To those in the financial sector, fall 2008 will live in infamy as a period of crisis and turmoil. With banks collapsing and non-stop talk of government bailout, economic slump was the buzzword around the world.

Despite this, in November 2008 Seattle region voters approved a multi-billion-dollar ballot measure that adds regional express bus and commuter rail service, building 36 miles (57.9km) of light rail to form a 55-mile (88.5km) regional system. A city already home to several tunnelling projects would ensure work for the industry for years to come.

Light rail
Called Sound Transit Two (ST2), the USD 17.8bn measure includes several extensions that will likely see tunnelling or some variation of underground construction. With the University Link (U-Link) project under design at the time of the measure, this made possible a northern extension from its University of Washington Station.

The 4-mile (6.4km) Northgate Link extension is mostly underground and likely to use three TBMs once the contract is bid and awarded this year. The USD 2.1bn project will terminate in Seattle’s Northgate (see article, p.15). From there, the ST2 plan includes another light rail extension to Lynwood, which will be primarily elevated.

An extension to the east will connect Downtown Seattle to a transit center in Redmond — home of Microsoft — by light rail with several smaller tunnels planned, although an alignment is still under discussion, in part, due to funding disputes between Sound Transit and the City of Bellevue.

The final price tag for the East Link project is expected to change from the current figure.

Who’s Working?
Sound Transit, the agency in charge of rail, bus and commuter services in the Seattle area, bid the 3.15-mile (5.07km) U-Link tunnels in two construction contracts. A joint venture of Traylor Bros. and Frontier-Kemper used two 21ft (6.4m) diameter Herrenknecht TBMs to excavate twin tunnels from the University of Washington to Capitol Hill. Spring 2012 saw successful breakthroughs for both machines, even with minimal cover beneath Montlake Cut.

From downtown Seattle to Capitol Hill, the JCM joint venture (Jay Dee/Cullucio/Michels) used a Hitachi Zosen EPBM to excavate 3,800ft (1,158m) of twin tunnels, relaunching the machine for a second drive after a late 2011 breakthrough, and making a final breakthrough in June 2012.

As of November 2012, all cross passages on both contracts are now complete, according to Sound Transit.

Meanwhile, a contingency from the Washington State Department of Transportation and contractor Seattle Tunnel Partners (STP, a joint venture between Dragados USA and Tutor Perini Corp, with Frank Coluccio Construction and HNTB, among others) visited Japan in December 2012 to check in on the USD 80M Hitachi Zosen TBM that will excavate the Alaskan Way Viaduct bored replacement tunnel.

Testing is expected to complete on the machine in January, then crews will disassemble the machine into 41 pieces for shipping to Seattle.

Once it arrives, the TBM will be assembled in the launch pit with a summer start for excavation.

The 1.7-mile (2.7km) tunnel beneath downtown Seattle has a 57ft (17m) excavation diameter.

Despite the amount of work going on in the city Don Davis, executive project director with Sound Transit, says the labour market is quite good. "There have been short periods where the contractors didn’t get as many miners as they may have wanted to put on for doing work simultaneously," referring to building cross passages at the same time as tunnelling work.

"Overall because we have had a number of tunnel projects, we have people who do tunnelling and like Seattle who either live here or are willing to come to work here, and they support our projects."

San Francisco update
Another city seeing quite the tunnel boom is San Francisco, and 2013 looks to be milestone year for several projects.

Robbins is currently working on two EPBMs it will provide for San Francisco’s Central Subway project, expected to launch later this spring.

The joint venture contractor of SA Healy and Barnard will excavate 1.7-mile (2.7km) twin bore tunnels in the USD 233M contract.

Meanwhile the city’s water system improvement program is planning two big milestones at two of its active tunnelling sites. The Bay Tunnel contractor, a joint venture of Michels, Jay Dee and Coluccio, anticipated breaking through — after 5-miles (8.04m) of uninterrupted tunneling across the Bay — early in January. Midyear, the 5.6km-long New Irvington Tunnel in Sunol Valley will see a holethrough at the final headings. Contractor Southland-Tutor Perini started roadheader excavation in 2011.