Site Supervision & CM, QA/QC

The Cumberland Gap Tunnels are two dual-lane highway tunnels with a length of 1300m each, connecting Kentucky and Tennessee through the Cumberland Mountains. Because of the complex, variable geology and economic considerations, the New Austrian Tunneling Method (NATM) was chosen. The tunnel design included five excavation and support classes with rock dowels, lattice girders and reinforced shotcrete as primary lining. The final lining for the twin tunnels and 13 cross passageways was designed as cast-in-place (CIP) concrete with a flexible membrane waterproofing system.

An extensive underground people-mover train system and a fixed walkway tunnel between terminals are central to a multi-phased mega program of modernization and expansion for the Washington Dulles International Airport. The pedestrian walkback tunnel, a part of the expansion plan, crosses below two airport taxilanes and will connect the Main Terminal with Mid-Field Concourse B. The tunnel was designed as a multiple-drift NATM excavation, whereby cover beneath the taxilanes was less than a tunnel diameter at only 4.5 m. Excavation was therefore designed as a very controlled sequence with top heading excavation further divided into two side drifts.