Abstract
Rock burst is a catastrophic dynamic disaster caused by sudden failure and instability of coal, loading paths play an important role in the failure of coal, the coal failure process is associated with charge exception information. Hence, violent coal failure mechanics and time–frequency domain distribution of charge signal such as rock burst under different loading paths should be studied in-depth. In this paper, grade and cyclic loading test were carried out for coal with impact tendency samples produced by blocks cored from 800 depth in Xiaoqing coal mine of the Tiefa coal group in northeast China. Theory discussion was carried out for the result of stress and strain, frequency-spectra analysis was conducted for the wavelet charge data, figures showing the evolution mechanism of mechanical properties and the relationship of time–frequency domain amplitude of charge signals in coal with different loading paths and stage were obtained. The failure process and characteristics of coal under different loading paths were summarized. It found that the loading path changed the manner of energy accelerate–release, there were more plastic strain generation in coal under cyclic loading than that under grade loading, the former was more likely to cause greater damage and failure, then the strength of coal under cyclic loading is generally lower than that under grade loading, an energy conversion mechanical model of stress, damage and deformation was developed and explained the effect of the loading path. Charge signal was primarily distributed in the strengthening and peak stages, where there was a high amplitude pulse at each stress drop. The charge pulse was a type of low frequency signal with a primary frequency distribution range of 1 –100 Hz. Discussion on the charge generating mechanism from the perspective of friction slip, it demonstrated that the charge obtained during the coal failure process directly to stress loaded on and damage, the result verified it better. We propose that the research results in this study could be efficiently applied to daily mining activities, to provide an early warning and effectively avoid rock burst disaster.
Highlights
Rock burst is a dynamic disaster that causes spontaneous, violent fracture of coal in underground mines, which primarily occurs in roadways and working faces
The failure process and characteristics of coal under different loading paths were summarized. It found that the loading path changed the manner of energy accelerate–release, there were more plastic strain generation in coal under cyclic loading than that under grade loading, the former was more likely to cause greater damage and failure, the strength of coal under cyclic loading is generally lower than that under grade loading, an energy conversion mechanical model of stress, damage and deformation was developed and explained the effect of the loading path
Under cyclic loading, the first pulse emerged at the strengthening phase at approximately 51% strength, it worth notice that there was a high amplitude pulse at each point of loading turn to unloading, high amplitude signals are generated after loading in the strengthening phase, and the signal continuity is stronger than the grading load. It demonstrated the signal feature point waveform and spectrum, where the main frequency distribution primarily focuses on 1–100 Hz, and the amplitude of the main frequency band under grade loading was comparatively higher than that under cyclic loading. This result demonstrated that the loading path affected the mechanical properties of coal, further, it affected the During the coal failure process, the loading path changed the manner of energy accelerate–release, which was the reason that with different mechanical responses of coal for loading paths
Summary
Rock burst is a dynamic disaster that causes spontaneous, violent fracture of coal in underground mines, which primarily occurs in roadways and working faces. It can cause instantaneous failure of the coal mine and release elastic deformation energy spraying shattered coal into the mining space, inflicting injury and destroying equipment. Influence of external loading on the failure and deformation behaviors, induced by a mining stress field, become substantially evident and it causes the rock burst hazard evaluation to become considerably more difficult. Investigating the law of energy dissipation–release during the coal failure process, and the time–frequency distribution of charge signal, handing the relationship between them, using it to invert the stress and damage, to achieve the objective of early disaster warning and reduce disaster accident rates
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