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Micro-CT-based temporal and spatial evolution of fractures and pores in loaded coal

YANG Qi;YU Yanbin;CHENG Weimin;ZHANG Xin;ZHENG Lei;CUI Wenting;XING Hao;State Key Laboratory of Mining Disaster Prevention and Control Co-founded by Shandong Province and the Ministry of Science and Technology,Shandong University of Science and Technology;College of Safety and Environmental Engineering,Shandong University of Science and Technology;China Coal Technology Engineering Group Chongqing Research Institute;  
As the main channel for fluid seepage,the fractured pores of coal have an important influence on the permeability of coal by their expansion and connection evolution laws under the action of mining stress. In order to reveal the evolution of the micro-fracture and pore structure characteristics of coal with axial stress loading,this paper used the NanoVoxel-3502E X-ray three-dimensional scanning imaging system and Deben loading test device to carry out the micro-CT in-situ scanning test of coal uniaxial compression. Acquired real-time CT data under different strain conditions,extracted the pores and fractures distribution characteristics of the coal sample,defined voidage and evenly divided the coal sample into three parts(region 1,region 2 and region 3) according to the stage of the voidage curve,and analyzed the evolution law of coal sample meso-structure with axial stress. The results show that that the uniaxial compression of coal presents staged fractures, and the distribution characteristics of fractures and pores are closely related to the internal stress propagation. The force transmission under uniaxial compression caused region 2 to appear first as the fractures and pores developed,followed by the development of region 1 near the axial stress loading indenter and connected fractures and pores,and at the peak(1 100 N) and after failure(492 N),the maximum volume and surface area of pores and fractures and voidage were the largest,while the fractures and pores of region 3 near the axial fixed indenter developed relatively slowly,and the maximum volume and surface area of pores and fractures and voidage were the smallest. The coal matrix(skeleton) was locally deformed and destroyed under the action of axial force,formed isolated pores and tiny fractures,and the spatial distribution of the fractures and pores aggravated the unevenness of the internal stress distribution in the coal,which in turn had a great impact on the process of coal rock fracture.
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