Abstract: Taking the Yuheng mine in Northern Shaanxi as an example， aeolian-sand incipience experiment and water-sand inrush experiment were expansion by high-velocity seepage and entire visual equipment of water-sand two-phase flow. The experiment results indicated that， the loss of fine particles is the precondition of water-sand inrush and creates expansive space for the coarse particle migration. The process of water-sand inrush is a physical process， when the aeolian-sand size between 0.3~0.6mm， the energy transmits mainly in the form of particles collision.But it is different for the aeolian-sand size between 0.15~0.3mm， because the friction and squeeze are in the dominant role， that will lose less energy compared with collision. So the variation mass of aeolian-sand inrush is inversely proportional to the particle size. The critical velocity of aeolian-sand inrush is becoming higher with the increasing of axial stress. When the aeolian-sand begins to move， the seepage state is linear laminar flow and the critical velocity is 0.03~0.4cm/s for the aeolian-sand size d<0.6mm.The mass of sand inrush is proportional to the hydraulic gradient in unit time. It can be deduced from this result that water pressure of aquifer is the key factor， which greatly decisive the disaster degree of water-sand inrush.

Key words: thick unconsolidated formation, water-sand inrush, critical velocity, axial stress, drag force, volumetric expansion