Simulation Investigation On Water Sand Two Phase Transport Law In Rough Fracture

When mining coal seams in western mining areas,the overlying loose rock layers are prone to damage and form connected fractures,and the destabilization of water and sand mixture flowing in the fractures often leads to sudden water and sand inrush disasters.Therefore,the study of the transport law of water-sand two-phase flow in the fracture channel has become a basic topic for the prevention and control of water and sand inrush disasters.In view of the transport properties of the water-sand mixture in the fracture,the flow characteristics of the water-sand mixture in the single-alignment fracture channel,equal-opening rough fracture channel,and variable-opening rough fracture channel are studied using the coupled SPH-DEM method.The relationship between water-sand outburst amounts,water-sand outburst velocities and overburden pressure,fracture openness,and fracture roughness was analyzed.The main results are as follows:(1)Based on smoothed particle hydrodynamics theory(SPH)and discrete element theory(DEM),a coupled SPH-DEM model considering the action of lubrication forces was developed.The coupled model was verified by Poiseuille flow and spherical settlement rebound test in viscous solution.The SPH-DEM coupled model considering the action of lubrication force can accurately describe the interaction between fluid and moving solid,moving solid and fixed boundary,and fluid and boundary,thus accurately reflecting the transport characteristics of water and sand in the channel.(2)A water-sand outburst model was constructed under a single continuous fracture channel,and the effects of different boundary pressure,fracture opening width,and sand layer thickness on water-sand transport were analyzed by comparing the changes of cross-sectional flow and sand outburst rate with unit time.The results show that the cross-sectional flow rate and the maximum sand outburst rate are positively correlated with the upper pressure and the opening width,while they decrease monotonically with the increase of the sand layer thickness.Based on Bulsara's formula,the maximum mass flow rate per unit at different boundary pressures can be accurately described,which in turn reflects the degree of sand bursting.(3)The fractal function Weierstrass-Mandelbrot(W-M)with random parameters was used to construct the fracture roughness profile and establish the water-sand outburst model under the fracture channel with equal opening roughness.The variation law of water-sand transport under different boundary pressure and different fracture roughness was analyzed.The results show that the fractal dimension controls the roughness characteristics of the profile,and the random series affects the difference of the distribution position of the profile undulation.When the fracture roughness is the same,similar to the straight fracture results,the cross-sectional flow and maximum sand outburst rate are positively correlated with the upper pressure.While,when the roughness is larger,it plays a more obvious role in obstructing water-sand transport,and the retention of sand particles in the fracture is larger.(4)A model of water-sand bursting under the rough fracture channel with variable openness was built to analyze the variation law of cross-sectional flow rate and sand bursting rate under different boundary pressure and different fracture openness.The results show that the small opening section in the variable opening fracture is easy to cause the water-sand blockage at this place and reduce the flow rate of water-sand in the upper part of this section.And due to the persistent upper pressure,the larger the upper pressure is,the shorter the blockage time of a small open section,and the water-sand is more likely to get secondary acceleration.The variation of fracture opening in variable openness makes the water-sand flow state appear "completely blocked","semi-blocked" and "basically not blocked".Therefore,the change of opening in the fracture will cause the change of water-sand transport state,and the small opening area has a controlling effect on water-sand burst.There are 75 igures,14 tables and 108 references in dissertation...