Abstract
Understanding the dynamic mechanical behaviors and microstructural properties of outburst-prone coal is significant for preventing coal and gas outbursts during underground mining. In this paper, the split Hopkinson pressure bar (SHPB) tests were completed to study the strength and micro-structures of outburst-prone coal subjected to compressive impact loading. Two suites of coals—outburst-prone and outburst-resistant—were selected as the experimental specimens. The characteristics of dynamic strength, failure processes, fragment distribution, and microstructure evolution were analyzed based on the obtained stress-strain curves, failed fragments, and scanning electron microscopy (SEM) and nuclear magnetic resonance (NMR) images. Results showed that the dynamic compressive strength inclined linearly with the applied strain rate approximately. The obtained dynamic stress-strain responses could be represented by a typical curve with stages of compression, linear elasticity, microcrack evolution, unstable crack propagation, and rapid rapture. When the loading rate was relatively low, fragments fell in tension. With an increase in loading rates, the fragments fell predominantly in shear. The equivalent particle size of coal fragments decreased with the applied strain rate. The Uniaxial compressive strength (UCS) of outburst-prone coal was smaller than that of resistant coal, resulting in its smaller equivalent particle size of coal fragments. Moreover, the impact loading accelerated the propagation of fractures within the specimen, which enhanced the connectivity within the porous coal. The outburst-prone coal with behaviors of low strength and sudden increase of permeability could easily initiate gas outbursts.
Highlights
Coal is an important source of fossil energy
The equivalent particle size of coal fragments decreased with the applied strain rate
A group of 14 coal specimens (Y1–Y14) from the Xintian coal mine were loaded to failure, with measured average strain rates varying from 17.18/s to 110.73/s; as a comparison, another group of seven coal specimens (X1–X7) from the Xinzhouyao coal mine were conducted, with the measured average strain rates varying from 22.76/s to 105.54/s
Summary
Coal and gas outburst usually occurs [1,2]. This dynamic disaster would suddenly eject a large amount of gases accompanying extensive coals [3], resulting in significant damage to equipment and may even cause fatalities [4]. The characteristics of short occurrence duration, high intensity, and strong damage made it scarcely possible to obtain geo-stress and gas pressure immediately, as well as to gain mechanical properties of coals under various impact loadings [12,13,14].
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