Accessible. Large tunnel gives access for maintenance. (Photo courtesy of UNC Chapel Hill Construction Management)

Construction is proceeding in three phases, including one for the utility plant and two for separate tunnels connecting to the plant. Together, construction costs total $84 million. A joint venture of Whitaker Construction and Associated Brigham Contractors (ABC), both of Brigham City, Utah, expects to complete its lump-sum contract for 3,000 ft of tunnel in September. Clancy and Theys and Pipeline Utilities, both of Raleigh, N.C., are joint-venturing on a 1,300-ft-long tunnel.

Challenges include the hilly landscape, the 30-ft trench depth and a campus hospital that needs a long lead time before contractors may disrupt service to relocate existing lines.

"We’ve done a lot of traffic planning and construction phasing to ensure that the hospital’s operations aren’t interrupted," says Scott Clark, principal in charge for Fort Worth, Texas-based Carter & Burgess, the project’s engineer. He adds that the plant and tunnel were situated near the hospital to enhance the facility’s system reliability.

Excavating in the hilly terrain has been a special challenge. "We’ve had to blast out granite to make way for the tunnel, and work around existing utilities," says Judd Hamson, project manager for ABC and Whitaker.

To shore up the trench and prep the site for pouring the concrete floors and walls, contractors are using 100 8 x 20-ft trench shields supplied by Burlington, N.C.-based Coble Trench Safety, each of which weighs about 10,000 lb. "Many tunnels like these are sheet-piled," says Hamson. "But with this approach we’ve been able to handle the excavation in a safer, faster manner."

Once finished, the tunnel will house seven pipes, including two 30-in. chilled water lines, five low-pressure and high-pressure steam pipes, a 2-in. trap line and two 10-in. pumped condensate lines.

Calling the tunnel-utility plant combination "a cost-effective way to deliver power and service the campus infrastructure," Cameron Smith, UNC Chapel Hill's construction manager, says maintenance crews will access utilities through the underground structure’s 9 x 11-ft walkway. The top of the tunnel will be buried 8 to 10 ft deep, to allow future utilities to be placed above, he adds.

Completing the project is a utility plant constructed of cast-in-place concrete basement and topped off by a structural steel skeleton. When Frank Lill & Son, Rochester, N.Y., finishes it in the fall of 2006, the plant will house two water tube boilers that are connected to the tunnel system.