基于灰度共生矩阵和工业CT扫描的受载含瓦斯煤裂隙动态演化特征

Fracture dynamic evolution features of a coal-containing gas based on gray level co-occurrence matrix and industrial CT scanning

为研究受载含瓦斯煤在三轴压缩作用下的裂隙演化规律,利用受载含瓦斯煤显微工业CT扫描系统,开展了三轴加载条件下受载含瓦斯煤的工业CT扫描测试,获取了受载含瓦斯煤的应力-应变曲线和各变形阶段的CT扫描图形.运用图像分析软件对CT扫描数据进行了三维数字重建,实现了煤样内部裂隙的三维可视化和定量表征,并基于灰度共生矩阵(GLCM)理论分析了受载含瓦斯煤的裂隙动态扩展特征及规律.研究结果表明:瓦斯压力的存在一定程度上弱化了受载含瓦斯煤的力学性质,同时也加速了裂隙的扩展;受载含瓦斯煤二维裂隙先闭合后扩展,峰后快速扩展并形成连通二维裂隙网络;三维裂隙体积和裂隙密度呈现出先减小后增大的变化趋势,总体上可划分为裂隙压密闭合、新裂隙萌生扩展和主裂隙加速扩展贯通3个变化阶段;灰度共生矩阵分析中,对比度先减小后增大,能量和同质性先增大后减小,相关性呈现出单调递减趋势,准确描述了受载含瓦斯煤内部裂隙随应力增加不断变化的总体发展规律.

The expansion evolution law of internal fractures of coal under external load is of great significance to coalbed methane production and to control coal and gas outburst disasters.The coal body is in a three-dimensional(3D)stress state under the action of original in-situ stress.It is necessary to study the fracture evolution law of a loaded coal-containing gas under triaxial compression.The industrial computed tomographic(CT)scanning test of a loaded coal-containing gas under triaxial loading was carried out using the industrial micro-CT scanning system for the loaded coal-containing gas.The CT images and stress–strain curves of coal samples were obtained at each deformation stage.The 3D digital reconstruction of CT scanning data was carried out using image analysis software.Next,3D visualization and quantitative characterization of coal sample internal fractures were realized.Based on the gray level cooccurrence matrix(GLCM)theory,the fracture dynamic expansion characteristics and laws of the loaded coal-containing gas were analyzed.The results show that the existence of gas pressure weakens the mechanical properties of the loaded coal-containing gas and accelerates the expansion of cracks.The two-dimensional fractures of the loaded coal-containing gas first close and then expand,and then expand rapidly after the peak,forming a connected two-dimensional fracture network.The 3D fracture volume and fracture density first show a decreasing and then an increasing trend,which can be divided into three stages:fracture compaction and closure,new fracture initiation and expansion,and main fracture accelerated expansion and penetration.In the GLCM analysis,the contrast first decreases and then increases,the energy and homogeneity first increase and then decrease,and the correlation presents a monotonic decreasing trend.The analysis results accurately describe the overall development law of the internal cracks of the loaded coalcontaining gas changing with stress increase.