The New Jersey Department of Transportation decided to build an alternate route to alleviate the traffic congestion through the city streets of Trenton, New Jersey. The cut and cover tunnel was designed to provide easy passage on the heavily traveled Route 29. Several contractors pursued the design-build contract, however, PKF Mark III/NCI Joint Venture received the award to design a cost-effective tunnel using prestressed concrete. DMJM+Harris, the structural engineer, designed a bonded post-tensioned solution that reduced the mild steel requirement while permitting longer concrete pours. The contractor was able to increase the pours from 50 feet to 100 feet, thus reducing the overall project schedule by 50 percent and saving the owner time and money.

Longitudinal post-tensioning was used in the tunnel base slab, walls and roof slab. Additional transverse post-tensioning was added to the roof slab to provide reinforcement for the 3-foot soil backfill for a community park.

The multistrand post-tensioning system consisted of 3-strand tendons in the center wall, 12-strand tendons in the east wall and 17-strand tendons in the base slab. Larger, 31-strand tendons were used in the roof slab where the tunnel reached a maximum width of 110 feet. The tunnel's west side was designed with equally spaced 3 foot columns creating an open view of the Delaware River.

To maintain a constant tendon force throughout the 3,400 foot tunnel length without excessive use of expansion joints, VSL installed couplers that joined previously stressed tendons at each construction joint to ensure continuity of the PT system.

During construction, VSL furnished and installed the post-tensioning system. Including VSL as a member of the design build team proved to be valuable to the owner and general contractor by reducing the overall construction schedule and making efficient use of technology with VSL construction systems. The entire project was completed in 20 months.