Research on discrete element model and caving characteristics of fully-mechanized caving mining based on real coal gangue characteristics calibration

Fully mechanized caving mining technology is widely used in thick coal seam mining in China. The innovation of this technology needs to master accurate physical parameters and crushing parameters of coal caving and study its caving characteristics. In this study, the physical properties of coal and gangue were analyzed, and the density of coal and gangue, friction coefficient and recovery coefficient with Q345B steel plate were obtained. Using the three-dimensional structured light scanning reconstruction technology, the real three-dimensional feature model of 20 particles of coal and gangue is obtained, and the special-shaped coal gangue particle model is generated by profiling filling. By observing the collision and crushing phenomenon of coal gangue particles, combined with the comparative analysis of collision and crushing simulation and real crushing experiment, the optimal bonding parameters are determined. Based on the coupling of real coal gangue properties and discrete element simulation, a simulation model of coal caving is established. Combined with theory, experiment and simulation, the characteristics of coal caving are studied from macro, motion, mechanics and crushing. The results show that the maximum total vector force, total scalar force and total torque of gangue particles are 37.2%, 42.3% and 21.4% higher than those of coal particles respectively. The maximum total vector force, total scalar force, total torque and maximum pressure of the tail beam are 6.3%, 11.5%, 457.2% and 199.5% higher than those of the shield beam, respectively. The degree of particle breakage in the later stage of coal caving is 72.9% of the initial stage, and the crushing speed increases first and then decreases. There is a clear boundary between the moving and stationary parts in the top coal, and there is an approximately triangular low-speed zone above the shield beam. The study accurately determines the real coal gangue properties, systematically studies the coal drawing characteristics, and provides theoretical guidance for optimizing the fully mechanized caving mining process.