Hydraulic gradient effects on filter cake formation: microscopic insights from CFD–DEM simulations

• This study examines how hydraulic gradients affect the efficiency of filter cake formation using CFD–DEM simulations, • It explores the microscopic mechanism by which hydraulic gradients accelerate filter cake buildup, through CFD–DEM simulations of cone-shaped pore clogging, • The paper analyzes the variation of hydraulic gradients at different TBM cutter positions and their implications for filter cake formation, with reference to the Zhuhai Tunnel project. The hydraulic gradient strongly influences filter cake formation and plays a key role in maintaining tunnel face stability during slurry TBM excavation. To investigate this, a representative volume element (RVE) adjacent to a filter cake was modelled using CFD-DEM simulations, incorporating realistic sand particle sizes to reproduce filter cake development under varying hydraulic gradients. The study examines the effects of hydraulic gradients on impermeability, pressure drop, stress transmission, and the rate of filter cake formation. To further elucidate the mechanism by which a high hydraulic gradient accelerates cake buildup, a cone-shaped pore structure was analysed with coupled CFD–DEM. The results indicate that increasing hydraulic gradients enhance both the inflow rate of particles into soil pores and their velocity within the pores, thereby promoting rapid arching and accelerating filter cake formation. This work provides a microscopic perspective on slurry-induced pore clogging under different hydraulic gradients, with direct relevance to the excavation of the Zhuhai Tunnel.