Study on the migration law of water-sand mixed flow in porous medium based on erosion-seepage coupling in the fracture zone of sandy layer

This study aims to elucidate the spatiotemporal evolution mechanism underlying water-sand inrush phenomena within fractured sandy strata. An erosion-seepage coupling model tailored for fractured zones was formulated,incorporating nonDarcy seepage boundary conditions, rock matrix erosion dynamics, solid-phase mass conversion processes, and momentum transfer correlations. A comprehensive fully coupled framework was constructed,integrating a porous media water-sand seepage sub-model with a dynamic erosion sub-model specific to fractured sandy layers,culminating in the derivation of governing equations applicable to two -dimensional planar seepage scenarios. Based on COMSOL Multiphysics,the spatial and temporal domains are solved,and the results show that the difference in the sand content of the inflow phase and the pore-cavity mixed flow has a significant effect on the migration behavior of the water-sand mixed flow,and the larger the difference between the sand content of the inflow phase and the pore-cavity sand content,the more obvious the difference in seepage characteristics. The water-sand displacement process in the fracture zone of the sandy layer has experienced three stages: slow seepage, violent mixed-flow inrush,and steady-state laminar flow. The above model characteristics can be verified at the site of inclined shaft through sand layer engineering,and the practice of waterproof and sand control engineering is carried out.