Composite Slurry Wall and Liner—A Full Scale Test

As part of the plan to increase the capacity of the Port of Brisbane, reclamation of a total area of 235 ha is in progress. The main geotechnical issue at the site is the extremely soft material dredged from the Brisbane River and Moreton Bay shipping channels. Over part of the reclamation area, Menard Bachy was selected by the Port of Brisbane Corporation to carry out deep soft ground consolidation, using the method of Vacuum Consolidation. In 2007, a trial area of 1.5 ha was first implemented. Following successful completion of the trial, a second and larger project was begun in 2009. The new single cell area of 9.3 ha is currently under vacuum depressurization and the soil consolidation is expected to be complete by early 2011. A significant feature in the vacuum system adopted is the 15m deep soil-bentonite cut-off wall incorporating a high-density polyethylene (HDPE) liner, which is required at the periphery, to isolate the vacuum areas over the depth of the permeable layers in the subsurface profile. To ensure the confinement required for the depressurization, the slurry wall and incorporated liner are joined to a surface cap HDPE liner to complete an air and water tight seal around and over the block of soil. The initial trial incorporating the deep cut-off wall was a first in Australia and was a success in terms of both outcome and execution with depressurization, under the vacuum membrane, being maintained constantly in the range of –0.80/–0.70 bars over a long period of time of 18 months. Confinement work on the current project, which is taking place over a significantly larger scale and using improved technique, is currently in progress. The ability of Soil-Bentonite slurry walls incorporating HDPE liners to perform as air-tight and water-tight barriers under high pressure differential (0.8 to 0.7 bars) and subjected to significant deformation has been tested on these large scale projects. The barrier system has proven to be effective for considerable periods of time.