Low-Impact Directional Drilling Spares The Landscaping

By Tara Hansen | September 28, 2010

When performing a high-profile utility installation job — say, for instance, a project at the Georgia Governor's Mansion — there is more to consider than just getting the product in the ground.

NPL Construction Co. is used to such challenges. With more than 40 years in the business and nearly 3,000 employees working across the country, NPL specializes in electric, fiber, telecom, cable TV, and other utility installation plus distribution infrastructure services. So when its Georgia office was called on to install a natural gas line at the Governor's Mansion, the company stepped up to the task.

A Challenging Site

NPL was hired by Atlanta Gas Light Co. to install replacement gas lines in the area of the Governor's Mansion in northeast Atlanta. The mansion currently serves as the official home of Georgia's 81st governor, Sonny Perdue, and his wife, Mary. The three-floor, 30-room Greek revival-style home was built in 1967 and sits on an 18-acre site — and those beautifully landscaped grounds immediately surrounding the mansion would pose the first obstacle for NPL crews.

"We couldn't make a mess. We had to make no disturbance on the grounds," says Ray Harris, project superintendent for NPL—Georgia. "Before starting the job, we sat down with Atlanta Gas Light, the Governor's Mansion staff and our superintendent, and it took a while to plan."

To install the new 2-inch plastic gas pipe, NPL crews used a Vermeer NAVIGATOR D7x11 horizontal directional drill. Its compact size allowed crews to access the job site and maneuver within the confined area and around obstacles such as fences and landscaping features, and its light weight would minimize potential damage to the landscaping.

Two Shots To Complete The Bore

On the first day at the job site, NPL crews set up the drill in the middle of the yard and placed plywood underneath its rubber tracks to prevent any ground disturbance. At about 9 a.m. they began drilling the first shot of the 500-foot-long bore toward the mansion. Though the operator had to navigate to avoid irrigation, power, telephone, cable, and other utility lines, the first shot took only two hours to complete.

The second shot was a bit more complicated. Using the D7X11 Series II unit again, Harris and his crews bored in the opposite direction of the first bore — across the road to the gas main. Not only did existing utilities stand in their way, but they also had to drill under a brick wall with a wrought-iron fence.

"When we started the second shot, we had to stay level about 150 feet and then take a dive in pitch to get under the wall," Harris says. "It was all downhill to the wall and then it leveled off at the road. So we had to dive and level off quick at 3 feet deep. The hill set 6 feet above the road."

Harris says he knew he could start drilling deep after the first 100 feet and then level off over the next 100 feet, so that when they got to the wall they would be at a depth of 3 feet. This enabled them to cross the road, two fiber lines and a water main.

Minimal Site Disturbance

In all, six men were stationed on the job site. One three-man crew worked inside the gated area near the mansion and hand-dug the riser to the gas meter, while the second crew worked outside the fence line, locating the fiber-optic lines and water mains in the road. This crew also dug up the gas main to tie-in the new service.

By 2:30 p.m. that same day, NPL crews had completed the total 500-foot-long bore and were ready to pull back the new 2-inch plastic gas pipe.

The job was a success, Harris says, and was completed without damaging the Governor's Mansion landscaping.

"When we left," he says, "it was as if we were never there."

Author Information
Tara Hansen is a technical writer specializing in construction topics.