Study on the macro and micro grouting process and the influence mechanism of cracks in soft coal seam

Abstract Grouting is an important method to reinforce soft coal roadway, and the presence of primary cracks in the coal body has an important influence on the grouting effect. Using the PFC (Particle Flow Code) method, the grouting process of the soft coal seam was simulated. The mechanism of primary cracks on grouting was revealed, while the influence of fracture characteristics and grouting pressure on the grouting effect was analyzed. The results demonstrated that grouting in the soft coal seam involved the stages of seepage, rapid splitting, slow splitting, and stability. Due to the presence of primary cracks, the grouting diffusion radius increased significantly. Under the slurry pressure, the tensile stress concentration was formed at the crack tip, and the slurry split the coal once the splitting pressure was reached. In addition, the distribution characteristics of fractures were found to have a great influence on the grouting effect. It was observed that smaller fracture spacing was associated with a larger slurry diffusion radius and thus easier penetration of the primary crack tips. The fracture angle affected the direction of fracture propagation. The secondary fracture formed by splitting was a tensile fracture, which was more likely to extend along the direction parallel to the maximum principal stress. Overall, these simulation results have guiding significance for the setting of reasonable spacing of grouting holes in the practice of grouting engineering.