Soil behavior near the PVD filter and interpretation of clogging during vacuum preloading

Clogging near the prefabricated vertical drain filter during vacuum preloading reduces the efficiency of ground treatment, and existing research has yet to agree on the cause. This study conducted a small model test to comprehensively examine the soil’s water content and particle size distribution at different distances from the filter and tailwater for different preloading durations. The results showed that the particle size distribution of the soil at different selected points exhibited a slightly irregular difference. This indicates that no measurable migration of particles occurs, which was further confirmed by the particle size distribution of the soil after the one-dimensional consolidation test. The application of vacuum pressure did not significantly change the soil particle composition and, thus, its compressibility and permeability properties. The particle size distribution of tailwater revealed that a small number of fine particles with a mean size of 3–4 μm rapidly discharged with tailwater during the initial stage of vacuum preloading, which was much less than the mean size of the slurry and pore size of the filter. The decrease in water content and permeability indicates non-uniform consolidation, and the increase in the permeability coefficient ratio suggests the formation and development of the clogging zone.