Nonlinear seepage erosion model of water inrush considering particle size distribution of karst collapse column and its engineering applications

Water inrush through karst collapse column is one of the great disasters which threaten coal mine safety production. The particle size distribution of karst collapse column is one of its most basic physical properties, which has a strong correlation with particle migration, and is an important basis for evaluating the water inrush risk of collapse column. The nonlinear flow tests of broken rock under different gradation conditions were carried out by a custom-built apparatus, and the relationship equation between nonlinear flow parameters (permeability and non-Darcy factor) and Talbol power exponent n were constructed. A nonlinear flow model with variable mass of water inrush from karst collapse column was established. The spatio-temporal evolution law of pressure, velocity, porosity and concentration under particle loss and the influence of particle gradation on the water inrush risk of karst collapse column at Fan gezhuang mine were discussed. During the water inrush, the flow state of fluids in karst collapse column gradually transitions from a weak inertial flow to a strong one, eventually becoming a turbulent flow. The flow model based on single flow state cannot reflect the essence of flow regime transition in water inrush. The larger n is, the stronger the water permeability of the karst collapse column, the faster the particles migrate and are lost, the faster the flow channel with high porosity develops, the shorter the time for the water inflow to reach its peak value, and the greater the risk of water inrush.