Simulation of non-spherical slurry particle re-infiltration dynamics in shield tunnelling using CFD–DEM

The slurry infiltration process and filter cake formation are widely studied due to their critical role in ensuring the stability of the excavation surface during slurry shield tunnelling operations. Previous studies have predominantly focused on static slurry infiltration through laboratory column tests and simulations. However, in real-world tunnelling, slurry infiltration is a dynamic process due to the forward movement of tunnel boring machines (TBM), where filter cakes are continuously disrupted and re-formed. In this paper, a numerical model simulating dynamic slurry re-infiltration during TBM advancement was developed using coupled computational fluid dynamics (CFD)–discrete element method (DEM) simulations. A total of 20 re-infiltration steps of slurry particle insertion, infiltration and cutter advancement were simulated and compared with static infiltration models. In the re-infiltration model, pressure fluctuations at the tunnel face seen in field measurements were reproduced, showing variations in pressure drop, void fraction, and permeability. As the sand particle size increased, more slurry particles infiltrated the internal and deep regions of each sand column, with fewer accumulating externally. Larger sand particle sizes led to more pronounced dynamic infiltration cycles and deeper particle infiltration. Additionally, the re-infiltration model demonstrated reduced infiltration compared to the static infiltration model at larger sand particle sizes, rendering the static infiltration model more conservative for coarse sands.