A highway project in one of Australia's fastest-growing regions has broken tunneling speed records, excavating up to 163 ft in a day. The $1.33-billion Legacy Way project (formerly known as Northern Link) in Brisbane is currently running six months ahead of its scheduled mid-2015 completion, say officials.
To build the 2.9-mile-long parallel tunnels between Brisbane's Toowong and Kelvin Grove, the two 41-ft-diameter, 361-ft-long Herrenknecht double-shield pair of tunnel boring machines (TBMs) excavated more than 35.3 million cu ft of spoil, consisting predominantly of Neranleigh Fernvale and Bunya Phyllite, says Fernando Fajardo, executive director at Acciona Infrastructure Australia and project director for the Transcity Consortium. The consortium consists of Australia's BMD Constructions, Italian tunneling company Ghella, and Spain's Acciona Infrastructure. The design alliance consisted of Australian firms Cardno, and GHD and San Francisco-based URS, with urban design provided by Australia's RPS. Transcity will be remain in charge of operations and maintenance for 10 years after opening.
The TBMs were constructed from recycled parts of the TBMs used on the $2.85-billion Clem Jones Tunnel under Brisbane River, completed in 2010. Each of the 3,087-ton TBMs for the Legacy Way was assembled from 50 steel segments. A total of 38,700 precast concrete ring segments, each weighing 8.3 tons, make up the structural lining of the tunnels. The team also excavated 37 cross-passages, each measuring 33 ft long and 13 ft wide, and two substations. Construction began in spring 2011.
To alleviate traffic for the 1.27 million Brisbane residents projected by 2031, the Brisbane City Council embarked on the TransApex program of new bypasses connecting the city's existing roadways. The Legacy Way tunnel, the fourth of five TransApex projects, will link the city's western and inner northern suburbs, which will allow motorists to avoid seven sets of traffic lights and almost halve peak-hour travel times, according to the council. "It will help reduce the cost of avoidable congestion, which could rise to $3 billion [US$2.67 billion] per annum by 2020 if traffic issues are not addressed," a council spokesperson says.
One cent from every toll collected from the tunnels, expected to raise $535,000 in the first five years, will go to support the Legacy for Australia Defence, an organization that supports families of war veterans. The first TBM was named Annabell, after the daughter of a lance corporal killed in action in Afghanistan in 2011; the second machine, Joyce, was named after a World War II nurse. Joyce completed the 163-ft-in-a-day feat.
One of the main technological innovations on Legacy Way was the system to remove the spoil from the tunnel. Instead of trucks, the team used a 1,739-ft-long underground conveyor to move the spoil to the Mount Coot-tha Quarry, eliminating 100,000 haulage truck movements from local streets, according to Fajardo. The 10-month tunneling operations completed in June, and the spoil conveyor was then used to transport roadway materials back into the tunnel.
The traffic interface overall was a major concern addressed during the design phase. The project also includes lengthening and widening the off-ramps and adding extra turn lanes to the connecting surface roads, and the team was able to complete 90% of the work behind barriers for a seamless transition for motorists.
To reduce further traffic movement in and outside the tunnels, Transcity built an onsite plant to produce the grout used to fill the space between the concrete ring segments and the tunnel walls, which it then piped in. This two-component grout has never been used for large-diameter hard rock TBMs, where the gap is usually filled with pea gravel, says Fajardo.
"One particular challenge faced with this approach was ensuring the grout provided enough viscosity to guarantee that the entire void behind the segments was filled completely. It was also imperative to create the optimal gel time required so as not to allow grout to flow behind the shield, which would ultimately cause a blockage of the TBMs," Fajardo says. Transcity ran laboratory tests and large-scale trials to get the right mix. "This is one of the key factors for the high ring-build quality and watertightness of the joints in between the segments," Fajardo adds.
To expedite the project, Transcity also aligned the necessary permanent piling with the temporary acoustic shed and the TBM launch box. To simplify TBM disassembly, the team opted for a hydraulic driven and rail-based jacking system rather than cranes, which also reduced the impact on the surrounding environment, according to Fajardo.
Outreach efforts included door-knocking 3,000 homes along and near the alignment, in addition to phone and email notifications and a 24/7 community hotline, according to the city council.
In 2014, the team will switch to mechanical and electrical fit-out, overseen by Transcity JV and RCR O'Donnell Griffin. This will include installation of 98 jet fans for ventilation and smoke control, lighting, signage, CCTV, water pipes and other fire fighting equipment, emergency telephones every 60 meters, and a public address system. In addition, the team will finalize road paving, line marking, and installation of barriers, and continue civil and structural work on the surface. This work will take approximately 18 months.