煤矿覆岩破坏主要为弯载作用下发生的断裂，而煤岩介质的断裂特征对于冲击地压、煤与瓦斯突出等煤矿灾害密切相关。采用煤、泥岩、砂岩等不同介质的三点弯曲实验，研究了弯载作用下煤岩介质的强度特征、裂纹扩展规律、宏细观断口形貌特征及声发射变化特性，基于弹性断裂力学与均匀化方法对煤岩断裂机制进行了分析。研究结果表明：煤、泥岩样品的断裂峰值载荷、断裂能、断裂长度等断裂参数分布较离散，而砂岩样各参数分布则相对集中，该特征与煤岩介质内部结构密切相关，主要是由于煤及泥岩样品内部发育的微裂隙、微孔洞使得其均质度比砂岩样品高;宏观断口形貌方面，煤的宏观断口清晰可见原生裂隙，泥岩的宏观断口以微裂纹、微孔洞及层理为主，砂岩的宏观断口则仅包含少量杂质;细观断口形貌方面，煤的细观形貌表现为拉、剪断面和微裂隙，泥岩细观断口表面上分布有较多晶间断裂、微孔洞、黏土矿物及解理断裂，砂岩细观断口则仅为晶间断裂和少量微孔洞;煤样断裂声发射波形远比岩石要复杂，主波峰不明显，小断裂激发的声发射事件持续发生，而泥岩和砂岩的主断裂事件较显著，且在主断裂事件发生前通常有明显的起裂事件;弯载作用下煤岩介质尖端断裂扩展的临界应变能释放率主要受其弹性模量E控制，而介质的弹性模量与细观结构有关，且结构方向性对煤岩介质断裂特征具有重要影响。介质断裂的力学属性与宏细观断口特征之间具有密切的关系，对不同煤岩介质的断裂特征进行了初步的研究，认识到不同煤岩介质的细观结构对于其宏观断裂的重要影响，对于更科学严谨的结论，仍需要大量的实验数据支撑才能得以验证;煤岩介质的非均质性、各向异性使得其断裂机理十分复杂，探讨宏细观断裂的跨尺度问题、建立细观结构特性与宏观力学属性之间的内在联系，对于解决工程遇到的实际问题意义重大。

The fracture features of overlying rock,which usually cracks under bending load,have important effects on dynamic accidents such as rock burst.The three point bending experiments of different materials including coal,mudstone,sandstone were carried out to study the strength characteristics,crack propagation rules,macro and micro fracture morphology and acoustic emission variation of coal and rock under the bending load.Then the fracture mechanism of coal and rock was discussed based on elastic fracture mechanics and homogenization method.The results are shown as follows:① the distribution of coal and mudstone samples’ fracture parameters such as peak fracture load,fracture energy and fracture length are discrete,while the parameters of the sandstone samples are relatively close,which is closely related to the internal structure of coal and rock media.It is mainly the micro-cracks and micro-holes within coal and mudstone samples that make the homogeneity of them higher than that of sandstone samples.② As for the macroscopic of fracture surface,there are apparently primary fractures in coal,the micro-cracks,micro-holes and bedding in mudstone,and a small amount of impurities in sandstone.③ In terms of microscopic morphology,coal is characterized by tensile and shear sections and micro-fractures,and there are many inter-granular fractures,micro-pores,clay minerals and cleavage fractures on the surface of mudstone,while the inter-granular fractures are the main pattern in sandstone.④ The acoustic emission waveform of coal,whose main wave peak is not obvious,is far more complex than that of rock,with lots of AE events occurring persistently when rock cracks.In contrast,the main fracture events of mudstone and sandstone are very significant,usually along with obvious initiation events before the main fracture event.⑤ The critical strain energy release rate of the fracture extension at the tip of the coal and rock under flexural loading is mainly controlled by its elastic modulus E,which is related to the meso-structure and the structural orientation.This preliminarily study on the fracture features of different coal and rock media demonstrates that the fracture mechanics properties of different media have a close relationship with macro-mesoscopic fracture characteristics and the mesoscopic structure of different coal and rock medium have important influence on its macroscopic fracture.In addition,due to the heterogeneity and anisotropy of coal and rock media,the fracture mechanism of coal and rock is very complicated.It is of significance to solve the practical problems by the cross-scale argument about macro and micro fractures and the internal relationship between micro structure characteristics and macro mechanical properties.

1 实验方案

   1.1 试样制备

   1.2 加卸载方案

   1.3 监测方案

   1.4 加载路径

2 实验结果

   2.1 弯载作用下煤岩介质的强度特征

   2.2 弯载条件下煤岩断裂过程的裂纹扩展特征

   2.3 弯载破坏煤岩的断口宏细观形貌特征

   2.4 煤岩弯载断裂过程中的声信号特征

3 不同煤岩介质的断裂机制探讨

   3.1 煤岩介质断裂模型

   3.2 煤岩介质断裂机制分析

4 结论