Underground difficulties in Docklands and Southbank

As multi storey skyscrapers continue to change the Melbourne skyline from all angles, adding mass and depth to the glassy horizon, it is sometimes hard to imagine the land which Melbourne was built on all those years ago is predominantly comprised of reclaimed swamp land.

When it comes to building in areas such as Docklands and Southbank, engineers and construction workers regularly experience the presence of soft swampy soil.

Originally this region of inner Melbourne was low lying wetlands until it was reclaimed and then developed for the construction of light industries around Southbank and the Melbourne ports including Victoria Harbour in the area which is now Docklands.  

The soil attributes that make it difficult to build include:

• the presence of acid sulfate soil which is normally harmless when not exposed to oxygen (an aerobic environment), however should the acid sulfate soil be exposed to oxygen, a chemical reaction is initiated which produces sulfuric acid.
  • This acid has the ability to compromise the integrity of concrete, potentially undermining structural integrity and rendering it not fit for purpose in a structure;
• a shallow water table of approximately 1.5 metres below ground level;
• a lack of a solid geological foundation such as relatively accessible bedrock;
• highly variable ground conditions in the form of Coode Island Silts.

Thankfully engineers are a cluey bunch and have developed ways to ensure large structures which are eventually built in these areas do actually stay erect as intended and not become a leaning tower of Melbourne!

The main method structural engineers are able to ensure these towering structures remain upright in the challenging aforementioned soil conditions is by using a vibropiling drilling technique that allows for deep foundations. The steel piles are driven into the ground in situ using a vibrating mechanism to displace the soft soils and the remaining void is filled with concrete to form the foundation. It is important this technique is used so the exposure of acid sulfate soils to oxygen is minimised.  Similarly these types of deep foundations are only feasible when large design loads are built in these types of soil conditions. 

Naturally, with all of the above said, it would not make sense to excavate this type of soil for the development of underground carparking. It would just be too expensive to firstly shore up the excavation walls and de-water the pit but also the ongoing maintenance costs to keep the underground structure intact would be not economical in many ways.

Therefore for the majority of the residential and commercial buildings in Docklands and Southbank, above ground carparks have been incorporated into the design as it is much cheaper and easier to construct and maintain. This has lead to the design of some interesting architectural eye candy in particular Tower 5 at Yarra's Edge and the recently completed Concavo at Victoria Harbour. 

Another notable design in Southbank is the Eureka tower carpark which incorporated the Queen Bee art installation by local Melbourne artist Richard Stringer. The story goes Stringer developed the pieces, pictured below, as part of a studio series in 2003-2004 (coincidently when the construction of Eureka tower first broke ground).  

It is also said when Nonda Katsalidis viewed the studio exhibition, conversation ensued culminating in the unveiling of the art work in December 2007 on the tower's lower facade.

The Queen Bee sits at the top of a white box surrounded by a colony of worker bees. The symbolism of the art work refers to the gold mine workers during the gold rush and fits in with the design of the Eureka tower beautifully.

Future property developments located in Southbank and Docklands will continue to incorporate these structural principles when building in these areas - if anything it is an economic necessity. As far as carpark designs are concerned, some future proposals are incorporating vertical green walls to liven up the carpark facades which will definitely go some way in enhancing the city's visual urban experience. 

Sources and Further Reading

http://www.onlymelbourne.com.au/melbourne_details.php?id=15356

http://www.vibropile.com.au/