Types and mechanism of water-sand inrush disaster in west coal mine

Water-sand inrush disaster is one of the most common problems in the shallow buried coal seam mining in western China region,and has adverse effect on mine safe production and fragile ecological environment. After analy- zing the types of water-sand inrush disaster in western coal mines,the influence mechanisms of porosity of porous me- dium,the particle sizes of broken rock mass and sand on water-sand inrush disaster are studied using self-developed porous medium two-phase water-sand flow testing system. The results show that water-sand inrush disaster can be di- vided into three types:cutting type,caving type and drilling induced type. The effect of porosity on water-sand inrush disaster has a close relation to the particle sizes of broken rock mass. The influence of porosity on pressure gradient and sand loss amount decreases with the particle sizes increase of broken rock mass. The sand loss amount increases with the increasing porosity and the possibility of water-sand inrush in low-porosity aquifer is less. At the same porosity and particle sizes of sand conditions,the smaller the particle sizes of gravels in aquifer,the higher the required pres- sure gradient for water-sand inrush disaster is,and the smaller the sand loss amount is. At the same porosity condition, the sand with 0． 074 -0． 25 mm diameter causes water-sand inrush disaster more easily than the sand with 0． 25-0． 83 mm diameter,and the smaller the particle sizes of sand is,the smaller the starting pressure of water-sand inrush disaster. At the same porosity condition,the sand loss amount increases nonlinearly with the particle sizes increase of broken rock mass.