1. Department of Mechanics and Science Engineering,Liaoning Technical University,Fuxin　 123000,China; 2. School of Civil Engineering,Hebei University of Science and Technology,Shijiazhuang　 050018,China

煤体是具有孔隙、裂隙结构的固体介质,孔隙的贯通程度、裂隙的宽度是煤层渗透能力的重要指标,为了使煤体裂隙结构发生损伤而达到增透的目的,对三轴受载煤样进行注液氮冷加载实验,利用液氮注入钻孔煤实验装置系统对煤样施加4 MPa围压,分别进行多周期冷加载作用,通过高倍相机、金相显微镜、声波测速仪和CT成像系统观测煤样表面裂隙宽度、波速衰减率及内部结构损伤情况。根据单轴压缩实验的应力-应变曲线,分析煤样结构随冷加载周期的变化规律。结果表明:(1)煤样裂隙结构损伤程度随冷加载周期的增加而增大,损伤速率随注液氮周期的增加呈现先增加后降低的非线性变化规律;(2)煤样经6周期注液氮冷加载后表面发生颗粒脱落,经过7周期注液氮冷加载后发生宏观碎裂;(3)冷加载对煤样原生裂隙损伤效果显著,并沿着层理方向延伸。液氮冷加载能使煤体结构发生显著损伤,这为冲击地压灾害防治与瓦斯治理提供了新的方法。

Coal is a solid medium in which contains pore and fissure structure. The extent of interconnection of pores and the width of the cracks play important roles in the permeability of coal samples. To fracture the coal and enhance its permeability,the cooling loading experiment of the coal samples under triaxial compression through liquid nitrogen injection was performed. The test equipment of liquid nitrogen injection into drilled coal samples was developed. The confining pressure of 4 MPa and several periods cooling loading were executed,respectively. The high magnification camera,metallurgic microscopy,sound wave velometer tester and CT imaging system were employed to investigate the evolution of the surface crack width,wave velocity and inner damage structure. According to the uniaxial compression stress-strain curve,the inner micro-structural change law of coal samples with cooling loading periods was studied. The results show that:① With the increasing periods of the cooling loading,the damage becomes much more serious. The damage velocity increases firstly,then decreases. So it is nonlinear. ② Particles drop off from the surface of coal sam- ples after 6 periods cooling loading,and the macroscopic fragmentation appears after a 7 periods cooling loading. ③ The damage and fracturing effects of liquid nitrogen cooling loading are much more remarkable for the initial fissures,and the expansion of the cracks mainly extends along the bedding direction. Liquid nitrogen cooling loading can evi- dently damage and fracture coal bed,and is a new method to prevent from rock and gas outburst.

国家自然科学基金资助项目(51704142；51474121；51574139)；

LI Hewan,WANG Laigui,ZHANG Hao,et al. Investigation on damage laws of loading coal samples under cyclic cooling treatment[ J]. Journal of China Coal Society,2017,42(9):2345-2352.