On the morphology and pressure-filtration characteristics of filter cake formation: Insight from coupled CFD–DEM simulations

Abstract

The slurry filtration process at a tunnel face plays an important role in supporting pressure transmission, which is crucial to the stability of a tunnel face during shield tunneling. In this paper, a series of coupled computational fluid dynamics (CFD)–discrete element method (DEM) numerical simulations were carried out to model the slurry filtration column test. A simplified JKR (Johnson-Kendall-Roberts) model was used to simulate the cohesion between slurry particles. Four types of filter cake formation were identified under different combinations of size ratios between slurry and sand particles, and cohesion between slurry particles according to morphology and pore pressure distribution characteristics. These types were external filter cake, external & internal filter cake, internal filter cake & deep penetration and external & internal filter cake & deep penetration. The contact-based analysis of the constriction (void throat) sizes reveals that the dynamic evolution of the pore structure is closely related to the slurry infiltration process, i.e., the infiltration of slurry particles tends to seal the infiltration channel, which prevents infiltration of any more particles. The variation of Dc50 (the median constriction size) is closely related to the infiltration state of the slurry particles. The pressure drop within the filter cake becomes significant, i.e., the filter cake will become effective, only when the ratio of Dc50 to the size of slurry particles is below a threshold value. The current study provides new insight into the fundamental mechanism underlying the slurry filtration process during shield tunneling.