scholarly journals Acoustic Emission Characteristics of Graded Loading Intact and Holey Rock Samples during the Damage and Failure Process

2019 ◽  
Vol 9 (8) ◽  
pp. 1595 ◽  
Author(s):  
Xiaofei Liu ◽  
Huajie Zhang ◽  
Xiaoran Wang ◽  
Chong Zhang ◽  
Hui Xie ◽  
...  
Keyword(s):  
Acoustic Emission ◽  
Rock Mass ◽  
Large Scale ◽  
Rock Sample ◽  
Axial Stress ◽  
Failure Process ◽  
Dynamic Monitoring ◽  
Rock Samples ◽  
General Law ◽  
Ae Counts

Rock burst is the result of the development and extension of micro-cracks during the loading process of large-scale rock mass in underground space engineering. Dynamic monitoring results by acoustic emission (AE) can accurately perceive the inner fracture evolution of rock mass and effectively warn about its induced disasters early. By contrastive testing the AE parameters in the whole fracture process of the intact and holey rock samples under graded loading, their spatiotemporal evolution rules were analyzed in this paper, and the damage model of rock samples based on AE localization events was established to analyze the relationship between rock damage and loads. The results show that: (1) Under the condition of grading loading, AE parameter increases with the increase of axial stress and show three states, respectively, which are slow-growth, stabilization and rapid increasing; meanwhile, the damage of the sample has a cumulative effect with time. (2) The AE counts and energy are highly correlated with the fracture of the sample that the more severe the damage of the sample, the faster the crack propagation as well as the higher the acoustic emission counts and the energy amplitude. The damage state of granite sample can be accurately judged by two parameters to character the damage evolution process and fracture mechanism. (3) Compared with the intact rock sample, due to the pressure relief effect of the hole, the rock sample containing the hole takes a long time in the compaction stage and with higher load stress level. Although the AE counts and energy were lower in the damage process, the general law of their response during damage and instability process still exists.

Model Testing and Analysis Study on Shear Strength of Rock Mass Containing Multiple Cracks under Compression-Shearing Loading

2008 ◽  
Vol 33-37 ◽  
pp. 617-622
Author(s):  
Wei Shen Zhu ◽  
Bin Sui ◽  
Wen Tao Wang ◽  
Shu Cai Li
Keyword(s):  
Shear Strength ◽  
Rock Mass ◽  
Rock Sample ◽  
Failure Process ◽  
Jointed Rock ◽  
Multiple Cracks ◽  
Test Results ◽  
Failure Model ◽  
Two Phase ◽  
Bridge Failure

Two-phase modelling testing was performed to study the shear strength of rock bridges of jointed rock mass in this paper. The failure process of rock sample containing multiple collinear cracks was observed. Based on theory of fracture mechanics and analytical method, a rock-bridge failure model was proposed and the expression of shear strength was derived. Comparison of calculated shear strength and the model test results was made and they agree well.

scholarly journals Stress Drop as a Result of Splitting, Brittle and Transitional Faulting of Rock Samples in Uniaxial and Triaxial Compression Tests

2015 ◽  
Vol 37 (1) ◽  
pp. 17-23 ◽  
Author(s):  
Jerzy Cieślik
Keyword(s):  
Stress Drop ◽  
Rock Sample ◽  
Triaxial Compression ◽  
Failure Process ◽  
Strength Loss ◽  
Axial Stiffness ◽  
Compression Tests ◽  
Rock Samples ◽  
Test Pressure ◽  
Triaxial Compression Tests

Abstract Rock samples can behave brittle, transitional or ductile depending on test pressure, rate of loading and temperature. Axial stiffness and its changes, relative and absolute dilatancy, yield, and fracture thresholds, residual strength are strongly pressure dependent. In this paper the stress drop as an effect of rock sample strength loss due to failure was analyzed. Uniaxial and triaxial experiments on three types of rock were performed to investigate the stress drop phenomenon. The paper first introduces short background on rock behavior and parameters defining a failure process under uniaxial and triaxial loading conditions. Stress drop data collected with experiments are analyzed and its pressure dependence phenomenon is described. Two methods for evaluation of stress drop value are presented.

scholarly journals Study on the Dynamic Response Characteristics of Cylindrical Coal-Rock Samples under Dynamic Loads

2020 ◽  
Vol 2020 ◽  
pp. 1-12
Author(s):  
Hongqing Zhu ◽  
Shuhao Fang ◽  
Yilong Zhang ◽  
Yan Wu
Keyword(s):  
Dynamic Response ◽  
Linear Relationship ◽  
Rock Sample ◽  
Axial Stress ◽  
Stress And Strain ◽  
Rock Samples ◽  
Response Characteristics ◽  
Coal Rock ◽  
Dynamic Response Characteristics ◽  
The Impact

To research the dynamic response characteristics of cylindrical coal-rock samples under impact loads, the impact of rigid bars on cylindrical coal-rock samples is simulated under different speed conditions, based on LS-DYNA software, and the dynamic distribution characteristics of the stress, strain, and energy of cylindrical coal-rock samples are analyzed. The results demonstrated the following: (1) the cylindrical coal-rock sample failed at the center first, and the damage developed downward along the axial direction. (2) The critical effective stress and strain have an exponential function relationship with the velocity, and the critical time has a linear relationship with the velocity. (3) The energy change law of the cylindrical coal-rock sample is consistent with the destruction morphology. (4) The axial stress peaks in the severe damage part have a linear relationship with the speed, the axial stress attenuates rapidly after passing the stress yield point, and the axial strain does not increase continuously. (5) The peaks stress and strain on the central axis and the radial line obey the power function distribution, the axial stress produces tensile stress in the axial propagation direction, and the axial stress and strain peaks at the same position are larger than those of the radial stress and strain peaks. This research provides a reference for studying coal and rock dynamic disasters.

scholarly journals Creep Structure Effect of Layered Rock Mass Based on Acoustic Emission Characteristics

2021 ◽  
Vol 2021 ◽  
pp. 1-14
Author(s):  
Huichen Xu ◽  
Yong Zhang ◽  
Chengwei Zhao ◽  
Chengyu Miao ◽  
Xiaoming Sun
Keyword(s):  
Acoustic Emission ◽  
Rock Mass ◽  
Inclination Angle ◽  
Stress Level ◽  
Rock Sample ◽  
Structural Effect ◽  
Emission Characteristics ◽  
Structural Effects ◽  
Layered Rock ◽  
Layered Rock Mass

Investigating the creep structural effect of layered rock mass is of great practical and theoretical significance. In this paper, taking the Muzhailing tunnel as an example, structure effect of layered rock mass based on acoustic emission characteristics has been analyzed. The study shows that creep parameters of layered rock mass are significantly influenced by structural effects, and the overall creep variable is small. The creep deformation of layered rock mass includes transient creep and steady-state creep at a low stress level. At a higher stress level, when the long-term strength of the rock sample is reached, the deformation increases rapidly, and the accelerated creep occurs in a very short period of time. The creep equation of the structural effects of layered rock mass was established based on the experimental results. Acoustic emission characteristics are analyzed during creep experiment; the study shows that the energy released at the time of initial loading and destruction accounted for most of the total energy. The initial energy release increased first and then decreased with the increase in inclination angle; as the inclination angle increased, the cumulative energy when the rock sample was damaged first decreased and then increased. The structural effect on the main frequency value at the time of failure mainly reflected in the trend that the main frequency value first increased and then decreased as the inclination angle increased. Based on the above analysis, we can recognize the structural effects of layered rock mass and provide the necessary parameters for on-site support.

scholarly journals Failure Prediction of Two Types of Rocks Based on Acoustic Emission Characteristics

2019 ◽  
Vol 2019 ◽  
pp. 1-11
Author(s):  
Bing Sun ◽  
Shanshan Hou ◽  
Jiehui Xie ◽  
Sheng Zeng
Keyword(s):  
Acoustic Emission ◽  
Rock Mass ◽  
Stability Analysis ◽  
Rock Burst ◽  
Uniaxial Compression ◽  
Failure Process ◽  
Energy Curve ◽  
Characteristic Parameters ◽  
Cumulative Energy ◽  
The Stability

The stability analysis of rock is an important basis to ensure the safe exploitation of underground resources and the reliable operation of space engineering. Uniaxial compression and acoustic emission (AE) tests were carried out on two common rock samples with strong rock burst tendency. The relationship between mechanical characteristics, AE characteristics, and rock burst tendency in the failure process of rock with different body types and the evolution of fractal characteristics of AE parameters were discussed. Based on the cusp mutation theory, the catastrophe model of AE characteristic parameters was established to quantify the instability mechanism of rock mass. The results show that the AE mutation rate (AEMR) of the cubic specimens increase from a low level to a high level gradually in the stable fracture stage, while that of the cylindrical specimens increase sharply to the maximum when the specimens are near failure. The AE cumulative energy curves of cubic specimens show a “step” rise, while that of cylindrical specimens show a “gradual” rise, and the rock burst process of cubic specimens is faster. The fractal dimension evolution mode of AE characteristic parameters of cubic specimens during uniaxial compression text is decline-rise-decline, while that of cylindrical specimen is decline-rise-decline-steeply rise. According to the periodic change of AE cumulative energy curve, combined with the rock failure cusp mutation model, the occurrence of rock burst can be well predicted, providing certain theoretical guidance for the stability analysis of underground engineering rock mass.

scholarly journals Research on the Impact of Different Force Directions on the Mechanical Properties and Damage Evolution Law of Sandstone with Different Hole Diameters

2021 ◽  
Vol 2021 ◽  
pp. 1-14
Author(s):  
Fukun Xiao ◽  
Renhe Li ◽  
Le Xing
Keyword(s):  
Mechanical Properties ◽  
Acoustic Emission ◽  
Energy Conversion ◽  
Rock Sample ◽  
Strain Curve ◽  
Hole Diameter ◽  
Stress Strain Curve ◽  
Rock Samples ◽  
The Impact ◽  
Vertical Hole

In this research, a uniaxial acoustic emission experiment was conducted on rock samples with different positions and diameters of the hole, and an analysis was made on the impact of different hole positions and diameters on the mechanical properties, failure, energy conversion, and acoustic emission-caused damage characteristics and laws of the rock samples. The results reveal as follows: first, due to the existence of holes in rocks, the stress-strain curve changes at each stage, accompanied by multiple stress drops. And the peak strength gradually reduces with the increase in hole diameter. At different hole positions, the duration that the rock sample passes through at each stage of the stress-strain curve varies, and the peak strength of the rock with the vertical hole is greater than that of the rock with the horizontal hole. This indicates that the bearing capacity and stability of the rock sample with the vertical hole are greater than those of the rock sample with the horizontal hole of the same diameter. Second, by making a comparison on the failure characteristics of rock samples, it is found that the intact rock shows brittle failure. For the rock sample with the horizontal hole, symmetrical tensile cracks initially appear in the upper and lower parts of the hole and finally form shear failure. As for the rock sample with the vertical hole, Y-shape failure originally presents and eventually forms N-shape failure with the increase in hole diameter. Over a comparison with the failure pattern of an intact rock sample, it is demonstrated that the final failure pattern and crack expansion trend on the rock sample vary with the change in the hole position and diameter. Third, as obtained by comparing and analyzing the energy conversion of the rock with different diameters of the hole, the energy conversion in the rock is changed due to the existence of holes, and the increase in hole diameter causes a gradual decrease in the elastic energy stored in the rock and gradual increase in the dissipated energy. And by comparing the energy conversion of the rock with different positions of the hole, it is acquired that the elastic energy conversion ratio of the rock with the vertical hole is higher than that of the rock with the horizontal hole. Furthermore, an explanation was made on the difference in the failure processes of the two types of rocks from the perspective of energy conversion.

scholarly journals Effect of Thermal Treatment on Fractals in Acoustic Emission of Rock Material

2016 ◽  
Vol 2016 ◽  
pp. 1-9 ◽  
Author(s):  
Z. Z. Zhang ◽  
X. L. Xu ◽  
Q. P. Sun ◽  
Y. Dong
Keyword(s):  
Acoustic Emission ◽  
Stress Level ◽  
Failure Process ◽  
Fractal Dimensions ◽  
Rock Material ◽  
External Loading ◽  
Heat Temperature ◽  
Failure Point ◽  
Ae Counts ◽  
Peak Value

Acoustic emission (AE) series on time and location distributions on space are all fractal during the failure process of rock material. In this paper, AE signals of heated rock samples at different temperature under uniaxial compression were captured, and the correlation fractal dimensions (CFDs) of AE counts series at different stress level were calculated using Grassberger-Procaccia algorithm. The temperature effect on AE fractal behavior was revealed. The results show that as the heat temperature increases, the total AE counts are more, while the peak value is less. With the increase of external loading, the AE CFD increases fast to a peak at first and then decreases to a bottom and, after that, increases again but within a narrow range. 200°C and 800°C are two thresholds. As the heat temperature rises, the maximum CFD value and the corresponding stress level both increase from 25°C to 200°C and decrease from 200°C to 800°C and then increase again from 800°C to 1200°C. The CFD value at the failure point shows polynomial decline with rising heat temperature.

scholarly journals Experimental Research on Brittleness and Rockburst Proneness of Three Kinds of Hard Rocks under Uniaxial Compression

2021 ◽  
Vol 2021 ◽  
pp. 1-10
Author(s):  
Rongchao Xu ◽  
Yiding Jin ◽  
Yumin Zhang
Keyword(s):  
Acoustic Emission ◽  
Uniaxial Compression ◽  
Fracture Mechanism ◽  
Large Scale ◽  
Rock Fracture ◽  
Failure Process ◽  
High Energy ◽  
Brittle Rock ◽  
Evaluation Index ◽  
Unstable Crack

Rockburst is a highly destructive geological disaster caused by excavation and unloading of hard and brittle rock mass under high geostress environment. Quantitative evaluation of rock brittleness and rockburst proneness is one of the important tasks in potential rockburst assessment. In this study, uniaxial compression and acoustic emission tests were carried out for basalt, granite, and marble, and their brittleness and rockburst proneness were quantitatively evaluated. The acoustic emission evolution characteristics of the three rocks during uniaxial compression were analyzed, and the differences of fracture mechanism of the three rocks were compared. The results show that (1) based on the brittleness evaluation index, basalt is the most brittle rock, followed by granite, and marble is the weakest; (2) based on the rockburst proneness evaluation index, combined with the macroscopic failure phenomenon and morphology of the samples, the rockburst proneness of basalt is the strongest, followed by granite, and marble is the weakest; (3) there exists a positive correlation between rockburst proneness and brittleness, and the fitting results show that they are approximately exponential; and (4) brittleness has an important influence on the rock fracture mechanism. Unlike marble, basalt and granite with strong brittleness continuously present high-energy acoustic emission signals in the stage of unstable crack propagation, and large-scale fracture events continue to occur; from the calculation results of the acoustic emission b value, the stronger the brittleness of rock, the larger the proportion of large-scale fracture events in the failure process.

Numerical Simulation on Cracks Propagation and Coalescence Process in Rock

2007 ◽  
Vol 353-358 ◽  
pp. 933-936 ◽  
Author(s):  
Deng Pan Qiao ◽  
Ya Ning Sun ◽  
Shu Hong Wang ◽  
Juan Xia Zhang
Keyword(s):  
Numerical Simulation ◽  
Rock Mass ◽  
Rock Sample ◽  
Failure Process ◽  
High Stress ◽  
Rock Failure ◽  
Coalescence Process ◽  
Direction Parallel ◽  
Rock Failure Process ◽  
Cracks Propagation

The failure of rock mass under loading is resulting from preexisting flaws, such as cracks, pores and other defects. However, the propagation and coalescence mechanism among multi-group cracks is still a puzzle, especially to the engineering rocks in site. In this study, the failure of rock samples with two groups of preexisting parallel cracks under the axial load were numerically investigated by the Rock Failure Process Analysis code (RFPA) from a mechanics point of view. The simulated results reproduce the rock failure process: at the first loading stage, the particle is stressed and energy is stored as elastic strain energy with a few randomly isolated fractures. As the load increases, the isolated fractures are localized to form a macroscopic crack. At the peak load, the isolated fractures unstably propagate in a direction parallel to the loading direction following tortuous paths and with numerous crack branches. Finally, the major crack passes through the rock sample and several coarse progeny cracks are formed. Moreover, in the vicinity of the contacting zone the local crushing is always induced to cause fines. On the base of the simulated results, it is found that the dominant breakage mechanisms are catastrophic splitting and progressive crushing. It is pointed out that the particle breakage behavior strongly depends on the heterogeneous material property, the irregular shape and size, and the various loading conditions. Because of heterogeneity, the crack propagates in tortuous path and crack branching becomes a usual phenomenon. The failure process of rock sample demonstrated that due to the high stress concentration at the cracks tip or some weaker strength elements which are not on the cracks surface initiate some micro-fractures, those cracks and fractures may gradually become larger and larger, more and more with the progress of loading so that join into the branch cracks leading to the rock failure in the end. Not only did the output of the numerical simulation study compare well with the experiment results, but also the further insights of the mechanism of cracks propagation and coalescence process in rock mass were obtained.

In Situ Tests on Creep Behavior of Rock Mass with Joint or Shearing Zone in Foundation of Large-Scale Hydroelectric Projects

2004 ◽  
Vol 261-263 ◽  
pp. 1097-1102 ◽  
Author(s):  
Jian Liu ◽  
Xia Ting Feng ◽  
Xiu Li Ding ◽  
Huo Ming Zhou
Keyword(s):  
Rock Mass ◽  
Creep Behavior ◽  
Large Scale ◽  
Time Dependent ◽  
Three Gorges Project ◽  
Three Gorges ◽  
The Three Gorges ◽  
The Three Gorges Project

The time-dependent behavior of rock mass, which is generally governed by joints and shearing zones, is of great significance for engineering design and prediction of long-term deformation and stability. In situ creep test is a more effective method than laboratory test in characterizing the creep behavior of rock mass with joint or shearing zone due to the complexity of field conditions. A series of in situ creep tests on granite with joint at the shiplock area of the Three-Gorges Project and basalt with shearing zone at the right abutment of the Xiluodu Project were performed in this study. Based on the test results, the stress-displacement-time responses of the joints and basalt are analyzed, and their time-dependent constitutive model and model coefficients are given, which is crucial for the design to prevent the creep deformations of rock masses from causing the failure of the operation of the shiplock gate at the Three-Gorges Project and long-term stability of the Xiluodu arc dam.

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