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.
Highlights
An increasing number of scholars have been studying the destruction mechanism and influencing factors of coal-rock composite structures based on experimental and theoretical approach. e experimental research is conducted based on the coal-rock composite with impact propensity, impact damage of electromagnetic radiation, and law of acoustoelectric effect [6,7,8,9]
Zhang et al [14] studied the influence of combination method on the mechanical characteristics and destruction characteristics of coalrock composite based on uniaxial and triaxial compression tests
Existing research mainly focuses on the mechanical characteristics and rock burst tendency of the combined sample based on experimental and numerical simulation methods, while the characterization of damage evolution during the loading procedure is analyzed with the help of acoustic and electrical signals
Summary
Erefore, the study on the stress characteristics and failure pattern of coal-rock composite is significant to prevent mine disaster. An increasing number of scholars have been studying the destruction mechanism and influencing factors of coal-rock composite structures based on experimental and theoretical approach. Qiu et al [12] studied the electromagnetic wave shape and spectral characteristics of coal and rock samples under uniaxial compression. Guo et al [15] analyzed the strength and macroscopic destruction mechanism of coal-rock composite with different dip angles based on numerical and experimental studies. Existing research mainly focuses on the mechanical characteristics and rock burst tendency of the combined sample based on experimental and numerical simulation methods, while the characterization of damage evolution during the loading procedure is analyzed with the help of acoustic and electrical signals. This paper can provide a theoretical basis for the prevention of mine engineering disaster and ensure safe and efficient mining process
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