Tunnel boring machine completes second Beacon Hill light rail tunnel

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Sound Transit contractors punched through the east side of Beacon Hill in Seattle today, completing the second of two 4,300-foot tunnels through the hill for Link light rail trains to begin service in 2009. Obayashi Corporation’s 300-foot-long tunnel boring machine (TBM) nicknamed the “Emerald Mole” emerged within 5 millimeters of its target Wednesday morning.

“Link light rail in Seattle truly is seeing the light at the end of the tunnel, or tunnels in this case,” said Sound Transit Board Chair and Seattle Mayor Greg Nickels. “Later this summer we will be ready to pull Link light rail trains through the hill to test the trains on 10 miles of the finished tracks just south of the east portal as we prepare for the first passengers in 2009. This is a major milestone the thousands of men and women who have been a part of light rail construction from downtown to the Airport.”

Construction of Central Link began in late 2003 and is currently more than 85 percent complete and on schedule to begin service between downtown Seattle and Sea-Tac International Airport in 2009.

Light rail trains are currently making test runs between Sound Transit’s Operations and Maintenance Facility in SODO and the Downtown Seattle Transit Tunnel. Light rail trains are scheduled to make test runs from the Mt. Baker Station just east of the Beacon Hill tunnel through the Rainier Valley to Tukwila Station by the end of this summer.

Obayashi launched the TBM on its second trip through Beacon Hill in July, 2007 and excavated more than 50,000 cubic yards of soils as it made its way through Beacon Hill. In its path the 100-yard-long machine installed more than 800 pre-cast concrete segments forming the lining of the tunnel.

The tunnels tie in with the Beacon Hill station 160 feet below the surface. Both the tunnels and underground station are being built Obayashi along with the elevated Mt. Baker Station at Rainier and McClellan avenues.

More than 6 million man hours have gone into light rail construction since the project broke ground – work performed by union laborers, equipment operators, carpenters, ironworkers, masons, bricklayers, teamsters, electricians, plumbers and painters.

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