APM Dulles International Airport

Automated People Mover

Clark, in a Joint Venture with Atkinson (a wholly-owned subsidiary of Clark) and J.F. Shea Co., is serving as General Contractor and performing the support of excavation, cast in place concrete for cut and cover tunnels and stations, New Austrian Tunneling Method (NATM) and Tunnel Boring Machine (TBM) method. The project also includes construction of a Tier One Station, a Tier Three Station Shell, an inner Spur Track using the cut-and-cover method and a tunnel portal at the Vehicle Maintenance Facility. Further, Clark is performing the MEP fit-out of the tunnel stations as well as installation of the Emergency Radio Supplemental Radiating System (SRS) for handling emergency communications with Metropolitan Washington Airport Authority, Loudoun and Fairfax Counties.

In total, traditional cut and cover construction encompasses more than 6,775 linear feet of rock excavation averaging a depth of 50 feet. This construction will allow for the concrete work involved in casting the twin box tunnels and two stations. Steel rock bolts and shotcrete facing will provide the excavation support to the in-situ materials. This portion of the contract represents the largest shotcrete job in the history of Clark.

The diameter of the TBM tunnel is approximately 20 feet and consists of over 2,100 linear feet of twin bore length. Two custom machines, known as moles, will bore through solid rock, utilizing multiple cutting wheels mounted into a face shield. Precast concrete wall lining segments are mechanically put into place by the mole as it continues to move forward.

Located on the northern end of the project, the NATM tunnels consist of 800 linear feet of excavated tunnel. In the NATM method, the tunnel is mined utilizing more conventional excavation equipment that must dig through the tunnel face in three-to-five foot ‘bites’. Onsite engineers determine the actual excavation sequences and drift lengths.

The Tier One station incorporates finishes and MEP systems similar to those found in the local Metro subway system. The Tier Three station will be finished to the shell stage, as it will be used as a future station for a yet-to-be-constructed concourse.