Journal
INTERNATIONAL JOURNAL OF COAL SCIENCE & TECHNOLOGY
Volume 10, Issue 1, Pages -Publisher
SPRINGERNATURE
DOI: 10.1007/s40789-023-00649-7
Keywords
CT scanning; Complex crack; Sampling threshold; Soft rock; Rock mechanics; Crack geometric parameters
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This study used CT scanning to extract the internal crack networks of coal specimens and statistically analyzed the relationship between crack geometric parameters and rock mechanics properties. The results showed that crack parameters were correlated with the uniaxial compressive strength and elasticity modulus of the specimens, and the internal crack structures of the specimens had an impact on their mechanical properties. For complex rock mass structures, it is recommended to analyze at least 16 cracks or geometric parameters with an area larger than 5mm².
Soft rocks, such as coal, are affected by sedimentary effects, and the surrounding rock mass of underground coal mines is generally soft and rich in joints and cracks. A clear and deep understanding of the relationship between crack geometric parameters and rock mechanics properties in cracked rock is greatly important to the design of engineering rock mass structures. In this study, computed tomography (CT) scanning was used to extract the internal crack network of coal specimens. Based on the crack size and dominant crack number, the parameters of crack area, volume, length, width, and angle were statistically analyzed by different sampling thresholds. In addition, the Pearson correlation coefficients between the crack parameters and uniaxial compression rock mechanics properties (uniaxial compressive strength UCS, elasticity modulus E) were calculated to quantitatively analyze the impact of each parameter. Furthermore, a method based on Pearson coefficients was used to grade the correlation between crack geometric parameters and rock mechanical properties to determine threshold values. The results indicated that the UCS and E of the specimens changed with the varied internal crack structures of the specimens, the crack parameters of area, volume, length and width all showed negative correlations with UCS and E, and the dominant crack played an important role both in weakening strength and stiffness. The crack parameters of the angle are all positively correlated with the UCS and E. More crack statistics can significantly improve the correlation between the parameters of the crack angle and the rock mechanics properties, and the statistics of the geometric parameters of at least 16 cracks or the area larger than 5 mm2 are suggested for the analysis of complex cracked rock masses or physical reproduction using 3D printing. The results are validated and further analyzed with triaxial tests. The findings of this study have important reference value for future research regarding the accurate and efficient selection of a few cracks with a significant influence on the rock mechanical properties of surrounding rock mass structures in coal engineering.
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