Numerical investigation of variable-mass seepage mechanism of broken rock mass in faults

Abstract

The continuous migration and loss of small particles in fractured rock mass with water flow is the main cause of water inrush in fault zones. In this study, a fluid–solid coupling model for fault zone was established to study the complex coupling between the groundwater seepage and migration of broken rock mass, and reveal the mechanism of erosion-induced water inrush. The rock skeleton and broken rock mass in the fault zone were modelled by large skeleton particles and small filling particles, respectively, in 3D particle flow software while the fluid flow through the fault was modelled by the built-in computational fluid dynamics module. The numerical results show that: (1) with the increase of water pressure, the loss of filling particles increases continuously, and the whole seepage process can be divided into three stages: slow seepage, abrupt seepage and steady seepage, (2) the mass loss, porosity and permeability first increase slowly, then increase rapidly, and finally tend to be stable, (3) higher fine particle content are more likely to cause structural instability due to mass loss, thus increases the risk of water inrush and mud outburst.