scholarly journals Investigation of Energy Mechanism and Acoustic Emission Characteristics of Mudstone with Different Moisture Contents

2018 ◽  
Vol 2018 ◽  
pp. 1-11 ◽  
Author(s):  
Jingdong Jiang ◽  
Jie Xu
Keyword(s):  
Acoustic Emission ◽  
Moisture Content ◽  
Total Energy ◽  
Failure Time ◽  
Triaxial Compression ◽  
Confining Pressure ◽  
Development Stage ◽  
Dissipated Energy ◽  
Deformation And Failure ◽  
Moisture Contents

Characteristics of energy accumulation, evolution, and dissipation in conventional triaxial compression of mudstones with different moisture contents were explored. Stress-strain relations and acoustic emission (AE) characteristics of the deformation and failure of rock specimens were analyzed. The densities and rates of stored energy, elastic energy, and dissipated energy under different confining pressures were confirmed. The results demonstrated that the growth rate of absorbed total energy decreases with the increase of moisture content, indicating that the higher the moisture content is, the less the total energy mudstone samples absorb. The dissipated energy of the soaking sample, by contrast, has the first increase speed, and natural sample comes second at the beginning. When entering the crack stable development stage, the dry sample has the fastest growing rate of dissipated energy, meaning that dissipated energy used for crack propagation gradually decreases with the increase of moisture content. The AE signals significantly enhance at the initial compression stage and plastic deformation stage with the moisture content decreasing. The AE location events at the failure moment decrease as the moisture content increasing. The time that the maximum AE even rate appears is slightly lagged behind the macroscopic failure time, and the AE even rates increase with the decrease of confining pressure. The above results indicate that the water erosion process on rock reduces the cohesive energy and cohesive force, destroys the micromechanical structure, and minimizes the energy states of rock.

Study on mechanical properties and damage evolution of carbonaceous shale under triaxial compression with acoustic emission

2021 ◽  
pp. 105678952199119
Author(s):  
Kai Yang ◽  
Qixiang Yan ◽  
Chuan Zhang ◽  
Wang Wu ◽  
Fei Wan
Keyword(s):  
Mechanical Properties ◽  
Acoustic Emission ◽  
Water Content ◽  
Damage Evolution ◽  
Damage Assessment ◽  
Triaxial Compression ◽  
Confining Pressure ◽  
Damage Variable ◽  
Natural State ◽  
Carbonaceous Shale

To explore the mechanical properties and damage evolution characteristics of carbonaceous shale with different confining pressures and water-bearing conditions, triaxial compression tests accompanied by simultaneous acoustic emission (AE) monitoring were conducted on carbonaceous shale rock specimens. The AE characteristics of carbonaceous shale were investigated, a damage assessment method based on Shannon entropy of AE was further proposed. The results suggest that the mechanical properties of carbonaceous shale intensify with increasing confining pressure and degrade with increasing water content. Moisture in rocks does not only weaken the cohesion but also reduce the internal friction angle of carbonaceous shale. It is observed that AE activities mainly occur in the post-peak stage and the strong AE activities of saturated carbonaceous shale specimens appear at a lower normalized stress level than that of natural-state specimens. The maximum AE counts and AE energy increase with water content while decrease with confining pressure. Both confining pressure and water content induce changes in the proportions of AE dominant frequency bands, but the changes caused by confining pressure are more significant than those caused by water content. The results also indicate that AE entropy can serve as an applicable index for rock damage assessment. The damage evolution process of carbonaceous shale can be divided into two main stages, including the stable damage development stage and the damage acceleration stage. The damage variable increases slowly accompanied by a few AE activities at the first stage, which is followed by a rapid growth along with intense acoustic emission activities at the damage acceleration stage. Moreover, there is a sharp rise in the damage evolution curve for the natural-state specimen at the damage acceleration stage, while the damage variable develops slowly for the saturated-state specimen.

Research on Hydraulic Conductivity of Coarse Sandstone under Triaxial Compression

2011 ◽  
Vol 94-96 ◽  
pp. 1146-1151 ◽  
Author(s):  
Guan Rong ◽  
Xiao Jiang Wang
Keyword(s):  
Hydraulic Conductivity ◽  
Circumferential Strain ◽  
Triaxial Compression ◽  
Confining Pressure ◽  
Test Results ◽  
Stress Strain ◽  
Deformation And Failure ◽  
Maximum Value ◽  
Strain Process ◽  
Peak Value

Permeability test for complete stress-strain process of coarse sandstone were carried out in triaxial test instrument. On the basis of test results, the influence of confining pressure and strain on the hydraulic conductivity was discussed. It is shown that in the complete stress-strain process, hydraulic conductivity changes in the law that presents the same character with the curve of stress-strain. The hydraulic conductivity reduces slightly with the increase of deviatoric stress in the stage of micro fracture compressing and elastic; In the elastoplastic stage, along with the expansion of new fractures, the hydraulic conductivity increases slowly at first and then reaches sharply to the maximum value after peak point; In the post-peak stage, the fracture which controls the hydraulic conductivity of coarse sandstone is compressed because of the confining pressure and the hydraulic conductivity decreases. During the process of deformation and failure, the hydraulic conductivity is more sensitive to the change of circumferential strain. With the increase of confining pressure, the increased value from initial to peak value and the decreased value from peak to residual value decreases.

scholarly journals Hydraulic properties and energy dissipation of deep hard rock under H-M coupling and cycling loads

2019 ◽  
Vol 23 (Suppl. 3) ◽  
pp. 935-942 ◽  
Author(s):  
Cheng-Han Zhang ◽  
Shuang You ◽  
Hong-Guang Ji ◽  
Fei Li ◽  
Hong-Tao Wang
Keyword(s):  
Acoustic Emission ◽  
Osmotic Pressure ◽  
Hydraulic Properties ◽  
Coupling Effect ◽  
High Stress ◽  
Confining Pressure ◽  
In Situ Stress ◽  
Dissipated Energy ◽  
Underground Engineering ◽  
Loading And Unloading

The permeability of deep rock is closely related to the stability and safety of underground engineering. The rocks in deep stratum are mostly with high stress and high osmotic pressure. Therefore, it is necessary to consider the coupling effect between porewater pressure and in situ stress on rock mass. A series of triaxial cyclic loading and unloading experiments under hydraulic-mechanics coupling conditions are carried out to studied the mechanical and hydraulic properties of granite in the depth of 1300 m to 1500 m. Especially, the effect of the disturbance on the permeability of fractured rocks are investigated by unloaded the confining pressure. Tests results presented that the stress-strain curves of deep granite showed typical brittle characteristics. The principal stress of granite exhibited a linear relationship under the high confining pressure of 34-40 MPa and high osmotic pressure of 13-15 MPa. Dissipated energy of the rock decreased to a relatively low level after 2-3 loading cycles and then slowly increased. Permeability showed a decreasing trend as the loading and unloading cycles increase. Finally, acoustic emission technology was used to monitor the fracture evolution in rocks, the acoustic emission signal released as the fractures develop and energy dissipated. The results would provide basic data for the exploitation and excavation in the deep galleries.

scholarly journals Effect of Stress and Moisture Content on Permeability of Gas-Saturated Raw Coal

Geofluids ◽  
2020 ◽  
Vol 2020 ◽  
pp. 1-13
Author(s):  
Junhui Wang ◽  
Zhijun Wan ◽  
Yi Wang ◽  
Zhixiang Liu ◽  
Sifei Liu ◽  
...  
Keyword(s):  
Moisture Content ◽  
Coalbed Methane ◽  
Confining Pressure ◽  
Porous Matrix ◽  
In Situ Stress ◽  
Permeability Evolution ◽  
Test Range ◽  
Moisture Contents ◽  
Volumetric Stress

Hydraulic fracturing and premining gas drainage are important to safe mining and coalbed methane extraction. These technical processes cause the redistribution of in-situ stress and the regional variation of moisture contents within the affected zone. Therefore, we investigated the coupled effect of variable stresses (from 9 MPa to 27 MPa) and moisture contents (from 0.22% to 4.00%) on the permeability evolution of gas-saturated raw coal. The results show that (1) the relationship between the mean effective stress and the permeability can be described by a power function according to the permeability evolution model of the porous matrix established in this study. Besides, the influence mechanisms of moisture on fitting coefficients in the function were analyzed. (2) The permeability decreases with the increase of in-situ stress (e.g., confining pressure or volumetric stress) in a negative exponential manner. (3) The curves of permeability variations with moisture content are not always linear, and the permeability is more sensitive to the moisture content than the volumetric stress in the test range. Moreover, the sensitivity of permeability varies in different regions. These results would be beneficial for permeability prediction and surface well parameters design.

scholarly journals Method Improvement and Effect Analysis of Triaxial Compression Acoustic Emission Test for Coal and Rock

2019 ◽  
Vol 2019 ◽  
pp. 1-10
Author(s):  
Yan Zhou ◽  
Chuanxiao Liu ◽  
Depeng Ma
Keyword(s):  
Acoustic Emission ◽  
Rock Mechanics ◽  
Triaxial Compression ◽  
Confining Pressure ◽  
Outer Wall ◽  
Test System ◽  
Test Method ◽  
Effect Analysis ◽  
High Confining Pressure ◽  
Ae Signals

In the study of the acoustic emission (AE) characteristics of rock samples or coal samples under triaxial compression conditions, most scholars carry out relevant experiments by placing the AE detector on the outer wall of the triaxial chamber of the rock mechanics test system. Owing to the continuous obstruction of AE signals by hydraulic oil in the triaxial chamber and the frequent interference of external noises, the final experimental data cannot objectively and truly reflect the essential characteristics of AE of rock or coal under triaxial compression conditions. It is difficult to scientifically guide and accurately predict precursory information of rock’s or coal’s rupture and instability. Based on this, a series of improvements and optimizations were made to the original triaxial compression AE test method, which is based on the modification of the communication interface of the rock mechanics test system, a test head which can put the AE detector into the triaxial chamber and withstands high confining pressure, in order to obtain the true, comprehensive, and reliable AE signals. It is of considerable significance to the scientific determination of the precursory characteristics of rock’s or coal’s rupture and instability.

scholarly journals Disturbance Evolution Behavior of Loess Soil under Triaxial Compression

2020 ◽  
Vol 2020 ◽  
pp. 1-14
Author(s):  
Yali Xu ◽  
Panpan Guo
Keyword(s):  
Triaxial Compression ◽  
Deformation Modulus ◽  
Loess Soil ◽  
Confining Pressure ◽  
Compression Tests ◽  
Structural Effects ◽  
Moisture Contents ◽  
Confining Pressures ◽  
Evolution Behavior ◽  
Disturbance Function

This paper presents an investigation into the evolution law of the structural effects of Xi’an loess soil, based on the disturbed state concept. First, a series of consolidated and drained triaxial compression tests were performed on undisturbed and remoulded loess samples prepared at five different moisture contents and tested at four different confining pressures. Second, two disturbance functions with different parameters were proposed to quantify mathematically the structural effects of loess. Finally, the proposed disturbance functions were validated against documented test results by other researchers. The results indicated that the single-parameter disturbance function, with the deformation modulus as its parameter, provides convenience for application but takes no account of the respective contributions of deviatoric stress and mean stress to the disturbance evolution behavior of loess. The double-parameter disturbance function, with the shear and bulk moduli as its parameters, is capable of distinguishing these respective contributions and reflects well the disturbance evolution behavior of loess under various moisture contents and confining pressures. The effects of moisture content and confining pressure on the parameters of the disturbance functions were found to be unsteady. The proposed disturbance functions lay the foundation for establishing a constitutive model for loess accounting for the structural effect.

scholarly journals Study on the Mechanical Behavior and Acoustic Emission Properties of Granite under Triaxial Compression

Geofluids ◽  
2021 ◽  
Vol 2021 ◽  
pp. 1-17
Author(s):  
Jiaqi Guo ◽  
Pengfei Liu ◽  
Junqi Fan ◽  
Hengyuan Zhang
Keyword(s):  
Acoustic Emission ◽  
Crack Initiation ◽  
Triaxial Compression ◽  
Testing Machine ◽  
Confining Pressure ◽  
High Energy ◽  
Granite Sample ◽  
Initiation Point ◽  
Granite Samples ◽  
Ae Signals

To study the rock mechanical behaviors and damage process mechanism of granite samples under triaxial stress, conventional triaxial compression tests were carried out on an RMT-150B rock mechanics testing machine and acoustic emission detector. The test results show that the strength of the granite sample has a good linear relationship with the confining pressure, the cohesion force c of the granite samples is 29.37 MPa, and the internal friction angle is 54.23° by calculation based on the Mohr-Coulomb strength criterion. The larger the initial confining pressure of the rock sample is, the larger the crack initiation stress ( σ ci ) and dilatancy stress ( σ cd ) of the granite specimen are, the larger the energy values at the crack initiation point and dilatancy point are, and the larger the peak energy storage and energy release rate at the failure are. In the case of a small initial confining pressure, the AE ringdowning counts and the cumulative AE ringing counts increase to their maximum instantaneously at the peak stress point, and the damage of the sample develops rapidly. While the initial confining pressure is high, the AE ringing counts and the cumulative AE ringing counts of the granite specimens increase evenly, and the deformation damage of the granite specimens is slow. Before the crack initiation point, AE signals are mainly low-energy and low-frequency friction-type AE events, while after the dilatation point, AE signals of samples are mainly high-frequency and high-energy fracture-type AE events. The failure mode of granite samples judged by acoustic emission parameters according to the distribution of characteristic values of AE parameters RA and AF is consistent with the reality. The AE b value of the granite sample is large when the confining pressure is low, and there will be a sudden drop, the decrease time is late, and the decrease rate is large. Under the same stress level, the larger the confining pressure is, the larger the damage variable D is.

Experimental Study of the Creep Disturbance Effect and Acoustic Emission Characteristics of Mudstone with Different Moisture Contents

2021 ◽  
Vol 2021 ◽  
pp. 1-8
Author(s):  
Yongjiang Yu ◽  
Pengbo Wang ◽  
Shipeng Zhang ◽  
Jingjing Liu
Keyword(s):  
Acoustic Emission ◽  
Moisture Content ◽  
Soft Rock ◽  
Clear Understanding ◽  
Creep Failure ◽  
Soft Rocks ◽  
Moisture Contents ◽  
Accelerated Creep ◽  
The Stability ◽  
The Impact

It is important to have a clear understanding of the creep characteristics of water-rich soft rocks under a dynamic load and the evolution of cracks because soft rock roadways in deep mines are very sensitive to disturbances, and instability and damage can easily occur under the impact of disturbances such as mining and blasting. In this study, a self-developed disturbed creep test bench was used to conduct graded loading creep disturbance tests on mudstone specimens with different moisture contents. The results show that an increase in the moisture content leads to a significant increase in the creep failure strain of mudstone, and the accelerated creep rate is greatly accelerated. Moreover, as the moisture content increases, the type of mudstone creep disturbance failure gradually changes from accelerated creep failure to disturbance failure. By analyzing the acoustic emission (AE) characteristics of the mudstone creep disturbance tests, it was found that the increase in the moisture content greatly weakens the AE count and the accumulated energy. In each stage of disturbance, the AE signals jumped, and the stability was restored at the end of the disturbance. As the load increased, the specimen entered the accelerated creep stage, the AE signal increased exponentially, and the internal cracks expanded rapidly until failure occurred. It is of great significance to carry out creep disturbance experiments and to analyze the evolution of the internal cracks in specimens with different moisture contents to maintain the long-term stability of deep soft rocks.

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 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.

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