黏结剂含量对含瓦斯煤剪切细观损伤力学特性影响的试验研究

Effect of binder content on mesoscopic damage mechanical characteristics of gas-bearing coal subjected to shear load

采用自主研发的含瓦斯煤岩细观剪切试验装置,开展不同黏结剂含量条件下的含瓦斯煤剪切试验研究,研究了煤的强度特性、裂纹演化模式、裂纹长度变化规律、细观裂纹形态特征和形成机制,并探讨了黏结剂含量对含瓦斯煤剪切力学特性、裂纹宏细观演化和损伤特性的影响。研究结果表明:随着黏结剂含量的增加,含瓦斯煤抗剪强度较好地服从线性增加关系,宏观裂纹的数目和分叉在增加,峰后稳定阶段所占总试验阶段的比例不断减小;裂纹总有效长度变化可分为急增、缓增和稳定3个阶段;随着黏结剂含量的增加,相邻裂纹之间的损伤区类型发生变化,宏观断裂面形成方式由裂纹的直接连通向主裂纹分叉连通和翼型主裂纹间损伤区连通方式转化;通过对黏结剂含量为5.3%条件下含瓦斯煤剪切细观裂纹形成机制分析可知,宏观裂纹前端存在几条由宽到窄、近似在一条线上分布的细观裂纹,前方新裂纹不断出现,后方裂纹不断长大,并发生翼裂纹连通,翼型裂纹重叠部分产生损伤,形成宏观裂纹,从而引起宏观裂纹不断向前扩展;主裂纹壁的次级裂纹是由几条呈雁行式排列的翼型裂纹组成;主裂纹之间的贯通方式为翼裂纹和反翼裂纹连通,取决于其相对位置。

In this study, shear tests are conducted on gas-containing coal with different binder contents using a self-developed meso-shear test equipment. Firstly, mechanical behaviors of coal are investigated, including strength characteristic, crack evolution mode, variation law of crack length, morphology and formation mechanism of mesoscopic crack. Then the effects of binder content on shear mechanical properties, crack macro-meso evolution and damage characteristics are discussed. The results show that shear strength of coal increases linearly with the increase of binder content, and the number and bifurcation of macroscopic cracks also increase, however the proportion of post-peak stable stage decreases. The development of total effective crack length can be divided into three stages： surge, slow increase and steady stage. With the increase of binder content, the type of damage zone between neighboring cracks changes and the mode of formed fracture surface converts from direct coalesces of cracks to bifurcation of main cracks and damage zone connection of the main wing cracks. The mechanism of formed shear mesoscopic crack of gas-containing coal with a binder content of 5.3% is analyzed. It is found that there are several mesoscopic cracks ahead a macroscopic crack, which changes from narrow to wide and approximately distribute along a straight line. Wing cracks connect, which are caused by the continuous appearance of new cracks in the front and the growth of original cracks in the rear. Once the overlap of wing cracks damages, a macroscopic crack occurs and then expands forward step by step. Secondary crack of the main crack wall is composed of several wing cracks arranged as an echelon. Coalescence modes of macro main cracks are connected by wing and anti-wing cracks, which depend on the relative position of adjacent cracks.