Use of field trials to assess ground improvement at the port of Brisbane

A 235ha reclamation project is underway at the Port of Brisbane, which when developed is anticipated to accommodate expansion for port growth over the next 25 years. The reclamation site is underlain with weak and compressible deep Holocene clays, which will undergo significant settlements due to the development loads. The situation is exacerbated by the placement of reclamation materials, classified as clay or silt, commonly referred to as 'dredged mud' which are significantly weaker than the underlying Holocene clays. To improve the ground by the use of conventional surcharging techniques, would take up to 50 years or so to consolidate. The most economical technique identified is to use wick drains in combination with surcharging, to accelerate the consolidation process. In early 2006, it was decided by the Port of Brisbane Corporation to conduct large scale wick drain and vacuum trials to assess the effectiveness of the various techniques and to optimise designs before embarking on a full scale treatment of the reclamation site. The trials which commenced later in 2006 came to an end in December 2008 and provided valuable insight into and lessons about wick and vacuum treatment of reclaimed land. More importantly, the results of the trials have provided confidence in the future treatment work and optimised details such as the wick drain layout, type and quantities of wicks. The vacuum consolidation trial, applied to an area abutting the Moreton Bay Marine Park, also provided excellent results and highlighted the advantages of the use of the vacuum technique at boundaries of sites where instability is of concern.