Ground improvement trials
Client name: Port of Brisbane Corporation
Duration: 2006 - 2009
Location: Brisbane, Queensland, Australia
The project is the largest of its kind to be undertaken in Australia. Working closely with the client Coffey provided extensive local, specialist knowledge, innovative techniques and world best practice.
The reclamation area is underlain by extremely thick soft clays meaning significantly higher consolidation times and limiting surcharging options. In geotechnical terms these conditions are considered the worst for construction – but the Port of Brisbane needed the land.
The ground improvement method adopted was not without its challenges. Wick drains had never extended to such depths (greater than 35m) in Australia. Smearing during installation and possible kinking due to high settlements were all possible hurdles, plus the lack of local experience working with such high settlements (greater than 3m).
Adding to this was the large expense associated with trials involving such a wide area, requirement to test different types of wick drains plus the depth of soft clay.
Coffey worked closely with the client to identify and select the best solution, wick drains to depths up to 35m plus surcharging, to enable the post construction settlement to be reduced to the nominated criteria between 150mm and 250mm over 20 years. Wick drains to such a depth was an Australian first. By incorporating the trial area as part of the ultimate development the cost of the trial was neutral as it ultimately became part of the final project.
Coffey developed a program which incorporated the trials within the total development. By selecting an area which was not on a critical path for the port expansion the risk of reduced performance and therefore effects of delays were reduced.
Although the trial sites covered approximately 10.6 hectares and incurred a cost premium, they represented less than 4% of the area ultimately to be reclaimed and developed. Further, by incorporating the area as part of the development layout, the cost was anyway recovered.
These trials enabled the most significant ground improvements ever seen in Australia. They provided huge savings during the roll out and will continue to pay dividends to the Port Corporation by giving them confidence in their plans for further ground improvements.
Creating an Australian standard – When the trials were started, no international standard existed. A new European Standard for Vertical Drainage (EN 15237:2007) was only just being published. Standards Australia accepted a proposal by Port of Brisbane Corporation and Coffey to formulate a new vertical drainage standard based on the European Standard and learnings from these trials. After public consultation the Australian Standard 8700 titled “Execution of prefabricated vertical drains” was issued in 2011.
The work done on these trials have been disseminated to the industry by way of more than ten technical papers presented at national and international conferences. Given the importance of the work done The Port of Brisbane Corporation received a significant research and development tax benefit, from the Australian Government, based on the research work involved with the project.
Port of Brisbane Corporation and Coffey received the Innovation Award at the Institute of Engineers Australia (Qld Division) Excellence Awards in 2009.