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

Abstract

During the past decade, the application of vacuum pressure for stabilising soft coastal clay and other low-lying estuarine soils has become increasingly popular in Australia, mainly due to the proven costeffectiveness in view of the significantly reduced time for achieving a high degree of consolidation and enhanced shear strength. Due to 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 (235ha) adjacent to the existing port facilities via land reclamation. A scheme of vacuum assisted surcharge load in conjunction with conventional surcharge and 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 pressure application. A comprehensive array of field data is presented to demonstrate how the embankment had performed during construction. A new 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 in the Port of Brisbane, for future design of port infrastructure under increasing live loads over the next two decades.