厚度效应对含瓦斯复合煤岩体力学特性及破坏形式的影响

On the impact of the thickness of the coal seam containing methane on the mechanical features and failure behaviors of composite samples

为了解厚度效应对复合煤岩体的影响,考虑了瓦斯及顶底部砂岩的作用,通过改变原煤与顶底部砂岩的厚度配比,运用含瓦斯煤热流固耦合三轴伺服渗流试验装置,研究了厚度效应对复合煤岩体的力学特性及破坏形式的影响。结果表明,复合煤岩体的三轴应力应变曲线与全煤样有很好的一致性,其三轴抗压强度较原煤有一定程度的增强;顶部砂岩与原煤厚度比落入1.00~1.20极值区间的复合煤岩体,易出现三轴抗压强度极值,且远离极值厚度比的三轴抗压强度均有不同程度下降;当厚度比接近1.00时,易出现峰值体积应变。当体积应变接近时,厚度比落入极值区间内的煤岩体强度较大。复合煤岩体的破坏以单斜面剪切破坏为主,且大部分为非完全破坏;中部原煤会产生多种形式的破坏,厚度比落入极值区间内的复合煤岩体,其煤体破坏以单斜面裂隙或垂直裂隙形式破坏,且三轴抗压强度要高于其他裂隙形式破坏。

This given paper is to study how the thickness of the coal seam may influence the composite coal and rock mass. For this pur- pose, we have taken into account the influential factors including the constitution of methane and sandstones at the top and bottom of com- posite coal seam and the rock mass. And, then, by changing the thickness ratio of the original coal seam and the sandstones at the top and bottom, we have made an exploration of the effects of the thick- ness On the mechanical properties and failure modes of the composite coal and the rock mass by means of a tri-axial stress thermal-hydro- mechanical coal structures including the methane permeameter. The results of our exploration indicate that the conventional triaxial stress- strain curve of the composite coal seam and rock mass used are well in accord with the curve of the coal bulk. The triaxial compressive stress of the composite coal seam and rock mass is likely to be a bit higher than that of coal bulk. If the ratio between the sandstone at the top of the coal seam and the raw coal seam drops to an extreme value interval of 1.00 to 1.20, the extreme value of the triaxial compressive stress is likely to arise more readily. What is more, the triaxial com- pressive strength tends to decrease at different heights if the ratios are higher or lower than their regular ones. If the thickness ratios are close to 1.00, their peak volume strain may tend to come about more easily. On the other hand, if the volumetric strains are closer, their stress may tend to be higher on the condition that the thickness ratios of composite coal seam and he rock mass fall into the mid level. Thus, it can be concluded that the composite coal and the rock mass prove to mainly suffer from the single shear failure, and most of them tend to suffer the incomplete damage. What is more, the raw coal seam in the middle may have a trend to generate different kinds of failure. For example, if the ratio of the thickness of the composite coal and rock mass comes to the extremely large or little one, the coal seams may turn to get damaged in the single shear crack or cracks in the vertical direction. And, if the triaxial compressive stress goes higher than the other kinds of cracks, the coal seam may turn to get damaged, too, though the crack manner may be different.