Bungle brings largest metro tunnel build to a grinding halt

Inadequate early investigations into the depth of building foundations in Parramatta have brought part of Sydney’s largest metro rail project to a grinding halt, threatening cost blowouts and delays.

For six weeks, two giant boring machines digging twin tunnels for the $25.3 billion Metro West line have been at a standstill several hundred metres east of the sprawling site in Parramatta’s CBD for a $380 million station.

The halt has been sparked by concerns about the depth of piles for one of the buildings that forms a major Telstra exchange, which extends for almost a block from Church to Marsden streets.

Two boring machines have been halted for weeks several hundred metres east of the site of a station (pictured) for Metro West in Parramatta’s CBD. Credit: Janie Barrett

Internal documents seen by the Herald show Sydney Metro and contractors were concerned, well over a year ago, about the prospect of one of the 180-metre-long tunnelling machines digging too close to the piles of the multi-storey Telstra building at 213 Church Street.

They show officials were still unsure last year of the depth of the foundations, and how close they were to Metro West’s planned northern tunnel.

Sources close to the project who requested anonymity due to the sensitivity of the matter say it raises questions about the failure to carry out adequate geotechnical investigations into the building’s foundations years before the tunnel alignment was chosen.

Some calculations have concluded the northern tunnel will come within four to five metres of the foundations. The capacity of piles to hold a building’s load can be undermined by the removal of underlying rock.

The documents show Sydney Metro and contractors have considered sending the tunnels deeper so as not to come too close to the piles.

However, the potential fix is complicated by the proximity of a giant hole for Parramatta’s underground station, and ongoing negotiations between Sydney Metro and contractors.

The project is at risk of further cost increases even if the tunnel is dug deeper – there are claims running into the hundreds of millions of dollars by Malaysian contractor Gamuda for delays to work as a result of the problems, sources say. Halting the boring machines has required a resequencing of work at the Parramatta station.

The Telstra building at 213 Church Street (behind the sandstone building in the foreground) is part of the telecom’s major telephone exchange in Parramatta.Credit: Edwina Pickles

Gamuda, which declined to comment, is leading a consortium that is building the nine-kilometre stretch of twin tunnels between Westmead and Sydney Olympic Park for the Metro West project. It is one of three major tunnelling contracts for the underground line, which will span 24 kilometres from Westmead to Sydney’s CBD once completed in 2032.

The estimated cost of tunnelling works at the line’s western end has already surged by $353 million from its original estimate to $2.7 billion, tender documents have shown.

Sydney Metro said it was aware of the matters relating to the Telstra building before awarding the western tunnelling package contract in 2022, and the contractors knew of them before starting work.

The agency said it was working with Gamuda and consortium partner Laing O’Rourke to finalise the design for the remainder of tunnelling and expected the boring machines to start again “very shortly”.

“Ongoing discussions between Sydney Metro and its contractors are commercial-in-confidence,” it said in a statement.

“Sydney Metro has been working with Telstra to co-ordinate geotechnical investigations at this site to verify ground conditions, foundations and pile depth of the building.”

The agency said geotechnical results had been used as input into the final metro tunnel design and alignment to “mitigate any risks to the buildings above”.

“Due to the complex function of the 213 Church  Street building, Sydney Metro has also completed investigations from an adjoining site to further verify foundation depths,” it said.

Inside one of the two 180-metre-long tunnel boring machines beneath Rosehill early this year.Credit: Nick Moir

Telstra said it was working closely with the government and Sydney Metro to ensure its infrastructure was not affected by the new metro station.

Transport Minister John Graham said it was appropriate that the tunnelling machines “proceed with an abundance of caution” as they neared the site. “Thankfully, we expect the [tunnel boring machines] to be back in action very soon,” he said.

Shadow transport minister Natalie Ward said Sydney could not afford for Metro West to lose momentum and be delayed a second time.

“However, taxpayers rightly deserve to know which expert signed off on the advice that has led to this issue,” she said.

Delays will create headaches for the government, which suffered a blow last month when Australian Turf Club members voted against selling Rosehill Gardens racecourse for $5 billion. The government had hoped to develop it into a new “mini-city” of 25,000 homes and build a metro station there.

Sydney Metro executives told a hearing in March that analysis provided to the government showed Metro West risks costing more than its $25.3 billion budget.

Start the day with a summary of the day’s most important and interesting stories, analysis and insights. Sign up for our Morning Edition newsletter.