scholarly journals Seismic b-Value for Foreshock AE Events Preceding Repeated Stick-Slips of Pre-Cut Faults in Granite

2018 ◽  
Vol 8 (12) ◽  
pp. 2361 ◽  
Author(s):  
Xinglin Lei ◽  
Shinian Li ◽  
Liqiang Liu
Keyword(s):  
Shear Stress ◽  
Dynamic Range ◽  
Triaxial Compression ◽  
Sampling Rate ◽  
Maximum Amplitude ◽  
Seismic Hazard Assessment ◽  
Confining Pressure ◽  
B Value ◽  
Stick Slip ◽  
Shear Rupture

In this study, the b-values for acoustic emission (AE) events during stick-slip cycles of pre-cut faults in granite (as an analogue of unfavorably oriented immature faults) under triaxial compression (confining pressure: 40 MPa) are investigated. Using a multi-channel AE waveform recording system and two peak detectors, we recorded AE waveforms at 16 bits and at a sampling rate of 25 MHz, as well as the maximum amplitude of AE events with a dynamic range of 55 dB. For stick-slip events, the b-value decreases from 1.2 to 1.5 to approximately 0.6 as the shear stress increases, and then quickly jumps back to 1.0 to 1.3 immediately prior to the dynamic stress drop. The minimum b-value coincides with the maximum event rate and a stress level of 70 to 95% of the shear strength. It is also observed that the AE activity during each cycle was linked with the pre-failure fault slip, which accounts for 30% of the dynamic slip. Our results on b-value evaluation preceding repeated stick-slips can be used as an indicator of the degree of fault maturity and shear stress acting on the fault, which is important in seismic hazard assessment and earthquake prediction, especially for the injection-induced seismicity for fields in which reactivated shear rupture of unfavorable and immature faults or tensile fractures is important.

scholarly journals Evolution of b-Value and Fractal Dimension of Acoustic Emission Events During Shear Rupture of an Immature Fault in Granite

2019 ◽  
Vol 9 (12) ◽  
pp. 2498 ◽  
Author(s):  
Xinglin Lei
Keyword(s):  
Acoustic Emission ◽  
Fractal Dimension ◽  
Event Rate ◽  
Triaxial Compression ◽  
Maximum Amplitude ◽  
B Value ◽  
Relative Magnitude ◽  
Fault Reactivation ◽  
P Wave ◽  
Shear Rupture

The present study investigated the evolutions of b-value and fractal dimension of acoustic emission (AE) events during shear rupture of a naturally-created rough fracture in a granite specimen under triaxial compression. Acoustic emission signals were monitored by 16 sensors mounted directly on the surface of the specimen, and AE waveforms were sampled at 16 bits and 25 MHz. Reliable hypocenters were determined using P-wave arrival times picked up from the waveforms. Acoustic emission magnitude was determined from the maximum amplitude monitored by two peak detectors, which have a relative magnitude range of 0 to 2.75. A three-dimensional X-ray computed tomography scan was performed after the test to explore the fracture geometry. Acoustic emission activity was initiated during hydrostatic compression. With increasing differential stress, AEs demonstrated an increasing event rate, a decrease (from approximately 1.8 to 1.6) with a subsequent precursory increase (from 1.6 to 1.8) in fractal dimension, a quick decrease in b-value (from 1.0 to approximately 0.5), and a quick increase in fractal dimension (from 1.8 to 2.0). The exponentially increasing event rate, gradually decreasing b-value, and slowly increasing fractal dimension may be an intermediate-term indication of fault reactivation. In contrast, a progressively increasing event rate, a rapid drop in b-value, and a rapid increase in fractal dimension may facilitate short-term prediction of large events, which reflect the rupture of large patches. Acoustic emission hypocenters were clustered on the entire fracture surface. The present study sheds some light on detecting early signs of fault reactivation by monitoring injection-induced seismicity in areas with faults of different maturity.

scholarly journals Analysis of energy characteristics of acoustic emission signals during uniaxial compression of geomaterial samples

2020 ◽  
Vol 196 ◽  
pp. 02004
Author(s):  
Vladimir Sychev ◽  
Leonid Bogomolov ◽  
Dmitriy Kulkov
Keyword(s):  
Acoustic Emission ◽  
Energy Distribution ◽  
Uniaxial Compression ◽  
Sampling Rate ◽  
Maximum Amplitude ◽  
Low Noise ◽  
Distribution Functions ◽  
Stick Slip ◽  
Ae Signal ◽  
Ae Signals

Acoustic emission (AE) signals were obtained during deformation by uniaxial compression of specimens of various geomaterials. Experiments on uniaxial compression were carried out on a low-noise lever setup with water leakage, where the maximum load on the sample does not exceed 250 kN. The received signals were digitized by an 8-channel USB 3000 ADC unit with a width of 14 bits and a maximum sampling rate of 3 MHz. The energy distribution functions of AE signals are considered. The maximum amplitude of the AE waveform was selected as the energy characteristic of the AE signal. The flow of AE events is considered from the viewpoint of nonequilibrium thermodynamics using the Tsallis statistics. To describe the energy distribution function of the AE signals, we used a modified model of a stick-slip earthquake source -”discontinuous sliding” of two plates over each other along a fault in the presence of friction and the principle of maximum entropy. The model is used to quantify long-range correlations arising in the flow of earthquakes. It is shown that the AE signal flow is a system with memory and longrange correlations. The analysis of the behavior of the Tsallis parameter was carried out throughout the experiment.

The Strength and Stress-Strain Characteristics of Oakdale Coal under Triaxial Compression

1960 ◽  
Vol 97 (5) ◽  
pp. 422-435 ◽  
Author(s):  
D. W. Hobbs
Keyword(s):  
Shear Stress ◽  
Normal Stress ◽  
Elastic Strain ◽  
Triaxial Compression ◽  
Confining Pressure ◽  
Laboratory Measurements ◽  
Stress Concentrations ◽  
Stress Strain ◽  
Coking Coal ◽  
Local Edge

AbstractLaboratory measurements of the effect of a confining pressure on the strength and stress-strain characteristics of a metallurgical coking coal are described. Several-fold increases in the strength, the Young's modulus and the elastic strain at failure were found as the confining pressure was increased to 5,000 lb./n.2. The results are discussed in relation to various criteria of failure. It was found that failure was represented by Coulomb's equation relating shear stress and normal stress, provided the observed angles of fracture were not influenced by local edge stress concentrations.

scholarly journals Numerical Investigation on the Triaxial Compression Behavior of Large-Scale Jointed Coal

2021 ◽  
Author(s):  
Xiaoqing Wang ◽  
Fuqiang Gao
Keyword(s):  
Elastic Modulus ◽  
Triaxial Compression ◽  
Confining Pressure ◽  
Joint Effect ◽  
Coal Mass ◽  
Lateral Strain ◽  
Accurate Estimation ◽  
Rupture Surface ◽  
Compression Behavior ◽  
Shear Rupture

Abstract Accurate estimation of the triaxial compression behavior of coal mass is essential for coal mining. In this study, a numerical synthetic rock mass method was used to study the triaxial compression behavior of coal mass. The jointed-coal specimens were constructed based on in-situ joint measurements and microparameter calibration against laboratory tested data. A series of triaxial compression tests on jointed-coal specimens with different loading orientations and confining pressures were performed to obtain joint and confining-pressure effects and to reveal the related failure mechanism. The results suggest that jointed coal has a strong joint effect and confining-pressure effect. Joints weaken the strength and elastic modulus, reduce the lateral deformation, and affect the geometries of the shear-rupture surface. With increase in the confining pressure, the peak strength and residual strength increase but the elastic modulus remains stable; the lateral strain decreases, especially at low confining pressure; the mechanical behavior transitions from brittleness to ductility; the failure mode transitions from shear-rupture surface to plastic flow; and the joint effect diminishes and even disappears. The shear-rupture surface is formed by the combined effect of shear stress and joints at low confining pressure, and the contribution of joints decreases with increase in confining pressure.

The frequency-magnitude relation of microfracturing in rock and its relation to earthquakes

1968 ◽  
Vol 58 (1) ◽  
pp. 399-415 ◽  
Author(s):  
C. H. Scholz
Keyword(s):  
Crustal Deformation ◽  
Elastic Waves ◽  
Laboratory Experiments ◽  
Rock Type ◽  
Triaxial Compression ◽  
Confining Pressure ◽  
B Value ◽  
Compression Tests ◽  
Triaxial Compression Tests ◽  
Frequency Magnitude

abstract During the deformation of rock in laboratory experiments, small cracking events, i.e., microfractures, occur which radiate elastic waves in a manner similar to earthquakes. These radiations were detected during uniaxial and triaxial compression tests and their frequency-magnitude relation studied. They were found to obey the Gutenberg and Richter relation log N = a + b M Where N is the number of events which occurred of magnitude M, and a and b constants. The dependence of the parameter b on rock type, stress, and confining pressure was studied. It was found to depend primarily on stress, in a characteristic way. The frequency-magnitude relation for events which accompanied frictional sliding and deformation of a ductile rock was found to have a much higher b value than that observed in brittle rock. The Gutenberg and Richter formulation of the frequency-magnitude relation was derived from a statistical model of rock and crustal deformation. This analysis demonstrates the basis of similarity between rock deformation experiments in the laboratory and deformation of the crust.

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.

scholarly journals Prediction Models of Shear Parameters and Dynamic Creep Instability for Asphalt Mixture under Different High Temperatures

Polymers ◽  
2021 ◽  
Vol 13 (15) ◽  
pp. 2542
Author(s):  
Junxiu Lv ◽  
Xiaoyuan Zhang
Keyword(s):  
Shear Stress ◽  
Shear Strength ◽  
Stress Level ◽  
Prediction Models ◽  
Asphalt Mixture ◽  
Confining Pressure ◽  
Shear Strength Parameters ◽  
Dynamic Creep ◽  
Shear Stress Level ◽  
Creep Instability

This study mainly investigates the prediction models of shear parameters and dynamic creep instability for asphalt mixture under different high temperatures to reveal the instability mechanism of the rutting for asphalt pavement. Cohesive force c and internal friction angle φ in the shear strength parameters for asphalt mixture were obtained by the triaxial compressive strength test. Then, through analyzing the influence of different temperatures on parameters c and φ, the prediction models of shear strength parameters related to temperature were developed. Meanwhile, the corresponding forecast model related to confining pressure and shear strength parameters was obtained by simplifying the calculation method of shear stress level on the failure surface under cyclic loading. Thus, the relationship of shear stress level with temperature was established. Furthermore, the cyclic time FN of dynamic creep instability at 60 °C was obtained by the triaxial dynamic creep test, and the effects of confining pressure and shear stress level were considered. Results showed that FN decreases exponentially with the increase in stress levels under the same confining pressure and increases with the increase in confining pressure. The ratio between shear stress level and corresponding shear strength under the same confining pressure was introduced; thus, the relationship curve of FN with shear stress level can eliminate the effect of different confining pressures. The instability prediction model of FN for asphalt mixture was established using exponential model fitting analysis, and the rationality of the model was verified. Finally, the change rule of the parameters in the instability prediction model was investigated by further changing the temperature, and the instability forecast model in the range of high temperature for the same gradation mixture was established by the interpolation calculation.

Assessment of Inherent Anisotropy and Confining Pressure Influences on Mechanical Behavior of Anisotropic Foliated Rocks Under Triaxial Compression

2015 ◽  
Vol 49 (6) ◽  
pp. 2155-2163 ◽  
Author(s):  
Davood Fereidooni ◽  
Gholam Reza Khanlari ◽  
Mojtaba Heidari ◽  
Ali Asghar Sepahigero ◽  
Amir Pirooz Kolahi-Azar
Keyword(s):  
Mechanical Behavior ◽  
Triaxial Compression ◽  
Confining Pressure ◽  
Inherent Anisotropy

Mechanical behaviour of powders using a medium pressure flexible boundary cubical triaxial tester

2003 ◽  
Vol 217 (3) ◽  
pp. 233-241 ◽  
Author(s):  
F Li ◽  
V M Puri
Keyword(s):  
Shear Modulus ◽  
Mechanical Behaviour ◽  
Triaxial Compression ◽  
Three Dimensional ◽  
Volumetric Strain ◽  
Confining Pressure ◽  
Alumina Powder ◽  
Medium Pressure ◽  
Mean Pressure ◽  
Confining Pressures

A medium pressure (<21 MPa) flexible boundary cubical triaxial tester was designed to measure the true three-dimensional response of powders. In this study, compression behaviour and strength of a microcrystalline cellulose powder (Avicel® PH102), a spray-dried alumina powder (A16SG), and a fluid-bed-granulated silicon nitride based powder (KY3500) were measured. To characterize the mechanical behaviour, three types of triaxial stress paths, that is, the hydrostatic triaxial compression (HTC), the conventional triaxial compression (CTC), and the constant mean pressure triaxial compression (CMPTC) tests were performed. The HTC test measured the volumetric response of the test powders under isostatic pressure from 0 to 13.79MPa, during which the three powders underwent a maximum volumetric strain of 40.8 per cent for Avicel® PH102, 30.5 per cent for A16SG, and 33.0 per cent for KY3500. The bulk modulus values increased 6.4-fold from 57 to 367MPa for Avicel® PH102, 3.7-fold from 174 to 637 MPa for A16SG, and 8.1-fold from 74 to 597MPa for KY3500, when the isotropic stress increased from 0.69 to 13.79 MPa. The CTC and CMPTC tests measured the shear response of the three powders. From 0.035 to 3.45MPa confining pressure, the shear modulus increased 28.7-fold from 1.6 to 45.9MPa for Avicel® PH102, 35-fold from 1.7 to 60.5MPa for A16SG, and 28.5-fold from 1.5 to 42.8MPa for KY3500. In addition, the failure stresses of the three powders increased from 0.129 to 4.41 MPa for Avicel® PH102, 0.082 to 3.62 MPa for A16SG, and 0.090 to 4.66MPa for KY3500, respectively, when consolidation pressure increased from 0.035 to 3.45MPa. In addition, the shear modulus and failure stress values determined from the CTC test at 2.07, 2.76, and 3.45MPa confining pressures are consistently greater than those from the CMPTC test at the same constant mean pressures. This observation demonstrates the influence of stress paths on material properties. The CTT is a useful tool for characterizing the three-dimensional response of powders and powder mixtures.

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