Tunnelling down under
Feb 22, 2006
Tunnelling and underground construction projects continue to boom in Australia and New Zealand, driven largely by the rapid urbanisation of capital cities.
Australia has experienced rapid growth in the civil tunnel industry over the last decade, driven by the increase in projects in all major cities. Coupled with the minerals boom requiring large underground mine development work, Australia is a mature nation when it comes to tunnelling projects and expertise.
Project delivery mechanisms in the road infrastructure industry are forward thinking with Build, Own, Operate and Transfer (BOOT) being the most common framework. In particular, when it comes to toll roads and tunnels, the model is that of private investors building infrastructure at their own financial risk, under long-term agreements that allow them to recoup investments through tolls. Design and Construction (D&C), Design, Construct and Maintain (DCM) and Alliance are also widely used.
Lane Cove Tunnel
Located north of Sydney CBD the Lane Cove Tunnel is a 6 km freeway primarily comprising of an electronically tolled 3.6 km twin tube tunnel and a 2.6 km upgraded section of an existing freeway. This project is being constructed under a BOOT contract at a cost of $A1.05 billion with a 33 year concession period. The tunnel is being excavated using road headers with support provided mainly using permanent rock bolts and shotcrete in more problematic ground steel sets.
This project is a 400 m cut and cover tunnel under the Gold Coast Airport, and will be part of the $A392 million Tugun Bypass. The tunnel will be 27 m wide and 8 m high and be built 2 m below the existing ground level. The two carriageways will be separated by a central wall. The D&C contract was awarded in January 2006 and is expected to be completed in 2009.
The EastLink (previously Mitcham to Frankston Freeway) project is a $A2.3 billion, 39 km electronically tolled tollway linking the towns of Frankston and Dandenong to the Eastern Freeway in Melbourne’s east. As part of the tollway a twin 1.5 km driven three lane tunnel is being constructed. The tunnel has been designed to be tanked and undrained with a primary support system of rock bolts to allow construction to proceed with an in-situ un-reinforced concrete arch and a reinforced concrete invert as secondary lining. The project is due for completion in November 2008.
The Northern Gateway Alliance is currently implementing the ALPURT B2 motorway extension of SH1 north of Auckland for Transit NZ. The project extends 7.5 km and at $NZ335 million, the ALPURT B2 is the largest single road project undertaken in New Zealand. The motorway includes twin 340 m fully lined tunnels, each 12 m wide and 9 m high. The overall motorway project will be complete by mid 2009.
The following road tunnel projects are in various stages of planning:
A 4.6 km twin three lane tunnel connecting Sydney’s main western freeway (M4) with an inner city freeway.
F3 to M2 Connection
An 8 km twin road tunnel linking Sydney’s main northern freeway (F3) with the Sydney Orbital at the M2.
Brisbane North South Bypass Tunnel
Proposed BOOT $A2.1 billion electronically tolled road tunnel connecting Woolloongabba, Kangaroo Point and Bowen Hills.
Proposed $A1.96 billion electronically tolled BOOT road tunnel connecting the North South Bypass Tunnel with two of Brisbane’s main northern arterials, the Gateway Motorway and Brisbane’s airport.
Brisbane Northern Link
The Northern Link is a cross city tunnel linking Brisbane’s main western freeway with an inner city bypass and hence North South Bypass Tunnel and Airport Link.
Auckland Motorway System Tunnels
Transit NZ is planning two tunnels on the Auckland motorway network – one linked to the doubling of the SH1 motorway section and the other as an option for part of the SH 20 Waterview motorway.
Milford Dart Tunnel
The Milford Dart Tunnel is a privately conceived and financed 10.5 km tunnel proposed to form a new tourist route between Queenstown and Milford Sound in New Zealand.
- Bells Line of Road, a 1.2 km tunnel to the west of Sydney;
- Cairns to Western Tablelands Road link, a 7 km twin road tunnel in far north Queensland;
- Toowamba Bypass, a 42 km road which includes a 735 m twin tube tunnel at the top of the Great Dividing Range to the west of Brisbane; and,
- Inner Northern Busway, a number of tunnels planned as part of a multi-stage busway in Brisbane.
In addition to road tunnels, expanding Australian and New Zealand cities have increasingly turned to tunnelling as part of rail-based transport solutions.
Epping to Chatswood
The Epping to Chatswood involves 12.5 km twin tunnels with permanent concrete tunnel lining which is progressively installed. The spans in the stations are among the largest constructed in Sydney.
New MetroRail City Project
As part of the new $US1.12 billion Perth to Mandurah rail line 2.6 km rail tunnels and two underground stations under Perth’s CBD city are being constructed.
Auckland West Britomart Tunnel
A tunnel link from the west end of Auckland’s underground Britomart Station to surface on the Western Rail line near Mt. Eden has been proposed for many years, however funding for the massive project remains an obstacle.
In addition to the main road and rail tunnels there are a numerous utility and mining access and underground development tunnels proposed or constructed, principally driven by the minerals boom in Australia. The rapid growth of the tunnelling industry in Australia and New Zealand over the last couple of decades has resulted in its own set of challenges, some of which are set out below.
Paramount in any project is the safety of underground works, as highlighted by recent rockfalls during the construction of Sydney’s Cross City Tunnel. This incident resulted not only in project delays, but tragic loss of life. The result has seen vast improvements in ground support procedures and progress towards revision of national safety codes of practice for underground works.
Most current civil tunnels in Australia are constructed in hard rock; Melbourne in mudstone, Sydney in sandstone, and Brisbane in tuffaceous rock and folded sediments. Only Perth has tunnelling projects constructed in soft ground. Hard rock tunnels are generally well suited for road headers and hard rock TBM and the experience gained from such projects is assisting the tunnels technology internationally.
In many projects across Australia, groundwater has been a liability either due to potential for ground settlement or unexpected poor quality requiring treatment before discharge.
There is good news for the industry - improved D&C processes have resulted in development of thorough Quality Assurance/ Quality Checking models, greatly improved communication on technical issues, and stringent verification processes to ensure infrastructure meets suitable performance requirements. Safety improvements have been impressive and overall, Australia and New Zealand’s engineering capability is now well established and reputed.
This article was published with kind permission of Trenchless Australasia.
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