Abstract
In underground coal mining systems, the occurrences of coal burst hazards and pillar failures relate not only to the condition of stress distribution but also the geometry of roof-coal-floor structures. To study the failure response of these structures, the rock-coal-rock (RCR) sample, in which a coal component is sandwiched between rocks, is always employed as the experimental subject. In this study, the effect of height ratio (a ratio represents the height percentage of coal component in an RCR sample) on the mechanical properties and deformation behavior of RCR samples was numerically investigated by using the distinct element model (DEM). The results reveal the following. (1) The uniaxial compression strength (UCS) of the RCR sample decreases with increasing height ratio as an inverse proportional function. (2) With increasing height ratio, the elastic modulus of the RCR sample decreases exponentially, while the postpeak modulus is strengthened in an inverse proportional manner. (3) Microcracking activity of the RCR sample is different from that of the pure sample during loading. Specifically, a reactive period always occurs after the quiet and active periods in the RCR sample. (4) The RCR sample fails in a progressive manner, in which cracking bands develop preferentially in coal and then extend to rocks. Expectably, the mechanical properties and failure behavior of RCR samples are height ratio dependent, which may contribute to predicting the hazard of coal bursts and estimating the failure of rock-coal-floor structures.
Highlights
Coal bursts occur frequently in underground coal mining systems, causing fatal injury and facility damage [1,2,3].erein, coal pillar bursts refer to failures of roof-pillar-floor systems that have been a significant safety concern in deep coal mines (Figures 1(a-1) and 1(b-1)) [4,5,6,7]
The most height ratios were between 40% and 60%, and the results show the following. (1) e uniaxial compression strength (UCS) of the composite sample depends mostly on the coal component [12]
Two bonding behaviors are embodied in the contact-bond model (CBM) and parallelbond model (PBM) (Figures 2(a) and 2(b)) [30], both of which can be envisioned as a kind of glue joining two neighboring particles
Summary
Erein, coal pillar bursts refer to failures of roof-pillar-floor systems that have been a significant safety concern in deep coal mines (Figures 1(a-1) and 1(b-1)) [4,5,6,7]. Since coal seam is sandwiched between the roof and floor strata, the destruction of pillar is influenced by the condition of stress distribution and the geometry of roof and floor (Figures 1(a-2), 1(a-3), 1(b-2), and 1(b-3)) [8]. Erefore, understanding the mechanical properties and failure mechanisms of roof-pillar-floor structures under variable composite geometries is significantly important regarding safety mining. Coal seams and the surrounding strata may vary in thickness, which in turn indicates that the roof-pillar-floor structures may differ in physical geometry. The physical geometry refers to the height percentage (hr) of the coal component in a composite sample
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