Radial Filtration Model of Clogging Column for Prefabricated Vertical Drain Treatment of Slurry

In the prefabricated vertical drain (PVD) treatment of dredged slurry with high water content, fine slurry particles move toward the PVD membrane and accumulate around it due to the vacuum gradient. This process results in the formation of an almost impervious clogging column. The clogging column is cylindrical and symmetric about the vertical PVD axis, and it impedes vacuum consolidation of high water content slurry. A radial filtration model was created to describe the formation and growth of the clogging column using the equilibrium, continuity, kinematic, and constitutive equations in a cylindrical coordinate system. Essential components of the model are the moving boundary conditions for the clogging column–slurry interface and for the outer boundary surface of the slurry. The model accurately predicts temporal variation in the radius of the clogging column. Model predictions were compared to particle image velocimetry test results to validate the model. Real-time distributions of the void ratio, permeability, and effective stress for soil within the clogging column were also quantified and analyzed. The expansion of the clogging column was accompanied by compression of the soil skeleton. The distributions of the void ratio and permeability within the clogging column were highly nonlinear. The drainage rate of PVD was governed by the portion of the clogging column surrounding the PVD membrane.