Force chains evolution and crack characteristics of multiple coal-rock sandwich composite structure by using particle flow code

The stability of residual coal pillars and surrounding rock structures in composite residual coal mining areas is crucial for the safe and efficient mining of residual coal resources. To explore the force chains evolution and crack propagation characteristics of multiple coal-rock sandwich composite structures, uniaxial compression tests with four types of multiple coal-rock sandwich composite structures were conducted using particle flow numerical simulations. The results showed that the characteristics of the force chain evolution and crack propagation characteristics of multiple coal-rock sandwich composite structures during the loading process were almost identical. The evolution of the internal contact force chains of the rock elements and the propagation of micro-cracks lagged relatively, induced mainly by the initial fracture of the coal elements. Moreover, the coal elements were instability hazard factors in multiple coal-rock sandwich composite structures. The energy released by the coal and rock elements affects each other, resulting in the destruction of the entire composite structure. This study provides a basis for the instability prevention and control of coal-rock bearing structures in composite residual coal mining areas.