Abstract
Although a series of hypotheses have been proposed, the mechanism underlying coal and gas outburst remains unclear. Given the low-index outbursts encountered in mining practice, we attempt to explore this mechanism using a multiphysics coupling model considering the effects of coal strength and gas mass transfer on failure. Based on force analysis of coal ahead of the heading face, a risk identification index Cm and a critical criterion (Cm ≥ 1) of coal instability are proposed. According to this criterion, the driving force of an outburst consists of stress and gas pressure gradients along the heading direction of the roadway, whereas resistance depends on the shear and tensile strengths of the coal. The results show that outburst risk decreases slightly, followed by a rapid increase, with increasing vertical stress, whereas it decreases with increasing coal strength and increases with gas pressure monotonically. Using the response surface method, a coupled multi-factor model for the risk identification index is developed. The results indicate strong interactions among the controlling factors. Moreover, the critical values of the factors corresponding to outburst change depending on the environment of the coal seams, rather than being constants. As the buried depth of a coal seam increases, the critical values of gas pressure and coal strength decrease slightly, followed by a rapid increase. According to its controlling factors, outburst can be divided into stress-dominated, coal-strength-dominated, gas-pressure-dominated, and multi-factor compound types. Based on this classification, a classified control method is proposed to enable more targeted outburst prevention.
Highlights
Coal and gas outburst is a destructive disaster that occurs during underground mining, involving violent and spontaneous ejections of gas and coal-rock materials from the mining space (Ma et al 2020a, b; Guan et al 2009; Zou et al 2020; Wu et al 2020)
The results show that outburst risk decreases slightly, followed by a rapid increase, with increasing vertical stress, whereas it decreases with increasing coal strength and increases with gas pressure monotonically
We developed a multiphysics coupling model and a critical criterion for outburst
Summary
Coal and gas outburst (hereafter referred to as outburst) is a destructive disaster that occurs during underground mining, involving violent and spontaneous ejections of gas and coal-rock materials from the mining space (Ma et al 2020a, b; Guan et al 2009; Zou et al 2020; Wu et al 2020). A phenomenon of low-index outburst with increased mining depth has been observed; this refers to cases where an outburst occurs the seam had been identified as non-outburst prone based on current indices This phenomenon is difficult to prevent and can lead to serious loss. Fan et al (2017) suggested that outburst was caused by interactions among coal–gas media, the geology dynamic environment, and mining disturbance, and developed a stress-seepage-damage coupling model to simulate the evolution of the outburst dynamic system Based on this system, they proposed a formation criterion for the geological dynamic system, an instability criterion, and an energy criterion (Luo et al 2018). A mechanism of multiphysics-coupling-induced outburst is described and a classified control method is proposed
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