Performance and Prediction of Vacuum Combined Surcharge Consolidation at Port of Brisbane

During the past decade, the application of vacuum preloading for stabilizing soft coastal clay and other low-lying estuarine soils has become popular in Australia. The cost-effectiveness is a major factor in most projects in view of the significantly reduced time for achieving a relatively high degree of consolidation. Resulting from an increase in trade activities at the Port of Brisbane, new facilities on Fisherman Islands at the mouth of the Brisbane River will be constructed on the new outer area (235 ha) adjacent to the existing port facilities through land reclamation. A vacuum-assisted surcharge load and conventional surcharge scheme in conjunction with prefabricated vertical drains was selected to reduce the required consolidation time through the deeper subsoil layers. The design of the combined vacuum and surcharge fill system and the construction of the embankment are described in this paper. A comparison of the performance of the vacuum combined surcharge loading system with a standard surcharge fill highlights the clear benefits of vacuum consolidation. Field monitoring data are presented to demonstrate how the embankment performed during construction. An analytical solution for radial consolidation considering both time-dependent surcharge loading and vacuum pressure is proposed to predict the settlements and associated excess pore pressures of the soft Holocene clay deposits.