A Dynamic Numerical Simulation on the Grouting Timing in Retained Rib of Pillarless Mining

A dynamic numerical method is established to simulate the stability of the surrounding rocks of the retained roadway in FLAC3D, along with a double-yield constitutive model to simulate the re-compaction process of gangue and a strain-softening constitutive model to simulate the strain-softening characteristic of the coal and the grouted fragmented coal after yielding. The simulation reveals that the grouting slurry diffusion range, the mining affecting the stage behind the working face and the retained coal rib deformation are closely interrelated. Under severe mining-induced stress, the integrity of the surrounding rock is more likely to be destroyed, accompanied by a large number of cracks developing and gradually expanding in the surrounding rocks. The roadway deformation increases in a rapid manner. Meanwhile, the grouting diffusing range increases gradually. The simulation conducted in this study indicates that the optimum support effect can be achieved by grouting in the section before and after the working face affected by the high mining-induced stress. A timely grouting can be used to construct an enhanced surrounding rock-bolting-grouting support system and maintain the stability of the retained roadway.