Supporting tunnel excavation at Washington, D.C.’s, busiest airport

Serving the Washington, D.C., region, Dulles International Airport has seen strong growth in passenger numbers – serving more than 25 million per year. In preparation for reaching a 55 million passenger target, the authority launched a mega renovation and expansion program to improve the airport’s facilities including transport, taxiways and a new terminal.

The challenge

The project included a fixed walkway tunnel between the terminals and the airport concourses, which would need to cross below two of the airport’s taxiways.

Contractor Kiewit used the sequential excavation method to build the tunnel of 770ft length by 40ft width and 27ft height (235m x 12m x 8m). With less than one diameter of cover between the tunnel and vital airport infrastructure, the excavation required adherence to stringent control parameters to avoid disruption to flight operations.

The solution

The tunnel’s primary support comprised a 2-inch (50mm) flash layer of Dramix® ZP305 steel fiber-reinforced shotcrete applied immediately after excavation.

Lattice girders were then installed at a spacing of 3–5ft (1–1.5m), followed by another 6 inches (150mm) of steel fiber reinforced shotcrete.

A layer of plain shotcrete was used to finish the primary lining, preparing it to receive a PVC waterproofing membrane and the final lining.

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Supporting tunnel excavation at Washington, D.C.’s, busiest airport

The challenge

The solution

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