"The completion of the mining and concrete operations for the twin bores of the tunnel marks a significant accomplishment given that the section was considered the most complex engineering and construction phase of the project due to the tunnel's location," said George Morschauser, the project's executive director.
Construction of the tunnel began in October 2009 using the technique called the New Austrian Tunneling Method. Crews excavated a short section and then covered it with an initial lining of shotcrete. This process was repeated multiple times for both the inbound and outbound tunnels, which are each 1,700 feet.
Tunnel crews moved approximately 100,000 cubic yards of earth; sprayed 25,000 cubic yards of shotcrete for the initial liner; and applied 18,000 cubic yards of concrete for the final liner.
Crews will now install the track.
Bechtel-led Dulles Transit Partners is building Phase 1 of the Metrorail expansion project, which will include five new Metro stations and 11.6 miles of new track. It is scheduled for completion in 2013.