Slurry TBM makes five on Sydney Metro 12 Sep 2019

All five TBMs are now underground and at work excavating the 15.5km City and Southwest extension to the Sydney Metro. Supplied by Herrenknecht, the five machines include four double-shield TBMs, as well as a Mixshield TBM for excavation under Sydney Harbour, a route that will require boring through a section of Harbour sediment. The specialised machine was the last to begin work, departing from its Barangaroo launch site on the south side of the Harbour in early August 2019.

Slurry TBM arrives

In addition to the twin tunnels, the new Metro line includes six new underground stations: Crows Nest and Victoria Cross to the north of the Harbour, and Barangaroo, Martin Place, Pitt Street, and Waterloo to the south (Fig 1). The tunnels, stations and excavations works package for the project was won by a John Holland-CPB Contractors-Ghella JV in June 2017 at a contract value of AUD$2.8 billion. The contract also includes a launch portal at Marrickville and a temporary TBM retrieval shaft at Blues Point. Bechtel is the Delivery Management Partner for the client, Sydney Metro.

Under a separate contract, Sydney Central Station - located between the new stations at Pitt Street and Waterloo - will be extended underground in a AUD$955 million works package awarded to Laing O’Rourke in March 2018. The AUD$1.3 billion M&E contract for the entire line was awarded to the Systems Connect JV of CPB Contractors and UGL.

Progress of excavations

The first TBMs for the running tunnels launched in late 2018 to excavate the 8.1km section between Marrickville and Barangaroo in the south of the city and on a route that will take them under the central business district. Both have now broken through at Pitt Street Station, a distance of about 6km, after launching in October and November 2018 and boring at a rate of 128m/week and 136m/week, respectively.

Mixshield barged back to Barangaroo for twin Harbour drive

On 30 October, history was made when the first TBM drive at up to 40m beneath sea level under Sydney Harbour, completed breakthrough at the Blues Point Station site on the north shore. The Herrenknecht Mixshield took about 16 weeks to complete the 1km drive after launch in June from the Barangaroo Station site on the south side and averaging about 55m/week. The machine is now back at the Barangaroo site for reassembly and relaunch on its second under harbour crossing. Also completing its drive, and the first of the five Herrenknecht TBMs on the project to achieve final breakthrough, is the double shield machine that excavated one of the 6.2km running tunnels south from the new station at Crows Nest, through the Victoria Cross Station site, to the Blues Point station on the north side of the harbour.

To the north of the Harbour, two TBMs are excavating a 6.2km alignment between Chatswood and Blues Point. The first of these machines launched in January 2019, breaking through at the end of a 4.5km drive at the site of the new Victoria Cross Station in late August, after excavating at a rate of 125m/week. After a three week maintenance break at Victoria Cross, it will relaunch to bore the final 1.7km section of the alignment to the edge of Sydney Harbour, where it will be retrieved from a temporary shaft at Blues Point. The second TBM was launched in mid-February 2019 and has bored about 4km at a rate of 124m/week. It is expected to breakthrough at Victoria Cross in September 2019.

The twin 6m i.d. segmentally lined running tunnels will be connected with cross-passages at 240m intervals.

Under Sydney Harbour, the Hawkesbury sandstone drops below the alignment, requiring the TBM to excavate through sediment deposits. The Environmental Impact Assessment (EIS) originally indicated a multi-mode machine would be required for the drive, however, after extensive additional geotechnical investigation, using a remote-operated vehicle and carried out by the contractor, a slurry-type TBM was specified and a Herrenknecht Mixshield was procured for the project. This additional ground investigation also eliminated the need for additional ground treatment of the transition zones between the sandstone and sediment deposits from barges anchored in the Harbour, which had been anticipated in the EIS.

Fig 1. New line adds 15.5km to Sydney Metro

The Mixshield was launched from the working site in Barangaroo in June 2019. During advance under the harbour, the machine has encountered more clay than expected, reducing advance rates to about 29m/week. At the end of the excavation, it will be retrieved from the Blues Point site and returned for relaunch from Barangaroo to complete the twin drive under the Harbour.

The underground stations are being constructed using both cut-and-cover, at Crows Nest and Waterloo, and drill+blast, at Victoria Cross, Barangaroo, Martin Place, and Pitt Street. The underground extension at Sydney Central Station is also using cut-and-cover construction (Table 1).

The cavern at Victoria Cross is 40% larger than any other station on the Sydney Metro, measuring 270m x 25m x 20m. Three roadheaders were used to construct the cavern, excavating 360,000t of rock. The 228 x 23m x 16m Barangaroo Station is about 88% complete with work underway to secure the ground. In the crossover rail cavern, steelwork, waterproofing and concrete pouring have begun. The Martin Place Station cavern is also almost complete and will measure 220m x 12.4m x 15m. The Pitt Street Station comprises two 247m x 14m caverns set 84m apart. A concrete pile retaining structure was built before excavation of the station shaft areas to support the ground during excavation. Three roadheaders have excavated the station caverns and pedestrian connections.

Of the cut-and-cover stations, the 202m x 24m-26m x 33m Crows Nest Station took 15 months to excavate with large piling rigs and rock bolters installing 225 piles around the edge of the station box to support the ground during construction. Waterloo Station took 12 months to excavate the 200m x 25m x 26m box. Ground anchors and sprayed concrete supported the concrete pile retaining structure during excavation, which was begun by surface miner down to 30m below to the surface.

Central Station

At Central Station, and in addition to new Sydney Metro platforms, the construction contract package includes an underground 19m wide concourse to connect passengers entering from Chalmers Street to suburban rail and Metro platforms and to new light rail and bus services. The Northern Concourse will also be upgraded with new pedestrian thoroughfares and a feature roof.

“The upgrade to Central Station represents the biggest improvement to the station in decades,” a Sydney Metro spokesperson told TunnelTalk. “It will make it easier for customers to connect between light rail, suburban and inter-city trains, the Sydney Metro, and buses.”

Construction of the underground metro platforms began in 2018 and is expected to be complete in late 2022. On completion of the Central Station contract, track will be laid along the 30km of the City and Southwest lines and stations fitted out before the start of services in 2024.

“Work to build the metro platforms is happening while Sydney train services continue to run through the rest of Central Station,” the spokesperson continued. “As work happens around them, more than 250,000 customers continue to access train services in Australia’s busiest railway station.”

Sydney Metro development

The City and Southwest extension is Stage 2 in the development of the Sydney Metro, following the opening of the Stage 1 Northwest route this year. The two Metro sections will link at Chatswood. Stage 2 also includes the upgrading of existing overground rail between Sydenham and Bankstown to metro standards. Stage 3 - Sydney Metro West - will extend the service from Sydney CBD to Parramatta and Westmead via The Bays Precinct and Sydney Olympic Park. This element received AUD$3 billion in funding in June 2019 to allow investigation into the best route, location and design of stations, and the start of the approvals process.