摘要
温度变化对煤体损伤与破裂具有重要影响。温度变化导致非均质煤体内部产生热膨胀失配各向异性力,打破微裂纹临界受力平衡,引发煤体基质热开裂,继而导致煤体渗透率增大。从断裂力学理论出发,建立了煤体基质中单一微裂纹源热开裂的细观断裂力学模型,推导了微裂纹热开裂的临界裂纹尺寸,分析指出煤体温度变化越大,热开裂临界裂纹尺寸越小,即小裂纹越趋向于发育。引入微裂纹特征尺寸和孔径分形维数对煤体基质中单一微裂纹和空间裂纹网络进行表征,计算获得了煤体中微裂纹特征尺寸的分形维数,建立了煤体基质空间裂纹云的分形表征方法。以球形微孔为例,定义了热开裂增透因子,建立了基质热开裂增透力学模型,模型显示,随着煤体升温梯度增大,渗透率增透因子增大,基质渗透率增大效果越明显。最后对不同加热处理后的平顶山矿煤样和金佳矿煤样开展了压汞实验,加热温度分别为25,50,75和100℃,获得煤中微孔结构随温度的演化规律:煤体基质孔隙度随处理温度的增大而增大,孔径分形维数随处理温度线性增大,表明随着温度梯度的增大,煤体热开裂现象增强,基质渗透率增大。
Temperature variation has important influence on the damage and fracturing of coal block.When coal temperature changes,the anisotropic stress caused by thermal expansion brakes the critical stress balance of mi-cro-crack in coal matrix,leading to a thermal fracturing that increases the matrix permeability.In this paper,the thermal fracturing model of a single micro-pore source in coal matrix was established based on the fracture me-chanics,and the critical sizes of thermal fracturing induced pores in coal matrix were derived.The model shows that the larger temperature change corresponds to the smaller critical crack size,which indicates that the smaller crack tends to be developed.By introducing the fractal dimension of pore size and the characteristic size of micro-pore of the rock mass,a fractal characterization method to describe the spatial crack cloud in coal matrix was established.Taking a spherical micro-pore as an example,this paper defined a thermal fracturing caused permeability enhancement factor to establish the relationship between the thermal fracturing behavior of coal matrix and the permeability evolution.The research results show that the permeability enhancement factor increases with the increasing temperature gradient,which indicates that the permeability of coal matrix increases significantly.Finally,this paper carried out a series of mercury injection experiments with coal samples from Pingdingshan and Jinjia coal mines after different treatments under temperatures of 25,50,75 and 100 ℃,respectively.The experiment results show that the thermal fracturing and permeability enhancement enlarge with the increasing temperature gradient.
作者
滕腾
王伟
刘斌
郭俊廷
TENG Teng;WANG Wei;LIU Bin;GUO Junting(School of Energy and Mining Engineering,China University of Mining and Technology(Beijing),Beijing 100083,China;State Key Laboratory of Coal Resources and Safe Mining,China University of Mining and Technology(Beijing),Beijing 100083,China;State Key Laboratory of Water Resource Protection and Utilization in Coal Mining,Beijing 100011,China)
出处
《煤炭学报》
EI
CAS
CSCD
北大核心
2020年第2期676-683,共8页
Journal of China Coal Society
基金
国家自然科学基金资助项目(51874312)
煤炭开采水资源保护与利用国家重点实验室自主研发资助项目(GJNY-18-77)
关键词
热开裂
分形维数
增透因子
压汞实验
thermal fracturing
fractal dimension
permeability enhancement factor
mercury injection experiment
