加卸载应力作用下煤岩渗透率演化模型研究

Permeability evolution model of coal under loading and unloading stresses

为研究开采过程中煤岩力学行为及渗透率演化规律,运用含瓦斯煤热-流-固耦合渗流伺服试验系统,进行了不同加卸载条件下原煤力学及渗流试验,分析了加卸载应力作用对煤岩变形及渗流规律的影响,得到了剪胀角随塑性剪切应变的变化关系,发现了塑性剪切应变在1.6%左右会出现剪胀角急剧变化的现象。根据试验现象和结果,考虑煤岩结构对渗透率的影响,对煤岩在弹性阶段和屈服损伤后的结构进行简化,基于火柴棍模型及渗流理论分析,从应变的角度出发,探讨了加卸载应力对煤岩渗透率的影响,建立了两个不同阶段的渗透率模型(即弹性阶段和损伤阶段),基于不同阶段的渗透率模型和剪胀角规律,构建了煤岩全过程渗透率模型。所构建的渗透率模型与试验结果对比吻合效果较好,验证了该模型的适用性,可以为实现煤与瓦斯共采提供一定的理论依据。

In order to study the mechanical behavior and permeability evolution law of coal in mining process,the mechanical and seepage experiments on raw coal under different loading and unloading conditions were carried out by using self-made thermalhydro-mechanical(THM)coupling seepage servo testing system for gassy coal.The influence of loading and unloading stresses on coal deformation and seepage was analyzed and discussed.The relationship between dilatancy angle and plastic shear strain was obtained,and it was found that the dilatation angle changes sharply when the plastic shear strain is about 1.6%.According to the experimental phenomena and results,the structures of coal in elastic stage and yield damage stage were simplified by considering the influence of coal structure on permeability.Based on match stick model and seepage theory analysis,the influence of loading and unloading stresses on coal permeability was discussed from the perspective of strain,and two permeability models(i.e.in the elastic stage and damage stage)were established.Based on the permeability models in different stages and dilatancy angle law,the whole process of permeability model of coal was constructed.The permeability model constructed in this paper is in good agreement with the experimental results,which verifies the applicability of the expression and provides insights for the realization of coal and gas simultaneous extraction.