煤体成分及微结构与卸荷弹射相关性分析

Composition and microscopic structure of coal in relation to unloading ejection:a correlation analysis

选取内蒙古自治区鄂尔多斯煤田煤层(易弹射煤样,简称T⁃e)与山东菏泽煤田煤层(不易弹射煤样,简称T⁃d)进行对比分析,从煤的固有属性出发,开展真三轴压缩条件下高应力卸荷力学试验,分析煤的强度特征、破坏过程以及破坏断口的微观破裂特征与弹射程度差异相关性。结果表明:T⁃d中O含量少,Al含量高,细化晶粒,断裂及抗拉强度和冲击韧性显著增强,是影响弹射差异的成分因素;T⁃e内部存在明显的裂缝、层理结构等微结构,具有微结构发育、强骨架特征,是影响弹射差异的结构原因;煤固有属性的差异导致不同的力学显现,T⁃e峰值强度低、弹性模量较小,应变率大,在张拉和剪切应力相互作用下,宏⁃微观破坏呈现出复合破坏特征,破坏充分且剧烈,弹射明显;T⁃e的AE事件数及累积的能量剧烈增加,呈现3阶段特征,不稳定波动阶段表现为高能量释放。研究内容为探究煤体内在因素与卸荷弹射破坏相关性提供一种研究思路,为评价煤层冲击倾向性提供一种新的实验佐证,为针对性防治弹射提供一种防冲依据。

During the comparative evaluation,we selected coal seams(easy ejection coal samples,referred to as T⁃e)from Ordos coalfield in Inner Mongolia Autonomous Region,and coal seams(difficult ejection coal samples,referred to as T⁃d)from Heze coalfield in Shandong Province.Based on the inherent properties of coal,true triaxial compression tests under high⁃stress unloading condition were carried out.The strength characteristics and the failure process were analyzed,and the difference correlation between microscopic fracture characteristics at the rupture face and the ejection degree were also discussed.The results indicated that T⁃d had a low content of oxygen(O)and a high content of aluminum(Al).There was a significant enhancement of the refined grain,fracture and tensile strength,and noticeable impact toughness.The composition factors that affected the ejection difference were O and Al.In T⁃e,there were obvious microstructures such as cracks and bedding structures.These microstructures were characterized by extensive development and a strong skeleton pattern,and they were structural inducements that affected the ejection difference.Different mechanical behaviors were incurred due to the differences of inherent properties of coal,such as low T⁃e peak strength,low elastic modulus and large strain rate.Under the combined influence of tensile and shear stress,the sample displayed compound failure characteristics involving macro⁃micro failure,noticeable ejection,extensive and intense fracture.The acoustic emission(AE)events and accumulated energy of the T⁃e(tension⁃shear)increased sharply,exhibiting a three⁃stage pattern.Notably,the unstable fluctuation stage witnessed a high energy release.This research offers insights into the correlation between internal factors of coal and unloading ejection failure.Additionally,it presents a novel experimental demonstration for evaluating the impact tendency of a coal seam and establishes a foundation for targeted prevention and control of ejection.