As Sydney proceeds with new mega extension project of its Metro lines , the AUS 2.81 billion tunnels, stations and excavation contract for Stage 2 of the Sydney Metro is awarded to the John Holland (45%)/ CPB Contractors (45%)/ Ghella (10%) Joint Venture. At the same time, three groups are shortlisted to carry out upgrades to the city mail railway Central Station, with which the new metro line connects and passes under.

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The 15.5km-long all-underground Sydney Metro Southwest line, at a total cost of $12.5–13.5 billion, will extend the current Metro Northwest line (Stage 1) from its current terminus at Chatswood, through the city centre, to Sydenham (Stage 2). The new line includes a 750m-long twin running tunnel under Sydney Harbour.Tunneling work on twin train tracks under Sydney Harbour will begin within 18 months.

However the final cost of the tunnelling to provide Sydney with it’s second Harbour rail crossing and overall Metro rail line may increase because there are so many moving parts to the massive project.

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In addition to the main running tunnels on either side of the harbour, contract scope includes construction of:

  • TBM launch sites at either end of the alignment at Chatswood and Marrickville;
  • access shafts at each of the three mined stations at Victoria Cross, Martin Place and Pitt Street to facilitate excavation of the station caverns by roadheader;
  • three cut-and-cover stations at Crow’s Nest, Barangaroo and Waterloo;
  • a crossover cavern at Barangaroo;
  • a total of 57 cross passages on 240m intervals;
  • a temporary TBM reception shaft at Blues Point on the northern side of the harbour, to facilitate retrieval of the two TBMs that will complete the northern drives as well as the TBM that will complete the parallel drives under the harbour;
  • a grout batching plant and segment casting yard at the Marrickville site, plus storage for the 99,000 tunnel lining segments;
  • tunnel and station fit-out.

The new twin rail lines being bored beneath Sydney Harbour will form a crucial part of the planned $20.8 billion, 66km Metro rail route, running from the city’s northwest, through the CBD and down to Bankstown in the southwest.

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The John Holland/ CPB Contractors/ Ghella JV was selected over a rival bid from the Ferrovial/ Acciona/ BAM JV to win the contract.

The current excavation strategy requires the procurement of five TBMs, two be driven from the northern access site at Chatswood through to Blues Point temporary site on the north bank of the harbour, and two from the southern access structure at Marrickville that will drive through to Barangaroo Station on the southern side of the harbour (Fig 1). These are specified as double shield hard rock gripper machines, similar to the 6.99m diameter NFM machines that completed excavation in January 2016 of 15km of running tunnels through the Hawkesbury Sandstone geology of the central section of the 30km Metro Northwest alignment between Chatswood and Cudgegong Road. That project cost Aust$8.3 billion, with the underground works contract valued at $1.15 billion.

A hybrid machine capable of operating in both open mode and closed-face slurry mode will be procured for the twin 750m-long harbour crossing drives. According to the latest project schedule, this machine will launch following completion of cut-and-cover excavation of Barangaroo Station in early 2019 with a slurry separation plant established at the Barangaroo Station site to service the drives. Following a scheduled 6-9 month drive, the current design anticipated retrieval of the machine at Blues Point on the opposite side of the harbour for transport back to the launch site to complete the parallel drive.

To mitigate tunnelling risk, and prior to TBM launch, a program of ground improvement works will be carried out from barges on the harbour and at the locations where the geology transitions from Hawkesbury Sandstone to softer sedimentary layers (Fig 2). Ground improvement will limit the maximum operating pressure of the TBM through these transitions to 5 bar or less. Current design calls for establishing two grout blocks of 35m x 20m x 16m using the jet grouting process, although ground freezing may be preferred as the detailed design process takes shape.

nce the tunnelling drives are complete in 2021, work on the contract will continue along the 30km length of the project to lay tracks, fit out stations and upgrade the existing rail to metro rail services from Sydenham to Bankstown.

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Sydney Metro awards mega extension project

The Aust$2.81 billion tunnels, stations and excavation contract for Stage 2 of the Sydney Metro is awarded to the John Holland (45%)/ CPB Contractors (45%)/ Ghella (10%) Joint Venture. At the same time, three groups are shortlisted to carry out upgrades to the city mail railway Central Station, with which the new metro line connects and passes under.

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