School of Architectural and Environmental Engineering, Zhengzhou University of Light Industry, Zhengzhou, Henan, China.
School of Safety Science and Engineering, Henan Polytechnic University, Jiaozuo, Henan, China.
PLoS One. 2019 Jul 18;14(7):e0219735. doi: 10.1371/journal.pone.0219735. eCollection 2019.
Coal and gas outburst is a common coal-rock dynamic disaster. Such accidents frequently occur, and the mechanism underlying the occurrence of these outbursts is complex. As a typical failure mode of a gas-filled and pressure-relieved coal body, the spallation mechanism should be investigated to reveal the mechanism of coal and gas outburst and guide outburst-prevention strategies. In this paper, a fluid-solid coupling model for coal seam gas flow is established. This model considers the adsorption characteristics of coal. Numerical calculations are used to simulate the stress field distribution and evolution of gas-filled coal bodies under different boundary conditions. The mechanical mechanism of the spallation occurrence after the pressure relief of coal is explained from the perspective of seepage breaking coal. The control of the flow and stress state of the gas to the spallation failure is analyzed. The mechanical-quantitative conditions for the initial failure of the coal body under seepage and the mechanical-qualitative conditions for the continuous advancement and termination of spallation are studied based on numerical solution results. The numerical calculation results show that the formation of a flow field after pressure relief will apply a drag force (tensile stress) on the porous media of coal. The presence of this force plays a crucial role in promoting the spallation and cracking of coal and, thus, the promotion of spallation. The tensile strength, initial adsorption pressure, and pressure relief rate of the coal body jointly control whether the initial failure can occur and the thickness of the fracture layer cracks. Spallation propulsion is mainly determined by the pressure relief conditions of the undestroyed coal body and pressure changes in the spallation space; the former can be quantitatively obtained by numerical calculations, whereas the latter is related to the thickness of the spalled layer and the degree of the layer-crack structure.
煤与瓦斯突出是一种常见的煤岩动力灾害，此类事故频繁发生，且其发生的机理较为复杂。作为含瓦斯卸压煤体的一种典型破坏模式，应当对其剥落机制进行研究，以揭示煤与瓦斯突出的机理，指导防突策略。本文建立了煤层瓦斯流动的流固耦合模型，该模型考虑了煤的吸附特性，采用数值计算模拟了不同边界条件下含瓦斯煤体的应力场分布与演化，从渗流破煤的角度解释了卸压后煤体剥落的发生机理，分析了瓦斯流动与应力状态对剥落破坏的控制作用。基于数值解结果，研究了渗流作用下煤体初始破坏的力学定量条件以及剥落连续推进和终止的力学定性条件。数值计算结果表明，卸压后形成的流场会对煤的多孔介质施加一个拖曳力（拉应力），该力的存在对促进煤的剥落和开裂、从而促进剥落起着关键作用。煤体的抗拉强度、初始吸附压力和卸压率共同控制着初始破坏能否发生以及裂缝层的厚度。剥落推进主要取决于未破坏煤体的卸压条件和剥落空间的压力变化，前者可通过数值计算定量得到，而后者与剥落层的厚度和层裂结构的程度有关。
