Excavation of Australia's longest ever rail tunnels is complete following breakthrough by the last of four 6.99m diameter NFM double shield TBMs for construction of Sydney's Metro Northwest (formerly known as the North West Rail Link).
Thursday's (14 January) breakthrough into what will become Cherrybrook Station completes 15km of twin running tunnels on the A$8.5 billion (US$8.9 billion) project. The central underground section, which was awarded to the Thiess/John Holland/Dragados (TJHD) joint venture in June 2013 for a contract sum of A$1.15 billion, represents more than half of the total 23km alignment between Cudgegong Road in the north west suburbs of the city, through to Chatswood where onward travel is available to the city centre and beyond. Five of the stations along the route will be located underground, and a 4.4km section will be constructed as an elevated 'Sky Train'.
Mechanised excavation of the 30km x 6.6m i.d. underground section of the alignment, which runs to a depth of up to 58m at its deepest point, began in September 2016 through a geology comprising mainly sandstone and shale. During 16 months of 24 hours a day, 7 days a week TBM excavation, TJHD recorded an average weekly progress rate of 173m. A purpose built factory located at the job site in Bella Vista manufactured 98,184 segments for the 16,290 rings of the tunnels.
At the high profile breakthrough ceremony New South Wales Premier Mike Baird said: "Today everyone can be proud at what’s been achieved, with this long-promised critical public transport project taking shape before our eyes. This rail line will transform the lives of people in Sydney’s north-west, enabling commuters to catch a train every four minutes in the peak."
Minister for Transport and Infrastructure, Andrew Constance, said: "I pay tribute to all the men and women who have worked on this massive project and ensured tunnelling has finished about two months ahead of schedule. About 2.7 million tonnes of Sydney Sandstone and shale has been excavated to complete the job."
The first TBM to complete its journey, Isabelle (TBM3), broke through at Epping Station on 18 September last year (2015) following a 6km drive (Fig 1). Sister machine Maria (TBM4) broke through at the same location at the end of October (2015) following completion of the parallel drive.
TBM1, Elizabeth, completed her 9km journey from Bella Vista through to Cherrybrook on 1 December (2015), ahead of final completion of mechanised tunnelling with the arrival of TBM2 (Florence) on Thursday (13 January).
Project scope has also included excavation of a large crossover cavern at Castle Hill to enable switching between tunnels in the event of service disruption, and to maintain a reduced service during tunnel maintenance.
The Sydney Metro Northwest project is the first stage of a 65km metro line that will eventually connect to Bankstown in the city's southwest via new stations to be constructed in the city's Central Business District. The so-called Southwest Metro project, valued at A$10 billion, includes excavation of 15km more of twin running tunnels and a new undercrossing of Sydney Harbour. The team steering Sydney Southwest Metro expects to hand a business case for the second stage of the public transport project to the Baird government within the next few months, and to that effect A$50 million of expenditure has been brought forward to accelerate delivery of that critical infrastructure.