Liberty Tunnel Rehabilitation Project

Pennsylvania Department of Transportation (PennDOT)

Rehabilitation Design Services:

The Liberty Tunnel consists of two 5,888 foot (1,795 meters) long tubes, which run through Mount Washington in Pittsburgh, Pennsylvania. The tunnels provide a direct route to downtown Pittsburgh from the South Hills suburbs, easing traffic flow between the two locations. The Liberty Tunnel was opened to traffic in January 1924 and has since gone through a series of upgrades and repairs, including the installation of a ventilation system. In 2013, rehabilitation to the tunnels began which included the demolition and renewal of the ventilation arch walls (arch structure offset from the structural lining to provide for air-channels) inside the tunnels.

The original rehabilitation contract design proposed the use of self-consolidating concrete for the ventilation arch walls and supported the arch walls with radial hangers that were tied to the structural tunnel arch above. Gall Zeidler Consultants (GZ) provided an alternative rehabilitation design for the tunnels’ aging ventilation arch walls. GZ’s alternative concept used a self-bearing shotcrete arch wall and embedded lattice girders, which avoided the utilization of the radial hangers as well as the cast-in-place, self-consolidating concrete. GZ provided construction support services for the removal of the existing arch walls and the installation of the new self-bearing shotcrete arch.

The collaborative effort between the designer and contractor, allowed the work to be completed on schedule, below the original cost, and with much less construction risk for both the contractor and the owner.

Pittsburgh, Pennsylvania USA
2012 – 2013
Two twin tunnels
5,888 feet (1,795 meters) each
Conemaugh Group, including Glenshaw and Casselman formations(cyclic sequences of sandstone, shale, red beds, limestone and coal); Monogahela Group (cyclic sequences of shale, limestones, sandstone and coal); Pittsburgh Coal
Swank Construction Company
Pennsylvania Department of Transportation (PennDOT)