ASPIRE is a quarterly magazine published by PCI in cooperation with the associations of the National Concrete Bridge Council. The editorial content focuses on the latest technology and key issues in the Concrete Bridge Industry.
Issue link: http://www.aspiremagazinebyengineers.com/i/306189
The Dulles Corridor Metrorail Project, a two-phase, 23-mile extension of the existing 106-mile Metro rail system, will connect the nation's capital, Tysons Corner, and Washington Dulles International Airport. Construction of Phase 1, the first 11.6 miles, is nearly 50% complete. It will include five stations and multiple auxiliary power facilities and environmental controls. One of the project's biggest challenges has been working in and around this heavily congested area. Work sites are limited and narrow, mostly in the medians of the area's most traveled thoroughfares where traffic moves just feet away. "The safety of the traveling public and our employees is the top priority of this project," said George Morschauser, executive director for the project's design-build contractor. project orientation Phase 1 features nearly 3 miles of aerial guideway. The rest of the alignment will run at-grade except for a 2400-ft-long tunnel between two of the stations. There are three guideway sections in this new alignment: "O-1," "Tysons East," and "Tysons West." The O-1 begins at the eastern end of the project, where the new line will split from the existing Metro Orange Line. It features two parallel, 1600-ft-long guideways that fly over I-66, a major interstate highway. The other two guideways, Tysons East and Tysons West, are precast segmental concrete box girder bridges constructed using highly-visible trusses—massive machines that are unlike anything most of the area's traveling public has ever seen. The congestion of Tysons Corner was a main reason to use trusses for the majority of the guideway work instead o f g ro u n d - b a s e d c r a n e s . " We ' re using overhead trusses because they are the most efficient method," said Shawn MacCormack, the project's task manager for aerial structures. "They are ideal in dense urban environments like Tysons Corner because they use a 'top- down' construction method and have little impact on the traveling public." Traveling from east to west, once over the O-1 guideway, the rail line will descend to grade level for about 2 miles in the median of the Dulles Connector Road (Route 267). Then, the Tysons East guideway begins, crossing over into Tysons Corner, and into the first of the four Tysons Corner stations. From there, the rail will continue at an elevated level, ascend to its highest point— approximately 55 ft—over the eight- lane I-495 Capital Beltway and then descend into the second station where the rail line briefly goes underground. The alignment resurfaces in the median of Route 7 at the third station, which is partially underground. From there, the Tysons West guideway begins, running for about a mile and through the fourth station. One final flyover takes the guideway westward into the median of the airport access highway, descending to grade for the rest of the alignment. The fifth station is located approximately 4 miles west of Tysons Corner. How They're built The Tysons East and West guideways are being constructed using more than 2700 precast concrete segments that are fabricated in an off-site facility on Dulles Airport property. All segments are match cast. The short-line casting method is used for the typical main guideway segments and the shallower station segments use the long-line casting method. The segmental box is approximately 7 ft 6 in. wide by 8 ft deep, with a top flange approximately 16 ft wide for the profile DULLES CORRIDOR METRORAIL PROJECT AERIAL GUIDEWAYS / TySONS CORNER, VIRGINIA S ubSTruCTurE DESIgN ENgINEEr: Bechtel, Vienna, Va. S upErSTruCTurE DESIgN ENgINEEr: Corven Engineering Inc., Tallahassee, Fla. C oNSTruCTIoN ENgINEEr AND ErECTIoN TruSSES MANuFACTurEr: Deal, Pozzuolo del Friuli, Italy pr IME CoNTrACTor: Dulles Transit Partners, Vienna, Va.—a team of Bechtel and URS CoNCrETE SuppLIEr: DuBROOK Concrete Inc., Chantilly, Va. prECASTEr: Rizzani de Eccher USA, Bay Harbor Islands, Fla. by Shea Daugherty and Chris Jennions, Dulles Transit partners The Dulles Corridor Metrorail Project Connecting the Nation's Capital with its International Airport An aerial view of the Tysons East Guideway and the truss that has helped construct it. This guideway took about 18 months to complete and is more than a mile in length. Photo: Chris Jennions. 26 | ASPIRE , Fall 2011 Book_Fall11.indb 26 9/29/11 11:59 AM