CT可视化的受载煤体三维裂隙结构动态演化试验研究

Research on dynamic evolution of 3D fracture structure of loaded coal body based on CT visualization

为研究受载煤体中裂缝动态发展演化规律及其形态变化特征,以受载煤岩工业CT扫描系统为实验平台,开展单轴、三轴应力加载条件下煤样变形破坏全过程的工业显微CT扫描试验,得到能反映受载煤样失稳破坏全过程的三维裂隙结构CT扫描信息和应力-应变曲线等测试结果,运用VG Studio MAX图像分析软件,对CT扫描数据重建体模型得到的可视数字煤芯进行精准的裂缝提取和裂隙形态的数字化定性定量表征,对比分析了单轴、三轴受载条件下煤体裂隙发育形态的动态变化。研究结果表明:工业CT扫描是研究受载煤岩内部裂纹发育演化过程的有效手段,裂隙体积和裂隙率随应力的变化关系是受载煤样裂隙动态演化过程的直观体现,在煤样受载过程中呈现出缓慢降低-缓慢增加-急剧增加-增速放缓的发展规律;煤体在受载条件下内部裂隙演化经历了初始压密、弹性变形、新裂隙渐增、新生裂隙速增、裂隙扩展贯通和残余变形6个阶段,破坏形式为剪切破坏;煤样在三轴加载和单轴加载下的屈服强度和裂隙演化过程以及破坏后的裂隙形态均有显著差异,说明围压是影响受载煤体失稳破坏过程的重要因素;工业CT扫描图像显示,裂纹发育扩展随应力荷载的增加优先沿着矿物与煤基质的接触面开始起裂。研究结果可为煤炭合理安全高效开采及井下支护提供借鉴。

In order to study the dynamic evolution and morphological characteristics of fractures in loaded coal,the CT scanning system of the loaded coal-rock is used as an experimental platform to investigate the process of deformation and failure of coal samples under uniaxial and triaxial stress loading conditions.Micro-CT scanning test,the CT scan information and stress-strain curve of the three-dimensional fracture structure which can reflect the whole process of the instability of the loaded coal sample are obtained.The VG Studio MAX image analysis software is used to reconstruct the CT scan data.According to the numerical coal core for the precise crack extraction and digital qualitative and quantitative characterization of fracture morphology,the basic changes of coal fracture development under uniaxial and triaxial loading conditions are compared and analyzed.The results show that the industrial CT is an effective mean to study the internal evolution process of cracked coal and rock.The relationship between fracture volume and fracture rate with stress is a direct reflection of the dynamic evolution process of coal-bearing fissures.The fracture volume and the fracture rate show a slow decrease-a slow increase-a sharp increase-a slowing growth rate during the change of stress.The internal fracture evolution of the coal body under the loaded conditions is experienced six stages including initial compaction,elastic deformation,new crack growth,new crack growth,fracture expansion and residual deformation,and the failure mode is shear failure.The yield strength and fracture evolution process of coal samples under triaxial loading and uniaxial loading and the fracture morphology after failure are significantly different,indicating that confining pressure is an important factor affecting the failure process of loaded coal.Industrial CT scan images show that the crack growth is preferentially initiated with the increase of stress load along the contact surface of the mineral and coal matrix.The research results provide a reference for the rational and safe mining of coal and underground support.