cost, which allows simulation with a larger number of particles with a wider size distribution. The results of breakable and unbreakable agglomerates show that particle breakage has a significant influence on the macro- and micromechanical behaviors of the assembly. Higher confining pressure and larger axial strain result in the variation of particle grading and agglomerate numbers. The evolution of bond breakage during shearing makes it possible to trace the failure process and breakage mechanism at the microlevel. The breakage energy is found to account for a small fraction of total energy input compared with friction energy. A hyperbolic correlation between relative particle breakage and total energy input per unit volume was established regardless of the influence of confining pressure.

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