Analytical Solutions for a Single Vertical Drain with Vacuum and Time-Dependent Surcharge Preloading in Membrane and Membraneless Systems

Abstract

A system of vertical drains with combined vacuum and surcharge preloading is an effective method for promoting radial flow, which accelerates soil consolidation. This study presents the analytical solutions of vertical drains with vacuum preloading for membrane and membraneless systems under time-dependent surcharge preloading. Both vertical and horizontal drainage were considered in this analysis because they reflect realistic in situ conditions. According to the field and laboratory observations, the vacuum in the membraneless system was assumed to be decreasing along the drain; in the membrane system, it was maintained at a constant level. This model was verified by using the measured settlements and excess pore pressures obtained from large-scale laboratory testing and case histories in Australia, Korea, and China. The analytical solutions improved the accuracy of predicting the dissipation of pore water pressure and the associated settlement. The effect of the permeability of the sand blanket in a membrane system, and the possible loss of vacuum, were also discussed.