The specialist geotechnical engineering consultancy is joining forces with James Cook University and the Port of Brisbane as part of a three-year Australian Research Council industry-university linkage project. The project aims to make the dredging of shipping channels and ports more cost effective and environmentally friendly by finding new and more diverse commercial uses for dredged material.
Senior Principal of Coffey Geotechnics, Dr Jay Ameratunga, said the project was a significant one that will give other ports in Australia an opportunity to look at innovative ways of reclamation and development of their lands. It could lead to major improvements in the way ports managed dredged materials all over the world.
“The Port of Brisbane currently extracts around half a million cubic metres of dredged mud material every year and this has to be disposed of in some way,” he said.
“Our project is looking at ways to turn that poor quality material into useable engineering grade fill. This would mean that the Port could not only save on fill materials such as sand but also maximise the amount of dredged material that can be reused. This has obvious benefits for the environment and would make the entire dredging process more sustainable in the long term.
“Coffey Geotechnics will be providing direct financial support as well as two senior technical experts, myself and Professor John Atkinson, to offer in-kind support amounting to a value of $150,000 over the life of the project.
“There is also a keen interest from other Senior Principals within Coffey, including Ian Pedlar who has been involved in Port dredging work in Victoria over a long period, and Dr David Tonks from USA who has written several technical papers on dredged materials.”
Professor Siva Sivakugan, Head of Civil and Environmental Engineering at James Cook University said the research project would have two key components; laboratory studies and numerical modelling. Some of the numerical models will be verified against the ground improvement field trials conducted at the port.
“Part of the project will involve physical testing of samples and trying to figure out what the properties of the material are, how it behaves on its own, and how it behaves when you mix it with additives such as lime or cement,” he said.
“The main things we’ll be testing are the strength properties and the consolidation properties – how it behaves when settling. This will determine the possible uses of the material in an engineering context.
“We will also be doing numerical modelling so we can simulate the sedimentation process and predict the behaviour of the consolidated material.”
Technical issues with using dredged clays Unlike sands and gravels, clays and silts require stabilisation before they can be used as land reclamation fills or for other engineering purposes. However, dredged clays are difficult to handle and their performance under additional fill and live loads is uncertain. This means the reuse of dredged clay as land reclamation fill requires special attention and skill. Being young and rich in organic content, dredged clays are different to natural sedimented clays. Consequently, existing numerical models for these types of clays are not applicable to dredged clays. Dredged clay falls into two categories: ultra-soft and lumpy. Of these, firm lumpy clay is easier to handle but more difficult to characterize. Ultra-soft clay consists of fine clay minerals at high water content. Firm to stiff lumpy clay material on the other hand can be obtained from grab dredging in the firm clay layer. Ultra-soft clay: When subjected to additional fill load, ultra-soft clays undergo large settlements over a long period. Significant settlements occur during the early stage with minimal pore pressure dissipation. The settlement process may be faster if the material is placed in thin layers. Lumpy clay: Lumpy clay is normally placed in thin layers capped by a sand layer to enable primary consolidation to be completed within a reasonable time. However large settlement from such layers could be expected due to greater stresses at the top part of the foundation. Bo et al. (2001) stated that slight changes of geotechnical characteristics will be expected and that the settlement due to the close up of inter-lump void is minimal. It is likely that the addition of various substances such as lime and cement could result in significant improvements to the properties of dredged clay, rendering it suitable for a range of engineering purposes. |
Dr Ameratunga said the dredged material was essentially natural, unadulterated mud and was in plentiful supply. This meant it had great potential to become a useful resource rather than being treated as spoil.
“The dredged material has a high clay content so it’s not suitable for most engineering purposes because it retains air pockets and it takes a very long time to settle and compact,” he said.
“What this research intends to do is find a way to improve the quality of the soil to make it stiffer and make the settlement quicker so it can be used for purposes like clean landfill in land reclamation, and in paved roads.
“What we are doing isn’t new but it is innovative in the sense that we are finding a new application for an existing idea.”
Professor Siva Sivakugan said that if the project was successful, it would pave the way for more sustainable operations at ports around the world.
“We are hoping that our research findings will have application to many ports,” he said.
“At the moment we are focusing on Brisbane but Australia has major ports in Freemantle and Melbourne and elsewhere. We believe anything we do here can also be extended to other areas and even worldwide.”
Peter Boyle, Manager of Reclamation and Land Development at the Port of Brisbane Corporation, said the research had potential to revolutionise the way the Port managed its dredged material and make operations more sustainable.
“The Port of Brisbane Corporation is committed to finding ways of operating more sustainably, which means making economic progress, protecting the environment and being socially responsible,” he said.
“One of the biggest problems we face with dredging is that such a large amount of the mud material extracted is of a very poor quality. We currently use it as a low grade filler to reclaim land but we have to wait several years until it partially dries and then cover it with sand. The higher quality sand is dredged from the Moreton Bay shipping channels and provides a bridging layer across the dried surface of the mud.
“If we could improve the properties of the mud, we could use it as a high grade fill and we would require much less sand, which would obviously make our operation more efficient, whilst reducing the environmental impact. We might also be able to use it as a sub grade or as part of the pavement base layer so it’s possible we could use it for a range of purposes.”
Dr Ameratunga said this research would become more important as time went on because of the increasing pressure on port management authorities to operate sustainably. He said practical imperatives such as space and cost would also create greater motivation to act sustainably.
“Coffey Geotechnics has been involved in building a seawall at Brisbane to contain the dredged material and this was expected to have a lifespan of 20 years,” he said.
“It was completed in 2005 and it’s already almost a quarter full. Another disposal option is taking the material offshore and dumping it but this is a costly option and also has environmental issues because the silt takes so long to settle and impacts on underwater habitats.
“Our research project could have far-reaching implications for a range of operations. We expect that we can find ways to make land reclamation cheaper and more environmentally friendly by turning the dredged mud into a high grade material with multiple uses. This will result in a more sustainable outcome for all.”
The joint research project will commence in 2009.
For more information or to obtain high quality images, please contact Heather Potter at Mendleson Communication on + 61 3 9827 0422 or heather@mendleson.com.au.
Editor’s notes
High quality images are available on request.
Coffey Geotechnics is a subsidiary of listed company Coffey International Limited. Coffey Geotechnics is a consultancy providing specialist geotechnical engineering services in helping clients to manage the earth.
Coffey Geotechnics understands that earth materials such as soil, rock and water are the core foundations upon which social and physical infrastructure are built. We provide specialist knowledge from the early planning phase of investigation and analysis through to the design and construction of infrastructure.
Coffey Geotechnics is expanding rapidly around the globe. Currently, there are offices throughout Australia, New Zealand and the United Kingdom with over 700 employees.
The Australian Research Council linkage projects
The Linkage Projects scheme supports collaborative research and development projects between higher education organisations and other organisations, including within industry, to enable the application of advanced knowledge to problems. Typically, research projects funded under the scheme involve risk.
