The purpose of the projects in Brisbane, Australia was to improve soft soils for a future expansion of the port facilities (Boyle, De Bok et al., 2007). Mud dredged from the harbour had been previously placed in large spoil areas inside containment dikes and allowed to dewater over time. Clayey deposits were still very soft after a period of several years of draining under their own weight. Moreover, the existing ground under the sea bed consists of soft compressible clay to significant depths (up to 45m). The projects are using a technology called Vacuum Consolidation to pre-consolidate the soils in advance of construction (Masse, Spaulding et al., 2001). Vacuum Consolidation is an evolution of conventional surcharge consolidation and also uses a pattern of vertical drains to accelerate the reduction in water content and thus force accelerated settlement of soft materials. Vacuum Consolidation requires that the block of soil treated to be completely confined so that atmospheric pressure can be used to increase stress within the material which in turn will induce its accelerated consolidation.
November 24, 2010 In Technical Papers