Our neighbors at Dulles Corridtor Metrorail Project, which is building the new subway line through McLean and Tysons Corner, sent along this update on construction. The first 11.5 mile  phase of the Silver Line runs from the West Falls Church station to Wiehle Drive in Reston.

Building the subway guideway now overwhelms Route 123 near the Westpark Bridge which connects the Galleria Drive area and Tysons Corner Center.(Tysons I and II.)
 
Using a complex segmental bridge construction process involving huge cranes, crews from Rizzani de Eccher, headquartered in Italy, are using those horizontal cranes, known as trusses, to erect the structures. Each truss is about 360 feet long and weighs 365 tons.
 
Two of the horizontal cranes are now in use and a third is being assembled adjacent to I-495. Early in 2011, crews will use it to build the bridges over the Beltway. This will take 11 to 12 months to complete. Also, aerial bridge construction will take place next year along Route 7 from the site of the Tysons Central 7 Station near SAIC and the Marshalls shopping center west to and joining more aerial bridges at the Dulles Toll Road intersection where tracks will then lead westward to Reston using the median of the Dulles International Airport Access Highway/Dulles Toll Road corridor.
 
The bridges are built by connecting large concrete segments that are approximately 20 feet by 16 feet by 10 feet deep, large enough for workers to work inside segments suspended in the air. Approximately 2,700 segments are being built at a construction site located at Washington Dulles International Airport. Each segment is custom engineered to fit the design. Once fabricated, each segment is then transported from the airport via truck to the spot where it will be lifted into a span in Tysons Corner.
 
Fun Facts about the Horizontal Cranes:
 
    · In January, three will be operational in Tysons Corner
    · Each truss weighs about 365 tons and is 360 feet long
    · It takes 6 to 8 weeks to assemble the parts of a crane on-site
   · About 2,700 concrete segments will be used to build bridge spans between piers
    · A post-tensioning process is used to pressure the segments into bridge sp

Tunnel miners in Tysons Corner reached a second major milestone on Dec. 3 with the completion of the excavation for the inbound tunnel to carry trains from the future Tysons Central 7 Metrorail Station near SAIC and Marshalls to the Tysons Central 123 Station at Route 123 and Tysons Boulevard.

The parallel outbound tunnel was completed on Oct. 20.

Dulles Transit Partners, the design-build contractor for the Metropolitan Washington Airports Authority who owns and manages the project, are self-performing the tunnel construction. So far, more than 150,000 man-hours have been poured into tunnel construction.

During the mining process many, many truckloads of muck were transported from the tunnels to Dulles Airport where a rail yard will be built in Phase 2 of the Metrorail Project.

Tunnel crews have now started the next phase of construction, which includes waterproofing and installation of reinforced steel lining materials.

The tunnels will carry trains below the highest natural point in Fairfax County at the intersection of Routes 7 and 123.

Tunnel Mining Highlights:

   · A shotcrete plant at Route 123 and International Drive provided 20,000 yards of a special cement mix to build the tunnel rim
   · Approximately 100,000 cubic yards of muck were transported from the tunnel to Dulles Airport
   · At its deepest point, the tunnel is 35 feet below ground