Waterproofing & Water Control

The Lehigh Tunnel No.2, part of a 4-lane motorway running East-West through Pennsylvania, was one of the first tunnels in the US built using NATM. Capacity problems of Lehigh Tunnel No.1 caused delays during peak times. The new tunnel was excavated using top heading, bench and invert excavation with shotcrete support. To achieve a completely dry tunnel a PVC membrane was installed between primary shotcrete lining and the final cast-in-place lining. Tunnel rehabilitation including the installation of a PVC membrane and thermal insulation in the air duct was performed to the original tunnel.

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.