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Sound Transit contractors finished excavating the second of two 4,300-foot Beacon Hill light-rail tunnels after a tunnel boring machine (TBM) broke through the east side of the hill on Wednesday.

Obayashi Corp., which supplied the 300-foot-long TBM, began running the machine on its second trip through the hill in July 2007. Since then, the machine has excavated more than 50,000 cubic yards of soil and installed more than 800 pre-cast concrete segments to form the tunnel’s lining.

The Beacon Hill tunnel is part of Sound Transit’s Central Link project. Scheduled to open in 2009, the light-rail line will run between downtown Seattle and Sea-Tac International Airport. In summer, Sound Transit plans to test trains in the tunnel.