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Sydney Metro awards mega extension project 29 Jun 2017

Peter Kenyon, TunnelTalk

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.

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 (Fig 1).

Fig 1. Sydney Metro Southwest alignment and stations
Fig 1. Sydney Metro Southwest alignment and stations

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 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.

Fig 2. Sydney Harbour jet-grouting ground improvement works
Fig 2. Sydney Harbour jet-grouting ground improvement works

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.

Central Station upgrade shortlist
Sydney Central Station excavation works
Sydney Central Station excavation works

Three construction groups are shortlisted to complete the associated project-wide contract to upgrade Sydney’s Central mainline railway. In addition to cut-and-cover excavation of the metro platforms under the existing main line station platforms 12, 13 and 14, the project scope includes excavation of a 19m wide underground pedestrian walkway linking all the main line platforms and the metro line below.

The three shortlisted consortia are:

  • Laing O’Rourke Australia Construction
  • CPB Contractors/John Holland JV
  • Lendlease Engineering/Lendlease Building

The contract is expected to be awarded early next year (2018).

For the northern drives, assembly and commissioning of the two TBMs is scheduled to take place between mid-2018 with launch before end of 2018 and end of the drives by early-2020, a span of 12 to 18 months. For the southern drives, assembly and commissioning of the two TBMs is scheduled to take place between mid- and end 2018, with the drives expected for completion in mid-2020. All five machines are therefore expected to be in concurrent operation through 2019 and into early 2020.

New South Wales Transport and Infrastructure Minister Andrew Constance said: “This new metro line will eventually stretch 66km and connect dozens of suburbs along the way. When services through the city start in 2024, the tunnels will move more people than the Harbour Bridge and Sydney Harbour Tunnel highway connections combined.”

Once 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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