Abstract: A numerical model, called VRCS1, is developed for large-strain consolidation of saturated soft soil stabilized by PVD under vacuum-surcharge combined preloading. VRCS1 accounts for large strain, material nonlinearity, non-Darcian flow, vacuum loss along PVDs, and partial drain penetration. The estimated settlement using VRCS1 is in good agreement with field measurement for a site at Ballina bypass, Australia. Based on the field soil parameters, we investigated the effects of staged surcharge, cyclic surcharge, vacuum-surcharge combined preloading, equal stress/equal strain at the upper boundary, and PVD penetration depth on the consolidation of soft soil foundation stabilized with PVDs. The simulation results show that the staged surcharge can reduce the peak value of excess pore pressure and thus improve soil stability. The cyclic load produces oscillation during the consolidation process, and the peak value of settlement appears later than the peak values of excess pore pressure and load. There are fundamental differences between vacuum loading and surcharge loading, and vacuum loading cannot be simply replaced by surcharge loading. The consolidation rate under the condition of equal strain at the top boundary is generally faster than that under the condition of equal stress, and the real condition is usually between these two conditions. When the penetration depth of PVD exceeds 0.9 times the thickness of the soil layer, the effect of accelerating consolidation by increasing the penetration depth is weak.

Key words: saturated soft soil, prefabricated vertical drains, numerical model, large strain, parameter analysis