Abstract
The study of the energy accumulation and rate of release in hard coal under dynamic, static, and coupled dynamic-static loading and its failure mode is of significance when studying the mechanism underpinning coal mine dynamic disasters such as rock burst, coal, and gas outburst. In this paper, four experimental methods (uniaxial compression, Brazilian splitting, and coupled dynamic-static tensile and coupled dynamic-static compression) were used to analyze the energy accumulation, energy rate of release, and failure modes of this type of hard coal under different loading conditions. It was concluded that (1) the energy accumulation and rate of releases of this type of hard coal under static compression are 17.63–179.90 times and 18.57–13157.89 times those under static tension; the energy accumulation and rate of releases in dynamic compression are 2.11–248.53 and 0.23–48 times those under dynamic tension, respectively. (2) During dynamic loading, the ratio of compressive energy accumulation to tensile energy accumulation is reduced by 1.6 times compared with static loading, and the ratio of compressive energy release to tensile energy rate of release is decreased by 363.84 times compared with static loading. (3) The energy accumulation and rate of releases of this type of hard coal for dynamic tensile are, respectively, 2.64–17.42 and 1.07–5.26 times those under static tensile load; the energy accumulation under dynamic compression is greater than that under static compression, being 0.24–15.04 times that under static compressive, but the energy rate of release under dynamic compression is 0.0003–0.56 times that under static compression. (4) The greater the prepeak energy accumulation, the greater the degree of damage of the coal sample at each stage, and also the higher the degree of fragmentation after the failure. The research results play an important guiding role in further understanding the mechanism of coal mine dynamic disasters.
Highlights
With the increase in the scale of shallow coal mining, coal mining has gradually developed to a greater depth, and coal masses are more severely affected by high stress and mining disturbance, studying the energy accumulation and release and failure modes of coal under dynamic, static, and coupled dynamic-static loading is useful for revealing the mechanism underpinning coal mine dynamic disasters such as rock bursts [1, 2], roof falls [3, 4], and coal gas outbursts [5, 6]
Zhang et al considered the effects of depth on the in situ stress environment and physical properties of coal and conducted triaxial compression experiments on 128 coal samples that were on this basis, showing that, with increasing depth, the elastic energy and dissipated energy increase more rapidly [12]
Comparing the crack initiation and propagation process of the static (Figure 3) and dynamic (Figure 7) tensile samples, it is found that all the samples have cracks in the loading direction at the crack appearance stage, but dynamic tensile test specimens have a greater degree of crack initiation than samples under static tensile load
Summary
With the increase in the scale of shallow coal mining, coal mining has gradually developed to a greater depth, and coal masses are more severely affected by high stress and mining disturbance, studying the energy accumulation and release and failure modes of coal under dynamic, static, and coupled dynamic-static loading is useful for revealing the mechanism underpinning coal mine dynamic disasters such as rock bursts [1, 2], roof falls [3, 4], and coal gas outbursts [5, 6]. Hao et al used the stress-strain curve of the uniaxial compressive test to establish a new bursting liability evaluation index for coal [10]. Liu et al made research on the damage evolution mechanism of the overall creep failure process of coal rock under uniaxial and triaxial compression load [20]. Aiming at the failure mode of coal, the research focuses on the initiation and development of cracks in the failure stage of coal and the description of its behavior after failure: few have studied the energy accumulation and release of coal under different loading conditions and different failure modes. Rough the analysis of the stress-strain curve and failure mode, the energy storage in, and release from, the coal body under different loading conditions were obtained. Four experimental methods (uniaxial compression, Brazilian splitting, dynamic tension, and dynamic compression under coupled dynamic-static loading) were adopted to study the mechanical properties of coal under different load regimes. rough the analysis of the stress-strain curve and failure mode, the energy storage in, and release from, the coal body under different loading conditions were obtained. e analysis of coal failure modes under different loading conditions is of significance to the prevention and control of coal mine dynamic disasters
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