Most project teams rely on building information modeling (BIM) to assist in planning, designing, and troubleshooting a project’s above-ground systems. But for the University of North Carolina Hospital’s (UNCH) Hillsborough Campus project, Skanska (Parsippany, N.J.) focused the technology underground, where it was used to provide rock evaluation for site preparation and coordinating underground utilities.

This four-phase, $156 million project on a greenfield site includes a three-story MOB, 14,000-square-foot central energy plant, and a 241,574-square-foot patient tower and treatment building.

To establish the existing below-ground conditions, the project team worked with a site surveyor on the building footprint and the location of the underground utilities, and hired a boring contractor to perform exploratory drilling in the proposed path of the water and sanitary piping, storm utility, gas lines, and duct banks. The data was added to the CAD drawings to show the team the rock elevations, and then was used to develop a 3-D model.

Findings showed that some of the original proposed routes for utilities would clash with rock. “We were 30 to 40 feet below grade with trench rock, which was very expensive [to excavate],” says Al Painter, project executive at Skanska. “So we talked to the owner and the design team about relocating the lines from the rear of the project to the front of the building to incur less rock.”

This adjustment saved the project more than $300,000 and eliminated more than 100 clashes between multiple site utilities, site utilities and rock, and site utilities and unforeseen conditions.

The team also used the BIM model to determine that raising the basement layer on the buildings up from 20 feet to 18 feet in floor-to-floor height would bring even further savings.

“You still have to mass excavate, but by reducing the basement height, you’re actually raising the level of the basement so you’re excavating less rock,” Painter says.

With three of the four phases completed, the design team is now working on the hospital, which is expected to be operational in July 2015. The readjusted basement height, however, means there’s less available square footage between floors than the original proposal.

“We’re now faced with the challenge that we have less space and we’re trying to coordinate above-ceiling utilities,” Painter says. “That’s where the modeling really helps out.”