CFD-DEM modeling of seepage in foam-conditioned soil

Soil conditioning with foam agents can reduce the permeability of virgin soils and mitigate the risk of uncontrollable mud gushing during the excavation of Earth Pressure Balanced (EPB) shield machines. This study employs a combined Computational Fluid Dynamics (CFD) − Discrete Element Method model (DEM) method to simulate the seepage process in foam-conditioned excavated soil. Through discovering migration patterns of foam particles and their effects on macroscopic permeability under various hydraulic gradients, this study unveils the micro-mechanisms governing the permeability of foam-modified soil. Results indicate the feasibility of using hydraulic gradient amplification to examine foam particle migration channels and permeability changes. Furthermore, the findings show that the initial stabilization period in the seepage experiment arises from a dynamic equilibrium between the inflow and outflow of foam in the lower layers. In the upper and middle soil layers, foam migration paths show resilience to water pressure during the initial stage of seepage, but become increasingly responsive to the pressure when migration is hindered. The migration paths of the foam particles in the lower layers remain consistent across different water pressures. The migration speed of individual foam particles is determined by both water pressure and pore structure, while the overall migration speed of the foam increases as water pressure rises.