Evolution of mesoscale force chains at the structural steel-coal rock interface and macro-scale mechanical response characteristics

To elucidate the influence mechanism of coal powder moisture content on the evolution of mesoscopic force chains at the steel-coal rock interface under compression and the mechanical response of the structural steel surface, First, the surface morphology of structural steel and coal rock was reconstructed based on three-dimensional fractal theory. Simultaneously, integrating particle adhesion and fragmentation theories, a three-body contact model involving structural steel, coal powder, and coal rock was established. Subsequently, finite element-discrete element coupling (FEM-DEM) was employed for three-body contact simulation analysis. This approach investigated the evolution characteristics of the force chain network within the coal powder layer at the interface and the dynamic mechanical response properties at the interface.Finally, contact mechanical property tests were conducted to determine the contact mechanical parameters of the three-body system. Results indicate that under different moisture content conditions, external loads are first transmitted to the structural steel surface through the loading plane, then transferred to the coal-rock surface via mesoscopic force chains within the coal powder layer.The number of force chains in the coal powder bed exhibits a trend of increasing initially and then stabilizing over time. The length of force chains shows a trend of increasing initially, decreasing subsequently, and ultimately stabilizing over time. The moisture content (W) increased from 2% to 12%. The number of force chain particles in the coal powder layer exhibits an exponential decay relationship with the number of force chains, with the longest force chain comprising 11 particles. The evolution pattern of the mesoscale force chain network at the compressed structural steel-coal rock interface transitions from global force transmission dominated by long chains at low moisture content to local cooperative force transmission via short chain networks at high moisture content. The force chain structure’s capacity to transmit external loads gradually increases over time. At W = 2%, the structural steel surface exhibits the highest peak stress, which decreases rapidly over time. At W = 6%, the structural steel surface shows the lowest peak stress. The maximum deviation between simulation and experimental results for surface stress on the structural steel is 10.7%. The FEM-DEM coupled model for three-body contact between structural steel, coal power, and coal rock is effective and demonstrates high accuracy.