Quantitative study on grouting plugging effect of loaded fractured coal sample based on CT scanning

The existing research on the fracture structure and grouting effect of grouting coal and rock mass cannot be quantitatively characterized. In order to solve the problem, the self-built grouting test system for loaded coal and rock mass is used to carry out the grouting test of different loaded fractured coal samples(uniaxial and splitting). The CT scanning of the fractured coal sample before and after grouting are carried out by using industrial CT scanning equipment. The image analysis software VG Studio MAX is used to accurately extract the fractures of the digital coal sample obtained from CT scanning data reconstruction model. The digital quantitative analysis of the three-dimensional fracture morphology and structure of the loaded fractured coal samples before and after grouting is carried out. ① The results show that the main fracture of the fractured coal sample under uniaxial loading penetrates from both sides of the top of the coal sample to the bottom of the coal sample and converges. The fracture width is basically unchanged. The coal sample is mainly fractured under the action of shear stress. The overall degree of fragmentation is large. The main fracture network is accompanied by more small fractures. The number of fracture above 50 mm is changed from 1 before grouting to 0 after grouting. The total fracture volume is reduced from 12 000 mm³ to 5 700 mm³ by 52.5%. It shows that the fracture structure of fractured coal sample under uniaxial loading is not conducive to slurry diffusion flow. The main fracture of splitting failure coal sample extends downward from the top to the middle and lower part of the coal sample along the vertical direction. The fracture width is large. And then the fracture tilts 45° to one side and continues to extend. The fracture width gradually narrows. The number of fractures above 50 mm is changed from 2 before grouting to 0 after grouting. The total fracture volume is reduced from 3 430 mm³ to 312 mm³ by 90.9%. It shows that the fracture structure of splitting failure coal sample is conducive to the flow and filling of slurry. ② The permeability of fractured coal sample under uniaxial loading is decreased from 57×10⁻¹⁴ m² before grouting to 1.2×10⁻¹⁴ m² after grouting by 97.9%. The permeability of splitting failure coal sample is decreased from 75×10⁻¹⁴ m² before grouting to 1.3×10⁻¹⁴ m² after grouting by 98.3%. It shows that grouting has a significant effect of plugging leakage and reducing seepage on coal sample with different failure forms. ③ The change of fracture volume and permeability of two kinds of coal samples before and after grouting are compared. It shows that although the grouting slurry of fractured coal sample under uniaxial loading only fills part of the fracture, the permeability difference is very small compared with the original coal sample. This result indicates that by blocking the connectivity of the air leakage channel, the fractures can be effectively blocked and a good grouting hole sealing effect is achieved. The research results can provide useful references for quantitative analysis of grouting in fractured coal and evaluation of grouting plugging effect in coal seam.