Pre-cast concrete modules were the answer when WA’s biggest building infrastructure project needed a series of huge stormwater detention basins to keep its surrounding areas lush and green.

 

By Brian McCormack

When the $2 billion Fiona Stanley Hospital opens in Perth next year, not only will it be WA’s biggest-ever building, but also a testament to sustainability.

Already the winner of a United Nations environmental award, the hospital will showcase numerous water sensitive urban design measures, implemented to improve the efficiency of water-use within the hospital, as well as the management of stormwater quality and quantity.

The hospital occupies a 32-hectare site with more than five hectares of bushland, landscaped parks, internal gardens, courtyards and plazas. All stormwater will be retained on-site to sustain these green areas, along with off-site programs, including investment in community-based conservation efforts.

To meet the stormwater management objectives, main contractors Brookfield Multiplex specified five underground stormwater detention and infiltration systems, and a stormwater harvesting system. Humes won the contract to supply the detention basins on the basis of their unique pre-cast StormTrap modules, which could be delivered to the site at the rate of 30 units per day and hoisted into place with relative ease. 

The project engineers then identified an opportunity to replace a large retaining wall and detention basin with a sixth StormTrap system. The StormTrap system was as cost effective as building the retaining wall, while also providing the additional advantage of moving the detention basin below ground and freeing up land for other purposes. 

This was the largest detention system supplied for the project, with a storage capacity of 3708m³. Its design included a grated side opening to allow extension and interaction of the basin with nearby vegetated bushland during a high-flow event – a further example of the client’s focus on delivering a water sensitive urban design solution.

With a tight building schedule and a requirement for early completion of the civil drainage works, the StormTrap system was an ideal fit for the project. Humes delivered approximately 30 units of the stormwater system to site each day. Each piece took approximately 10 minutes to install, with each of the systems completed and ready to be backfilled in less than 10 days. This quick installation allowed the civil and structural works on buildings, roads and car parks to progress without delay. 

Designed in accordance with AS 5100.2-2004 – Bridge Design Code, the StormTrap system provided a fully trafficable solution for the project, enabling flexibility in terms of where the system could be placed in the hospital grounds. It also enabled the managing contractor to maximise the site for traffic and storage during construction, even before the surface was completed.

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