After 17 months, Dorothy worms her way into giant hole for Parramatta metro station
A large tunnel-boring machine has finally arrived at a giant rectangular hole dug in central Parramatta for Sydney’s largest metro rail project after a delay caused by concerns over the depth of a building’s foundations.
The breakthrough completes a section of twin rail tunnels between Sydney Olympic Park and Parramatta, which will eventually form the $25.3 billion Metro West line.
The arrival of the machine, known as Dorothy, had been delayed by more than six weeks by fears about the depth of foundations for a Telstra building near the western end of the Parramatta metro station site.
A construction worker walks near the tunnel-boring machine named Dorothy.Credit: Sitthixay Ditthavong
Premier Chris Minns confirmed that the delay caused by concerns about the building’s foundations cost “some money”. He did not elaborate on the amount but said it was within contingencies for the mega-project.
“The truth of the matter is, when you’ve got a city as old as Sydney, and you are conducting difficult, complex engineering works, you are going to meet these challenges from time to time,” he said.
Once Dorothy restarts tunnelling westwards from the Parramatta station site, the 180-metre-long boring machine will dig slightly deeper to avoid foundations of the building at 213 Church Street.
The giant hole dug for the Parramatta metro station has numerous support beams due to the composition of the earth. Credit: Sitthixay Ditthavong
The other boring machine – Betty – arrived at the Parramatta station site early this month and, after a brief pause, has dug a further 175 metres westwards towards the last station on the line at Westmead, where a giant hole about 40 metres deep has been dug.
About 90 per cent of tunnelling for Metro West has been completed, and boring machines are due to reach either end of the planned 24-kilometre line by the end of the year.
At Parramatta, the giant hole – 196 metres long and 25 metres wide – for the station has required a significant number of large support beams because much of the earth comprises clay due to proximity to the Parramatta River.
Unlike stations under Pyrmont and the Sydney CBD for Metro West, the Parramatta station is a cut-and-cover site which involves digging a giant hole and later building over the top of it. Pyrmont and the Sydney CBD station sites involve excavating large caverns under city streets.
The giant rectangular hole for the station has been dug in the middle of the Parramatta CBD.Credit: Sitthixay Ditthavong
Sequencing of construction work has meant that the entire hole for the Parramatta station is yet to be dug to its full depth of 31 metres.
Once both boring machines have wormed further westwards, the rest of the hole will be dug to its full depth, which will involve demolishing some concrete tunnel segments left in their wake.
Since they started grinding through rock 17 months ago, the two giant boring machines have installed more than 48,000 precast concrete segments – each weighing up to four tonnes – to line the tunnel walls.
The Metro West line is due to open to passengers in 2032.
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