Numerical investigation of particle migration in fault zones during water and mud inrush using the CFD‒DEM approach

Abstract

Tunnels, mining activities and other underground engineering projects are frequently threatened by water and mud inrush accidents when they cross fault zones, which pose challenges to the safety and efficiency of underground engineering. The evolution of particle migration in fault zones under water seepage, which is the primary cause of water and mud inrush, is poorly understood. In this paper, the successive random addition method algorithm is used to generate fault surfaces with different Hurst exponents and employs CFD‒DEM coupled numerical simulation to study the evolution of particle migration and variable-mass seepage characteristics of fault fillings under different fault surface roughnesses and different fault spacings. The results show that a rough fault surface hinders particle migration. In variable-mass seepage through different rough fault surfaces, the loss of fine particles (d < 2.5 mm) exceeds 90%, and with increasing roughness, the contact force chains between skeleton particles decrease, whereas those between fine particles increase. The failure process of variable-mass seepage in rough fault fillings can be divided into three stages: particle migration and reorganization, particle clogging, and instability erosion of skeleton particles, whereas smooth faults (H ≥ 0.75) experience secondary development of particle loss. The expansion of fault spacing reduces the influence of rough fault walls on particle loss, but the rough wall still obstructs the flow of fine particles. These findings provide a scientific basis and technical support for studying and controlling water and mud inrush disasters in fault zones.