Study on Characteristics of Acoustic Emission b Value of Coal Rock with Outburst-Proneness under Coupled Static and Dynamic Loads

Abstract

In this paper, a rock dynamic and static triaxial mechanical test system is adopted to conduct triaxial compression failure acoustic emission test on coal rock with outburst-proneness. The purpose is to study the evolution law of the acoustic emission (AE) b value of coal rock under static and dynamic load of varying frequencies. The test results show that the dynamic load disturbance will accelerate the instability failure process of coal rock, that the average stress level/ultimate strain of coal rock decline/rises correspondingly with the increasing dynamic load frequency. Moreover, the overall AE b value after dynamic load disturbance is relatively low, and the higher the dynamic load frequency, the larger the decrease in the b value. In addition, as the dynamic load frequency increases, the AE ringing count and AE energy show a trend of first increasing and then decreasing, and they are negatively correlated with the evolution characteristics of the acoustic emission b value. Furthermore, the change rule of AE b value is closely related to the instability and failure process of coal rock. A second-stage of the overall b value of acoustic emission shows a “cliff jumping type” decrease dip angle or “fault cliff type” decrease dip angle indicates the imminent failure of coal rock, which can be used as an evaluation index for real-time monitoring of dynamic disasters of coal rock with outburst-proneness.

Uniaxial Reloading Damage Characteristics of Critically Damaged Coal Samples at Different Confining Pressure Unloading Spans

“…Acoustic emission b-values (hereafter referred to as b-values) have previously been widely used in seismology and are commonly used to study the relationship between magnitude and frequency [26,27]. Commonly used ways to calculate the acoustic emission b-value are linear least squares, exponential least squares, and maximum likelihood estimation.…”

Study on the energy evolution mechanism of coal and rock with impact tendency under different strain rates

“…In addition, Zhang et al 6 also analyzed that the peak strength and elastic modulus of limestone increased sharply in the range of 5 × 10 –4 –5 × 10 –3 mm/s and decreased in the range of 5 × 10 –3 –5 × 10 –1 mm/s through uniaxial compression test of limestone. The damage of rock under different loading rates can be described not only by mechanical characteristics, but also by rock failure characteristics 7 – 10 , acoustic emission monitoring 11 , 12 , energy evolution characteristics 13 , 14 . Because the evolution law of internal energy of rock will directly reflect the damage and failure of rock under the influence of loading rate, the influence of different loading rates on rock damage and failure can be explained from the perspective of rock energy evolution.…”

“…loading rates can be described not only by mechanical characteristics, but also by rock failure characteristics [7][8][9][10] , acoustic emission monitoring 11,12 , energy evolution characteristics 13,14 . Because the evolution law of internal energy of rock will directly reflect the damage and failure of rock under the influence of loading rate, the influence of different loading rates on rock damage and failure can be explained from the perspective of rock energy evolution.…”