Piers that played a vital part in Sydney's development are being converted into highly desirable apartments.
In the shadow of Sydney's world famous harbour bridge and overlooking the spectacular Opera House, the most expensive real estate in Australia is taking shape.
The luxury apartments are central to the redevelopment of the Walsh Bay finger wharf, one of many built in the late 19th and early 20th century to provide extended length moorings for ships exporting agricultural products and wool around the world.
Proposals for the site also include the development of the central pier as an 800 hundredseater theatre for the Sydney Dance Company Redundant since the 1960s, the wharves have degraded.
Their timber piles suffered attack from marine organisms and termites while the ironbark decks and warehouses began to rot where water penetrated.
An attempt in the 1980s to knock down the wharves and extend the adjacent concrete loading facilities was finally averted when a redevelopment proposal from contractor Transfield and developer Mirvac was accepted. The agreement was signed in 1997 and in June 1999 an Act of Parliament granted the partners a 99 year lease on the property.
Walsh Bay used what were at the time innovative methods of driving and setting durable turpentine hardwood piles. On top large hardwood beams supported heavy timber decks carrying two and three storey warehouses.
However work on the new apartments has effectively required rebuilding of the pier structure. In view of the 99 year lease, all design has been based on a 100 year maintenance free design life, according to project consultant, Arup chief engineer John Ryder. 'After that there will be very limited maintenance required.'
Arup has been acting as engineering adviser for the project from the start, and has been responsible for all engineering aspects including condition surveys, detailed designs for the new and refurbished structures, and remediation design.
One of the first jobs was to reinforce the existing timber piles. In some cases it was possible to splice in new timber sections, but where whole piles had become unstable supplementary steel piles were driven adjacent.
A vigorous pile testing regime had to be put in place, as the complex is founded on soft sediments, and lying in an earthquake zone all Sydney's structures have to comply with strict earthquake codes. Testing confirmed that the piles were founded on the sandstone below.
Because of the site's industrial past, extensive remediation was needed. 'We had to comply with very strict codes, ' explains Mirvac development director Gavin Carrier. 'Most of the contaminated material was stripped and taken off site and new material bought in.' But the US$3.8M spend was relatively insignificant against the overall remediation cost, estimated at over US$154M.
Other measures to ensure there was no pollution of the harbour waters by construction materials included fitting all piers with collars to collect any overrun.
Another substantial cost has been architects fees, which Carrier estimates at 12% of the contract value. Main reason, he says, is down to the 'four or five redesigns' of the louvres on the balconies to meet the planning requirement that the building retained the warehouse style.
Further redesign was needed when the remains of what turned out to be Sydney's oldest cottage dating back to the 1820s was located. 'The archaeologists got very excited, ' jokes Carrier.
Negotiations with the authorities lasted over a year and the structures are now being built over the top of the remains.
The greatest engineering challenge for Arup proved to be a 400m 2underground car park facility which lies in the tidal zone. The concrete box was constructed with the deck slabs and formwork floated in and the lower slab jacked down off the upper slab. Temporary seals allowed completion in the dry.
The problem of getting materials on to a narrow, 200m long site, with water on three sides, has been solved by bringing in the highest freestanding tower crane in the southern hemisphere, which is anchored into bedrock in the dock alongside the wharf. Only 20m of the 60m tower stands out of the water.
Materials are lifted by the crane on to Australia's largest barge, anchored on the other side of the wharf, which is being used as a holding area.
There are no shortage of takers for the prime site. Even with penthouse flats costing in excess of US$3.3M, demand has been phenomenal. In the first 10 days of sales more than US$218M of real estate was snapped up.