Thick and hard roof, Surrounding rock control, Combined blasting, Fragmentation and expansion support stress relief, Engineering geology. Rock mechanics. Soil mechanics. Underground construction, TA703-712

The deformation control of surrounding rock in gob−side roadway with thick and hard roof poses a significant challenge to the safety and efficiency of coal mining. To address this issue, a novel approach combining directional and non-directional blasting techniques, known as combined blasting, was proposed. This study focuses on the experimental investigation of the proposed method in the 122108 working face in Caojiatan Coal Mine as the engineering background. The initial phase of the study involves physical model experiments to reveal the underlying mechanisms of combined blasting for protecting gob-side roadway with thick and hard roof. The results demonstrate that this approach effectively accelerates the collapse of thick and hard roofs, enhances the fragmentation and expansion coefficient of gangue, facilitates the filling of the goaf with gangue, and provides support to the overlying strata, thus reducing the subsidence of the overlying strata above the goaf. Additionally, the method involves cutting the main roof into shorter beams to decrease the stress and disrupt stress transmission pathways. Subsequent numerical simulations were conducted to corroborate the findings of the physical model experiments, thus validating the accuracy of the experimental results. Furthermore, field engineering experiments were performed, affirming the efficacy of the combined blasting method in mitigating the deformation of surrounding rock and achieving the desired protection of the gob-side roadway.