Analysis of water and sand seepage characteristics in fracture

The permeability characteristics of water-sand in cracks or broken rocks are complex. The study on the seep- age characteristics of water-sand cracks is of great significance to reveal the mechanism of water inrush and sand rup- ture. Using a self-made instrument for water-sand fissure seepage test,the water-sand seepage test was carried out by changing sand particle size,concentration and other factors,and the hysteresis characteristics of water-sand flow in the fissure were obtained. Also,the hysteresis curve of velocity-pressure gradient of water and sand seepage in fractured rock was obtained from the test. A closed hysteresis curve of the seepage pressure gradient and the seepage velocity is formed in one cycle. With the increase of sand particle size and concentration,the curve changes from type I to type IV. The hysteresis parameters are described by the maximum hysteresis Gp and the hysteresis area S,both of whichshow an increasing trend with the increase of sand particle size and concentration,but the increase is not synchronous. Furthermore,the numerical simulation of water-sand fracture seepage field was carried out by using ANSYS Fluent software,and the variation rules of seepage field under the influence of different factors were obtained. Numerical simu- lation results show that the physical quantity of rough fracture flow field fluctuates with time. The flow of water and sand in rough cracks is restricted by the wall surface,which shows the randomness of the physical distribution of flow field. The simulation results show that the seepage field of water and sand is unstable,and the pressure loss of seepage field is inversely related to the particle size of sand. The average velocity and turbulent kinetic energy distribution of water-sand fluid on the fracture cross-section are greatly affected by the particle size and the concentration of the vol- ume of sand. This study can provide a reference for further study of water inrush from shallow coal seam.