Experimental Research on the Mechanical Characteristics and the Failure Mechanism of Coal‐Rock Composite under Uniaxial Load

Abstract

Due to the influence of the component structure and combination modes, the mechanical characteristics and failure modes of the coal-rock composite show different characteristics from the monomer. In order to explore the effect of different coal-rock ratios on the deformation and the failure law of the combined sample, the RMT rock mechanics test system and acoustic emission real-time monitoring system are adopted to carry out uniaxial compression tests on coal, sandstone, and three kinds of combined samples. The evolution rules of the mechanical parameters of the combined samples, such as the uniaxial compressive strength, elastic modulus, and Poisson’s ratio, are obtained. The expansion and failure deformation characteristics of the combined sample are analyzed. Furthermore, the evolution laws of the fractal and acoustic emission signals are combined to reveal the crack propagation and failure mechanism of the combined samples. The results show that the compressive strength and elastic modulus of the combined sample increase with the decrease of the coal-rock ratios, and Poisson’s ratio decreases with the decrease of the coal-rock ratios. The strain softening weakens at the postpeak stage, which shows an apparent brittle failure. The combined sample of coal and sandstone has different degrees of damages under load. The coal is first damaged with a high degree of breakage, with obvious tensile failure. The acoustic emission energy value presents different stage characteristics with increasing load. Crackling sound occurs in the destroy section before the sample reaches the peak, along with small coal block ejection and the partial destruction. The energy value fluctuates violently, with the appearance of several peaks. At the postpeak stage, the coal samples expand rapidly with a loud crackling sound in the destroy section, and the energy value increases dramatically. The crack propagation induces the damage in the sandstone; when the energy reaches the limit value, the instantaneous release of elastic energy leads to the overall structural instability.

Failure energy evolution of coal-rock combination with different inclinations

“…Zhan et al [4] defined and derived the relative physical mechanical parameters of coalrock assemblages (CRCB) to illustrate and analyze the effects of coal-rock height ratio (CRHR), coalrock body behavior and interface parameters on the CRCB. Yang et al [5] conducted uniaxial compression tests on coal, sandstone and three composite specimens using the RMT rock mechanics test system and acoustic emission real-time monitoring system, combining the evolution laws of fractal and acoustic emission signals, and investigated the crack extension and damage mechanism of the composite specimens. Bao Pan et al [6] studied the deformation characteristics and loading damage laws of coal-rock assemblages under different coal-rock height ratios based on uniaxial loading and uniaxial cyclic loading tests.…”

Failure energy evolution of coal–rock combination with different inclinations

“…Zhan et al 4 defined and derived the relative physical and mechanical parameters of coal–rock combinations (CRCB) to analyze the effects of coal–rock height ratio (CRHR), coal–rock body behavior and interface parameters on the CRCB. By using the RMT rock mechanics test system and acoustic emission real-time monitoring system to combine the evolution laws of fractal and acoustic emission signals, Yang et al 5 conducted uniaxial compression tests on coal, sandstone, and three composite specimens and investigated the crack extension and damage mechanism of the composite specimens. Based on uniaxial loading and uniaxial cyclic loading tests, Bao Pan et al 6 studied the deformation characteristics and loading damage laws of coal–rock combinations under different coal–rock height ratios.…”

Investigation of the Bearing Characteristics of Bolts on a Coal–Rock Combined Anchor Body under Different Pull-Out Rates

“…Gong et al [28] found that there is a critical loading rate in the uniaxial compression mechanical test of the coal-rock combined body in the range of the low loading rate, and the coal-rock combined body has different mechanical properties in a certain range on both sides of the critical loading rate. Yang et al [29] concluded that, with the increase in the impact velocity, the maximum dynamic peak stress and peak strain of the coalrock combined body have an obvious strain rate effect, and the maximum dynamic peak stress increases as an approximate power function. Ma et al [30] found that the uniaxial compressive strength and elastic modulus of coal-rock combined specimens increase with the increase in the loading rate.…”