Horizontal directional drilling (HDD) has become an important construction option for installing underground electric distribution cable.
A relatively compact drilling machine can quickly drill a precisely-guided pilot hole, then pull conduit to hold cable back through the hole. HDD limits excavation, avoids cutting across streets and landscaped areas and greatly reduces the amount of restoration required after an installation is complete.
The first directional drilling equipment small enough for utility work was introduced in the late 1980s, but HDD rigs weren’t seen regularly on job sites until the early ‘90s.
HDD was used to install underground electric distribution cables in the early stage of the technology’s emergence.
In fact, among the first compact drilling machines sold in the state of Georgia were purchased specifically to replace old and failing power distribution cable.
The construction manager of electric co-op Cobb EMC, Marietta, convinced management that the new technology, properly implemented, could make underground installations at less cost than conventional excavation construction. A key factor was reduced restoration costs.
That was a bold statement at a time when many considered the machines a novel experiment, and drillmakers were busy conducting demonstrations to convince utilities and contractors that the technology was viable for utility construction.
Cobb’s machines were early Ditch Witch Jet Trac models.
“Their power source was separate from the drill carriage and connected with a tether,” said Dennis Crowe, one of the Ditch Witch demonstrators.
“The drill frame could be rolled around by one crew member. Tracking equipment hadn’t been developed yet, so we used a utility locator to monitor location and depth. Steering required knowing the orientation of the face on the drill bit, and we marked each piece of drill pipe to indicate its orientation and made steering adjustments from that information.”
Obviously, equipment and guidance systems have evolved significantly.
Cobb EMC, one of the largest electric membership organizations in the nation, continues to take advantage of horizontal directional drilling.
“HDD has allowed us to upgrade our infrastructure in older developments without having an impact to our members’ property or a disruption in providing service to these members,” said Alex Newsome, Cobb EMC director of line maintenance and service operations. “We use HDD in situations where we are upgrading aging electric cable and in new construction where there are limitations in digging due to landscaped or paved areas.”
Newsome said Cobb EMC currently has three HDD crews and uses several contractors to perform directional drilling work.
In Virginia, directional drilling plays an important part in Dominion Energy’s Strategic Underground Program (SUP).
“SUP is a system-wide initiative in Virginia to shorten restoration times following major storms by placing certain outage-prone overhead electrical distribution lines and equipment underground,” said Alan Bradshaw, Dominion’s SUP director.
A data-driven process is used to select which overhead tap lines to convert to underground. The process begins with a review of 10 years of outage data for each tap line. The data is used to develop an “events per mile” metric to ensure selection of tap lines that will have the greatest impact for the lowest cost.
“We utilize directional boring almost exclusively with SUP as opposed to open trenching, and it has been key to customer acceptance and willingness to install underground lines in their area,” he said. “SUP projects serve established properties where customers have installed sheds or built fences and planted gardens. The ability to safely install facilities using a trenchless technology allows for minimal impact on established properties.”
For other construction, Bradshaw said most cable installations for new service typically are trenched, HDD is utilized in most instances where established properties must be traversed.
Dominion has five contractors assigned to seven geographic areas throughout its Virginia service territory.
“Each contractor provides design, right-of-way and construction services. While they are installing new underground facilities, they also are securing easements and completing designs for future work. They build their own backlog and, in many ways, are responsible for their own success,” Bradshaw said.
Discussing the economics of HDD, Bradshaw noted that prices have dropped while an increasing number of utilities use directional drilling.
“There are savings associated with not having to work around above- and below-ground obstacles,” he said. “Certainly there are responsibilities around identifying below ground facilities with both trenching and HDD, but being able to go under those facilities versus working around them is a huge benefit. Also not having to maneuver equipment around in tight spaces as frequently is a cost- and time-saver. And most importantly is being able to minimize disruptions on customer’s properties. For Dominion Energy, this is essential to the sustainability of SUP.”
Customer response is “overwhelmingly” positive.
“We recognized early on that respecting personal property was important to our customers,” Bradshaw said. “Although directional drilling is less invasive, it is still a construction project and customers will still see dirt. When our cable crosses other existing underground utilities, we pothole to expose underground utilities. Under the Code of Virginia’s Underground Utility Damage Prevention Act, potholing is used to ensure there is enough clearance to safely install the new underground cable.”
Disturbed surfaces are carefully restored.
“We have a commitment to leave private property as good as we found it,” he said.
Dominion Energy had been successful using directional drilling in all portions of its service territory, Bradshaw said.
“In Virginia, we have very different geographic terrain—from sandy soils on the East Coast to the rocky terrain in the Blue Ridge Mountains. In all instances and in any terrain, directional drilling is able to perform and safely install cable,” he said.
In Oklahoma, Edmond Electric is a municipal-owned electric utility that also has a history with horizontal directional drilling.
In 2002, the company initiated a program to replace overhead cable downed by an ice storm with underground cable with HDD equipment completing much of the work.
Currently in Edmond Electric’s five-year plan and budget, locations are identified where aging overhead lines will be replaced underground, said Dean Sherrick, distribution superintendent.
“HDD is most often used in established, landscaped residential yards, underneath roadways, and areas where surface disturbance needs to be minimized,” Sherrick said. “Directional drilling still is more expensive than trenching, but the customer satisfaction and not having to follow-up with landscaping seem to offset each other. Customers are more satisfied with construction that does not have to be followed with new landscaping.”
Directional-drilling work is awarded to contractors through competitive bidding.
“Our in-house crews, work closely with the contractors to ensure proper installation depths and minimal surface damage is achieved," Sherrick said. "We inspect the work to be performed, and we have the option to have the contractors install the cable in conduit or install the cable ourselves. We have also recently started using cable in conduit (CIC) as a way to shorten the duration a project may take, which seems to balance the cost/satisfaction out in the long run.”
Located adjacent to Oklahoma City, Edmond Electric services 83,000 customers.
Michigan’s largest energy provider, Consumers Energy, employs directional drilling in many situations.
“For electric distribution, we use directional drilling under roads, parking lots, county drains, and situations where we are trying to preserve the aesthetics of customers’ property,” said Keith Kurdziel, distribution standards and materials senior engineer. "An example is replacing an existing failed underground service under a landscaped, well-manicured lawn. We also use HDD in situations where we are unable to trench, such as hills and wetlands.”
Consumers Energy subcontracts its HDD work. Kurdziel said many subcontractors use 22,000-lb. pullback machines. Subcontractors like this machine because it fits through customer fences and works most of the time for up to 6-inch bore shots. They also have smaller units such as those with 11,000-lb. pullback force. Depending on soil conditions and size of conduit they may use 40,0000 or 50,000-lb. pullback machines.
One of the primary reasons for using HDD, Kurdziel added, is worker safety by minimizing the risk of trenching into unknown underground facilities and in areas such as hillsides where it is unsafe to use conventional trenching equipment. It also must be used where municipalities or the Michigan Department of Transportation require boring for crossing under roads.
Costs for directional drilling typically are more expensive than trenching, Kurdziel said. However, there are circumstances where boring is less expensive when considering all factors such as property restoration. It’s also true that in some cases, HDD is the only option.
Kurdziel said the use of directional drilling has increased in the past several years, and he expects that trend to continue.