John Holland is awarded A$324 million construction of the two deep shafts that will service construction of the central section of the new A$11 billion Melbourne Metro in Australia.
Although the Environmental Review process is not due to finish until later this year (2016), project owner Melbourne Metro Rail – acting on behalf of the Victoria State Government – awards the Early Works package in order to facilitate early construction of the central section of the 9km alignment. Excavations will begin early next year (2017), once the Environmental approvals are granted.
The two shafts, both 35m deep, will be excavated close to the location of the new CBD North Station. They will facilitate access for construction of both the CBD North and CBD South stations, both to be built as mined caverns; as well as the roadheader-mined tunnel that connects them.
It is not yet clear whether the contract to build the central cavern stations and the 1,000m-long mined tunnels between them will be let separately to the main TBM running tunnel contract. This construction package is expected to enter the procurement phase next year (2017), ahead of contract award and the start of TBM operations in 2018.
According to recent concept alignment drawings prepared by the owner’s design team – the aurecon/Jacobs/Mott MocDonald (AJM) Joint Venture – the main running tunnels will be driven from portals built into cut-and-cover ramps to be constructed at either end of the 9km alignment. At its deepest point the tunnel crown will be 40m below the surface, although in some sections this distance will be as little as 10m, and at the undercrossing of the Yarra River it will be 7m – about the same distance as the diameter of the TBMs that will drive them.
It had been suggested that in order to save on project cost, the CBD North and South Stations, and possibly the tunnel between them, be excavated using the cut-and-cover top-down method. However this suggestion has been rejected on account of the surface-level disruption it would cause along Swanson Street, one of the main thoroughfares in the busy business district area of Melbourne.
In addition to the two cavern stations a further three cut-and-cover stations are to be constructed at Arden (situated 18m below the surface), Parkville (30m), and Domain (17m). The alignment also crosses just 5m under the existing City Loop rail tunnels close to the southern end of CBD North Station; as well as just 5m above the Burley highway tunnels of the City Link.
The Early Works Melbourne Metro contract win for John Holland is especially sweet given that it was part of the Momentum Infrastructure JV that lost out on design-build construction of the 4.4km East-West Link highway tunnel, also in Melbourne. That mega-project was awarded to the Buoygues/Acciona/Lend Lease joint venture, but then cancelled a few weeks later in favour of reviving the Melbourne Metro project instead.
A new political administration has killed off Melbourne’s East-West highway link and launched preparations for a call of EOIs to construct a new metro link through the heart of the city instead.
Melbourne Metro Rail announces TBM as the preferred excavation method for the twin tube crossing under the city’s Yarra River. Other methods considered, but rejected, include an immersed tube and a cofferdam construction method, but both were considered to be too disruptive.
A machine of approximately 7m diameter will be required to bore the tunnels, which will lie 7m below the bottom of the 4m deep river to the east of Princes Bridge. Announcement of the TBM methodology for the 50m river crossing makes it likely that mechanised tunnelling will be used for the majority of the 9km underground alignment.
Announcing the preferred methodology, Victoria State Premier Daniel Andrews said: “There is A$4.5 billion [of an estimated total project cost of A$9–11 billion] committed right now to this important project.”
Jacinta Allan, Minister for Public Transport, added: “Crossing the Yarra is one of the more complex parts of the Melbourne Metro Rail Project, which is obviously a massive project with the construction of twin 9km tunnels along the route.”
The project is currently still in the preliminary design phase, and will require the necessary planning and environmental approvals, but is scheduled to go into construction procurement in 2017 ahead of contract award in 2018.
The Victoria State Labour Party has carried out its pre-election threat to rip up the A$5.3 billion public-private partnership construction contract awarded in September last year (2014) to the East West Connect consortium of Lend Lease, Acciona and Buoygues. The project was to have included 4.4km of twin bored highway tunnels using mega-TBMs of up to 15m diameter.
The new State Government was elected in November – barely two months after the East-West Link contract was signed by the outgoing Liberal-led Coalition Government. Last week the State reached a deal with the East West Connect consortium under which it agreed to pay compensation of A$339 million, plus a further A$81 million in banking charges. An additional A$500 million has already been spent by the State Government on geotechnical investigations and reference design fees to bring the now-cancelled project to bid stage.
In its place, the new Government has revived long-running plans for a metro link through the heart of Melbourne’s CBD that had been shelved by the previous Government. The amended plan, estimated to cost up to A$11 billion, is now known as the Melbourne Metro Rail Project and includes 9km of twin running tunnels between portals at South Kensington and South Yarra, five underground stations, and an undercrossing of the Yarra River.
The newly packaged project is almost identical to the original Melbourne Metro Rail concept proposed in 2008 as part of the East West Link Needs Assessment. At that time the project was costed at A$4.5 billion, less than half the $9-11 billion price tag at 2013 prices. Much of the geotechnical investigation and alignment work is already completed. In 2009, Aurecon, in association with Mott MacDonald, Sinclair Knight Merz and Grimshaw Architects, acted as Technical Advisor for the development of concept designs as part of the 2010 business case for what was then known as the Melbourne Metro Project.
The work of this design team led to Infrastructure Australia designating the Metro Rail Project in 2010 as one of only a handful in the country that was “Ready to Proceed” – although a prolonged period of inactivity has meant this rating has since been downgraded a category to “Threshold” status. This means that the project is still considered to have “strong strategic and economic benefits” but requires “a small number of outstanding issues” to be resolved before it is deemed ready to proceed once again.
To this end the Victoria Government has budgeted A$1.5 billion of state funds for the new rail project, and is hoping to persuade the Federal Government to divert the A$3 billion it had pledged towards construction of the now-scrapped East-West Link Project to the metro scheme. On Tuesday (28 September 2015) Aurecon and Mott MacDonald – which both worked on the 2010 rail project – were re-engaged by the Victoria State Government this time as Technical, Planning and Engagement Advisor to the Melbourne Metro Rail Project and in joint venture with Jacobs (the AJM JV).
It is not yet clear which excavation methodology will be used, but the Government has announced its preference for a “shallow tunnel” just 10m below the surface and crossing above the existing Melbourne Rail Loop tunnels. This has the advantage of enabling easier and cheaper top-down cut-and-cover construction of the stations in the highly built up area of Melbourne’s CBD, but represents a major departure from the recommendations of the Engineering Design and Costing Report prepared as part of the 2008 East West Needs Study.
That study recommended a deep level (35-63m) tunnel to take advantage of the more straightforward mining conditions presented by the Melbourne Formation. The collected geotechnical data suggested that a shallow tunnel would result in the higher project risks of TBM excavation through a mixed ground of the basalt and Yarra Delta sediments, especially at the location where the alignment crosses under the Yarra River; the possible need to lower groundwater levels which might have the effect of increasing regional settlement of the Coode Island silts and cause damage to existing infrastructure; and the potential to undermine existing structural foundations.
EPBM and slurry TBM technology has, however, made significant advances since 2008, and new geological investigations at 140 locations will now be carried out along the alignment to reassess the geological and groundwater conditions. These are expected to be completed by mid-2016, to run alongside completion of a new reference design, the statutory planning process, and other early works. The procurement method and funding programme is not yet announced, but Expressions of Interest are expected to be called later this year or early next year.