Performance and prediction of marine clay treated with vacuum and surcharge consolidation at port of Brisbane

Abstract

Over the past decade the application of vacuum preloading for stabilising soft offshore-coastal clay in shallow water and other low-lying estuarine soils has become popular in Australia. Its cost effectiveness is a major factor in most projects in view of the significantly reduced time for achieving a relatively high degree of consolidation. 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 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 layers of subsoil. The performance of a combined vacuum and surcharge fill system and construction of the embankment are described in this paper. A comparison of the performance of a combined vacuum and 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. This paper also evaluates the relative performance of the two contrasting preloading systems (i.e. vacuum and non-vacuum system). An analytical solution for radial consolidation that considers both time-dependent surcharge loading and vacuum pressure is proposed to predict the settlement and associated excess pore pressures of the soft Holocene clay deposits.