Photo Courtesy Clark Construction Group

Construction of the APM was broken into several phases, and Tier 2 was the last contract to be procured. The Tier 2 project included the construction of an underground pedestrian tunnel and a vertical circulation building, which connects the existing Concourse C with the new APM Tier 2 Station via elevators and escalators.

The cast-in-place concrete pedestrian tunnel is 40 ft wide and 450 ft long and crosses under an active aircraft taxiway. The Clark team performed a 30,000-cu-yd soil and rock excavation that was 30 ft deep.

Excavation included supporting an existing 54-in.-diameter, reinforced-concrete storm-water pipe, and the design also took into account the additional loads of the adjacent aircrafts. The tunnel required 6,800 cu yds of concrete and 630 tons of rebar.

The tunnel contains two 250-ft-long moving walkways, and the walls follow a unique hexagonal shape. To achieve the desired effect, the concrete work required custom forms. Work in the tunnel also included relocating existing underground utilities, including a 12-in.-diameter jet-fuel pipe.

Clark had to maintain service vehicle traffic across the excavation. A temporary bridge was designed and constructed by Clark to serve as this roadway.

Passengers using the tunnels enter Concourse C through the new vertical circulation building. The building’s exterior consists of metal wall and roof panels and a section of single-ply membrane roofing. Four escalators and two three-story hydraulic elevators carry passengers the 38 vertical ft between the concourse level and the tunnel.

The finished ceiling is 35 ft above the finished floor and continues on a slope above the four escalators. In order to meet the schedule, construction on the escalators occurred simultaneously with the ceiling work above on an engineered scaffold. The scaffold system to install the ceiling was erected after the escalators were set in place.

Dulles remained fully operational throughout the project. Despite the added obstacle of working adjacent to an active taxiway, the team had a perfect safety record.

Key Players

Owner: Metropolitan Washington Airports Authority
Contractor: Clark Construction Group, LLC
Construction Manager: Parsons Management Consultants
Architect: Kohn Pederson Fox Associates
Civil Engineer: Urban Engineers Inc.
Structural Engineer: Amman & Whitney Consulting Engineers, P.C.
MEP Engineer: Ove Arup & Partners Consulting Engineers, P.C.