IN A milestone week for underground tunnel projects in Perth, the Northbridge Link reached its first landmark with the launch of the tender process to sink the rail line, and the Graham Farmer Freeway turned ten.
IN A milestone week for underground tunnel projects in Perth, the Northbridge Link reached its first landmark with the launch of the tender process to sink the rail line, and the Graham Farmer Freeway turned ten.
Federal Transport Minister Anthony Albanese and state Transport Minister Simon O’Brien announced the tender launch last week to identify preferred contractors to sink the railway line.
Mr O'Brien said a contract could be let to a preferred contractor as early as February, with work physically commencing in the first quarter of 2011.
But Mr O’Brien said the cost for the project had bloated to $600 million, more than $100 million higher than the original estimate of $468 million, $236 million of which are federal government funds.
According to the state transport minister, neither the federal government nor the City of Perth would be expected to kick in any extra funds to finance the additional $100 million.
It is not yet known whether the tunnel to sink the railway will be constructed as a top down tunnel, as was the Graham Farmer Freeway, or as a bored tunnel, as was utilised for part of the Perth underground railway station.
It is also not yet clear how existing rail services will be disrupted during construction.
The top down, or cut and cover, construction method was used for the ten-year-old Northbridge Tunnel to minimise demolition of existing buildings.
Traditional tunnelling methods were not considered appropriate for the sandy ground conditions and high water table by joint venture participants Baulderstone and Clough.
The Graham Farmer Freeway cost $385 million to build, $230 million of which went towards the construction of the 1.6 kilometre tunnel.
The project was awarded the 2000 Institute of Engineers Australia engineering excellence award for infrastructure and building and also won the WA government C.Y. O’Connor award for engineering excellence.
The tunnel, which was opened to the public on April 24 2000, now carries more than 100,000 vehicles each day.
The other tunnel built in recent years in Perth’s CBD was part of the $1.4 billion Perth to Mandurah railway.
The tunnels, which were completed in October 2006, were undertaken by joint venture between Leighton Contractors and Japan-based Kumagai Gumai, which specialises in soft ground tunnelling.
Between 2004 and 2006, the Leighton Kumagai Joint Venture was affected by industrial disputes involving the Construction, Forestry, Mining and Energy Union.
A total of 107 workers were prosecuted by the Australian Building and Construction Commission for taking illegal industrial action over industrial safety at the site.
The tunnel’s cost, including track, overhead power and two underground stations, was $429 million, of which Leighton’s share was $236 million.
Part of the underground station required 600 metres of cut and cover tunnels and 700m of twin-bored tunnels, which were built under the water table.
Because of the soft ground in Perth’s CBD – a mixture of sand, clay and fine gravel – a specialised ‘earth pressure balance’ boring machine was required.
The boring machine was specifically designed for Perth CBD conditions by Japanese firm Mitsubishi Heavy Industries.
