Abstract: Water-sand inrush is one of the most common mine disasters in western China, which is adverse impact on safe-mining. This study aims to investigate the critical criterion of water-sand inrush occurrence and characteristics of water-sand migration. Water-sand transport experiments were conducted on four aeolian-sand samples with different particle sizes from an aquifer of Yuheng mine using high-velocity water-sand seepage equipment developed by the authors. The blended aeolian-sand was also measured using the aforementioned setup. Two critical velocities of water-sand inrush were identified. The first one is aeolian-sand incipience velocity ranging between 0.38?1.26 mm/s, and the second one is water-sand inrush critical flow rate with a range from 2.48 to 3.54 mm/s. The experimental data indicate that, one necessary condition of sand swarm startup is volume expansion. The process of water-sand inrush disaster is a physical process from quantitative changes to qualitative changes, which can be divided into three stages: 1) water brings sand, 2) water and sand get mixed and flow together and 3) sand brings water. The movement behavior of sand particles always manifest as concentration wave propagates. In this situation, the energy mainly transmits in the form of particle collision. When sand swarm starts, kinetic energy is transferred from water to sand. As the initial hydraulic gradient increases, the flow rate increases exponentially, and the amount of inrush-sand per unit time increases linearly.

Key words: water-sand inrush, critical velocity, sand bringing water, sand collision, particle swarm concentration wave