Simulation study of top coal caving and conveying process based on smoothed particle hydrodynamics

Currently, in the numerical simulation research on the release laws of top coal during fully mechanized mining, complex coupling algorithms are required to address the continuity-discontinuity issues of top coal movement and ensure precise interaction of coal-rock interface information. However, the conveying process of scraper conveyors is typically neglected in these simulations. To address this problem, a meshless numerical computation model was constructed based on smoothed particle hydrodynamics (SPH). The discrete equations of SPH, derived from the control equations of continuous medium mechanics, were established. An elastic-plastic soil constitutive model along with the Drucker-Prager yield criterion were introduced to achieve dynamic simulation of the caving, movement, and release processes of the top coal. Considering the actual coal release and conveying processes in the mining area, a scraper conveyor model was constructed to simulate the release of top coal and the conveying of bottom coal along the working face, obtaining the variations in coal-rock interface and coal flow velocity at different scraper conveyor operating speeds (0-1.5 m/s). The simulation results indicated that the elastic-plastic soil constitutive model effectively simulated the flow behavior of particles. By setting parameters such as friction angle and elastic modulus, the issue of uncertain parameters commonly found in traditional discrete element models was avoided. After stabilization of the coal flow velocity, the stress distribution of the top coal near the coal drawing outlet exhibited a "double peak" pattern. The operating speed of the scraper conveyor significantly impacted the coal drawing time, while its effect on the coal-rock interface at termination and the shape of the released body was minimal. When multiple supports released coal simultaneously, the conveying capacity of the scraper conveyor needed to be considered, as interference in bottom coal transportation between different supports could lead to blockage effects at the release port. The "gangue closing" rule resulted in variations in the amount of coal drawing at different coal drawing outlets, with the standard deviation of top coal drawing amount from 40 coal drawing outlets (7.52 m²) being greater than that of automatic coal drawing (1.93 m²).