Fractal Study on Mesodamage Evolution of Three-Dimensional Irregular Fissured Sandstone

In the present study, a numerical model was established to investigate the influence of the prefabricated cracks of different dimensions on the mechanical properties and damage evolution of irregular sandstone. To this end, prefabricated cracks of different dimensions were considered in the analysis, and the real mesoscopic structure inside the sandstone was characterized using microcomputed tomography (micro-CT) scanning and digital image processing technology. Combined with the rock failure process analysis system, the effects of the prefabricated cracks of different dimensions on its macroscopic mechanical behavior and damage evolution were studied. The irregular sandstone fissure field was extracted, the three-dimensional (3D) fissure field was visualized, and the corresponding damage degree was calculated on the MATLAB platform using the modified crack volume damage method. Based on the box dimension theory and the digital image storage principle, a 3D irregular rock fracture box dimension algorithm was developed. Moreover, the fractal dimension of irregular rock failure was calculated at the mesoscale, and the corresponding relationship between the fractal dimension of the crack region and the crack volume damage degree (Du) was established. The obtained results showed that the overall energy accumulation and internal failure of the specimen with nonpenetrating cracks have the characteristics of spatial-temporal inconsistency before reaching the elastic limit point, and the failure degree decreases along the fracture surface toward the intact surface. When the total volume of cracks was 1,800 mm3, the influence of crack parameters on the compressive strength of irregular sandstone was depth > length > opening width. It was found that the damage degree of irregular sandstone has a good consistency with the fractal dimension. This study helps to understand the failure mechanism of irregular rock particles and provides a new idea to investigate the damage evolution of irregular rock particles.