The dual 4.8 km twin-lane tunnels will link the Pacific Motorway (M3) and Ipswich Road in Woolloongabba, the Inner City Bypass and Lutwyche Road in Bowen Hills and Shafston Avenue in Kangaroo Point.
The NSBT is part of Brisbane City Council’s Transport Plan for Brisbane (2002 – 2016) and the Lord Mayor’s TransApex Project – the biggest urban road project proposed in Australia – aimed at filling gaps in Brisbane’s transport network to allow traffic to bypass the CBD.
Chairman of the Roads, TransApex and Traffic Committee, Councillor Graham Quirk said the NSBT was the first of the TransApex Projects to get underway.
“Traffic is an ongoing concern for many Brisbane residents,” Cr Quirk said, “and it is a problem that is going to get worse as Brisbane’s population of 1.8 million is expected to exceed three million by 2051.
“To keep our city liveable and to ensure economic prosperity, a solution had to be found.
“The NSBT is part of that solution; an exciting and much needed project that could cut up to 15 minutes off a peak-hour cross-city trip, reduce unnecessary congestion and free-up surface streets.”
Traffic
No new cross-river capacity has been provided since the Gateway Bridge was opened in 1986. Closer to the CBD, no new capacity has been provided since the Captain Cook Bridge in 1976. Capacity close to the CBD has been reduced by the replacement of general traffic lanes with bus only lanes on the Victoria Bridge in 2001.
The Federal Bureau of Transport Economics estimates traffic congestion costs Brisbane residents about $2.6 billion each year. This cost is expected to rise to $9.3 billion in just over a decade.
Five major roads that will link directly to the NSBT recorded an annual traffic increase of approximately six per cent in a survey completed in October 2006.
History
In late 2002, Brisbane City Council set up two independent task forces to determine the feasibility of the NSBT project.
The financial task force considered the project’s financial and commercial feasibility. The engineering task force aimed to develop a technically viable tunnel and identify key risks. Considerations included the tunnel’s depth and alignment in relation to the Brisbane River and the range of tunnelling options available.
The task force found a tunnel up to 60 metres underground, connecting Bowen Hills, Kangaroo Point and Woolloongabba, was technically viable.
Some of the challenges that faced engineers designing the NSBT included finding suitable work sites, minimising property resumptions, minimising any disruptions to essential services, safely connecting the tunnel ramps with existing roads in built-up areas, controlling tunnel water inflows during and after construction, spoil removal, managing community expectations and ensuring the environment inside the tunnel and near portals met appropriate national and international standards.
Partnering
Brisbane City Council chose to deliver the NSBT using a Public Private Partnership model that will see the private sector build, own, operate and maintain the tunnel for approximately 45 years.
On 30 June 2005, the Council issued tender documents and two bids were received from world-class consortiums – RiverCity Motorway and BrisConnections. Both tenderers submitted impressive but different bids that delivered innovative enhancements over the reference design.
After a lengthy review process by an expert Evaluation Panel who considered the bids in terms of their legal, financial, technical, traffic and communication aspects, the Council’s preferred proponent was the RiverCity Motorway consortium. The principal members of the consortium are Leighton Contractors (Sponsor and Equity Underwriter), Baulderstone Hornibrook and Bilfinger Berger BOT (Sponsor and Equity Underwriter) and ABN AMRO Australia (Sponsor and Equity Underwriter, Joint Financial Advisor, Construction and Term Debt Arranger and Underwriter).
Tunnelling
According to Cr Quirk, Brisbane has unique geological conditions, therefore three different types of tunnelling methods were considered appropriate for the NSBT.
“Roadheaders have been introduced to tunnel the curved areas such as the on and off ramps. Each weighing 125 tonnes, they are capable of tunnelling approximately two lineal metres a day. They are electrically powered and use a rotating cutterhead equipped with tungsten-tipped picks to cut the rock. The machines use sophisticated sensor guidance systems to enable the operators to control exactly the roadheader cutting process.
“Currently, six roadheaders, soon to be seven, are in action on the north and south side.
“Another tunnelling method in use is cut and cover tunnelling. This is a simple method of construction whereby a trench is excavated and roofed over. This method is being used in locations such as the NSBT entrances and exits.
“For the twin lane tunnels, two Tunnel Boring Machines (TBMs) were purpose-built to handle Brisbane’s tuff rock which is between two to three times tougher than concrete (concrete is normally 32-40 megapascals and the tuff varies between 100-150 megapascals).”
Cr Quirk said a TBM was often referred to as an underground factory because it had the capability to grind away at the rock creating a circular profile, remove spoil material via an onboard conveyor and install precast concrete segments to form the tunnel lining by using onboard crane and erection systems. The TBM also uses a steel shield to protect operators whilst the tunnel lining is installed.
“The machines will be responsible for up to 70 per cent of all excavation. Spoil removed during excavation will be taken to a purpose-built enclosed load-out facility and removed primarily via the arterial road network.
“The first TBM has arrived from Germany and is being assembled at the Bowen Hills site. The second TBM will arrive in December and be assembled over a period of three months. The two TBMs will be used to simultaneously excavate the mainline tunnels, both starting at Bowen Hills and finishing at Woolloongabba,” Cr Quirk said.
“They have the capacity to create about 20 metres of tunnel each day. The precast facility at Eagle Farm is currently manufacturing the 37,000 segments required to line the inside of the tunnel at the rate of approximately 100 per day. A stockpile of up to 9,000 segments will be kept on-site.”
Nine of the precast concrete segments fit together to form a complete section of tunnel lining. To fit together, each segment must be within 0.3 of a millimetre of its intended size.
When the two 4,000 tonne tunnel boring machines are operational from March 2008, they will each install up to 90 concrete lining segments per day. The total amount of concrete to be used in the construction of the tunnel is 280,000 cubic metres.
At the peak of production, up to1,500 workers will be employed.
Saving water
Cr Quirk said that Queensland’s water restrictions have been taken very seriously on the project.
“Major water saving measures have been implemented across the project. Prior to the start of major tunnelling in December 2007, a large-scale salt water desalination plant will commence treating water from the Enoggera Creek, providing up to 600,000 litres of high quality water per day.
“This, together with recycled and treated water recovered from the tunnelling process will be used for all tunnelling water needs, the manufacture of concrete at the project’s pre-cast facility and all other construction activities that require high grade water.”
Other water saving measures being implemented include capturing roof run-off and installing rainwater tanks at all site offices and where appropriate, using chemical dust suppressants to help mitigate dust, thus reducing the amount of water needed by water carts and hydroseeding soil stock piles or exposed areas to mitigate dust. This reduces the need for water carts running up and down these exposed areas.
Safety
NSBT will provide for the egress of people within the tunnel, should it be necessary, with cross passages every 120 metres and emergency lighting for effective evacuation. There will also be disabled/wheelchair access ensuring impaired commuters are able to exit the tunnel if required.
The NSBT will have a one metre left shoulder and another 0.5 metre shoulder on the right side. Emergency vehicles will be available 24 hours a day, seven days a week, to deal with traffic accidents and breakdowns, all safe areas between the two tunnels will be fitted with fire doors, telephones and emergency equipment.
Other safety measures include a Tunnel Control Centre, a fire deluge system, backup power supply for emergency operation, mobile phone coverage, smoke control systems, emergency telephones adjacent to the left lane and surveillance cameras, to name but a few safety innovations.
Tunnel communications
Communication inside the tunnel will be possible via a number of means including a public address system, radio with a “÷break-in’ faciljavascript:nullo()
Boldity allowing direct one-way communication with motorists, mobile phone coverage and motorist help phones.
Urban renewal
Urban designers for the NSBT have ensured that the new road integrates with the existing Brisbane landscape.
Key considerations in the urban and architectural design of the tunnel included minimising visual and noise impacts, crime prevention principles, protection of creek corridors, bike and pedestrian amenities, reinforcing residential character and high quality landscaping.
The NSBT is scheduled to open in 2010.