An Analog Model Study on Water–Sand Mixture Inrush Mechanisms During the Mining of Shallow Coal Seams

Water–sand mixture inrushes into shallow underground workings have caused casualties and property loss. A coupled fluid–solid analog model was developed to simulate the water–sand mixture inrush processes during mining from fracture production and development, based on the hydrogeological conditions at the #22304 working face of the Shigetai coal mine in the Erdos coal basin of northeast China. The deformation characteristics of the overlying strata and water pressure variations within the water-flowing fractured zone were monitored and analyzed. The results show that the water–sand mixture inrush consists of three stages: development of cracks in the overlying strata, initiation of a water inrush channel, and evolution of the inrush channel. The stresses of the overlying strata, water pressures, and permeability characteristics of water and sand inrush pathways change within the three stages. These findings lay a solid foundation for predicting water–sand mixture inrushes in shallow coal mines.