Study on the stress evolution law of surrounding rock and cooperative control technology in coal seam group mining

Aiming at addressing the challenges encountered in roadway support during coal seam group mining, this project focuses on the 212 main return-air cross-cut in Tucheng Mine, Guizhou Province. Through field investigation, numerical simulation, analog simulation, and field tests, the study reveals the stress evolution pattern of the 212 main return-air cross-cut and proposes the collaborative control technology of “unloading-rotating-fixing”. The findings indicate that the main cause of failure in the 212 main return-air cross-cut is the instability of the surrounding rock resulting from geomechanical issues during coal seam group mining. The floor and two sides of roadway produce different degree of stress concentration during mining. When the tunnel experiences vertical stress compression, the compressive force at the tunnel’s bottom is greater and the tensile force in the surrounding rock at the top is larger, leading to failure of the surrounding rock due to mechanical imbalance. Consequently, the “unloading-rotating-fixing” cooperative control technology is proposed. The shock waves generated by blasting induce vibration and stress fluctuations in the surrounding rock, dispersing the initially concentrated stress in the surface rock to deeper areas and reducing the stress concentration levels on the surface. Additionally, the surrounding rock around pressure relief holes is further reinforced using blasting and sealing techniques to form two load-bearing structures: the inner carrier composed of the roadway support system and the outer carrier formed by the deep surrounding rock. The interaction between these two components enables them to effectively withstand the stress from both shallow and deep surrounding rock of the roadway, transferring it to the supporting structure and playing a crucial role in protecting and stabilizing the surrounding rock. This technology was utilized during the field test at the 212 main return-air cross-cut with great success. The results demonstrate that the stress levels in the area tend to remain stable or even slightly decrease over time. The convergence speed of the roof, floor, and sides of the roadway is reduced by 74.49% and 47.67%, respectively, while the floor heave volume is decreased by 77.2%. However, in areas where this technique is not applied, the stress levels increase to varying degrees, leading to significant surface displacement convergence. It can be concluded that the control effect on surrounding rock is remarkable. This technology has been successfully implemented in other coal mines located in diverse geological environments in Guizhou Province, yielding remarkable outcomes.