Physical modelling of consolidation of Hong Kong marine clay with prefabricated vertical drains

In this study, a small-scale physical model with full instrumentation was set up and used to measure the full consolidation process of a cylinder of clay with one prefabricated vertical drain (PVD) in its middle. The model test produced several interesting phenomena: (i) a delayed pore-water pressure increase under a constant pressure during loading stages, (ii) a delayed pore-water pressure decrease under a constant pressure during unloading stages, and (iii) residual excess pore-water pressures at the end of loading. Two analytical solutions accounting for the well resistance and a smear zone with reduced permeability are used to calculate the variation of average excess pore-water pressure with time, and these are compared with the measured variation. The well resistance of the PVD has a larger influence on the consolidation process than the permeability of the smear zone, especially during the latter stages of consolidation. The analytical solutions are able to show the influence of the well resistance of the PVD strip, but they cannot satisfactorily simulate the pattern of the residual excess pore-water pressure with time.