Electrical contractors who perform utility work have been burying electrical cable for years.
Trenchers and vibratory plows are routinely used to install underground cable and conduit, and firms that have added telecommunications construction to their capabilities use the same equipment to bury copper, fiber optic and coaxial communications cable.
Dependable utility trenchers and plows remain the fastest, most cost-effective way to extend
power and communications services to new developments and on projects where surface restoration and crowded easements are not issues.
Emergence of HDD
However, on projects where trenching is impractical or impossible, horizontal directional drilling (HDD) provides a mostly trenchless alternative for underground installations, completing work with minimal damage to surface improvements and reducing the disruption of traffic and other regular activities.
To make an installation, a compact HDD unit drills a pilot hole—through an easement, under lawns and flower beds, beneath streets, driveways and parking lots, even under rivers and steams—then pulls cable or conduit back through the hole. Directional drilling offers many benefits:
• University Project. Last month, Shawver & Son Electric, Oklahoma City, used HDD for direct burial of more than 60,000 feet of cable on the University of Oklahoma campus in Norman. The project included more than 50 directional bores ranging in length from 60 to 1,800 feet, totaling approximately 15,000 feet. The work was part of a project to expand and relocate the underground distribution network serving the university’s two high-voltage substations. Voltage is predominately 12.475kV, but a portion is 2,400V.
“Directional drilling was the only method of construction considered for work on the main campus because the university’s design team believed it would cause the least disruption to streets, sidewalks, lawns, planting beds, trees and shrubs,” explained Donald C. Carter, P.E., assistant director, engineering and systems operation, University of Oklahoma Physical Plant.
• City of Chicago. Next month the City of Chicago will finish—several months ahead of schedule—a $7.5 million pilot program to install two blocks of attractive new street lights in each of the city’s 50 wards. Ninety-five percent of the cable duct for the project—approximately 150,000 linear feet—was placed in landscaped parkways by directional drilling
“Minimizing surface disturbance is the primary benefit,” said Mike Quinlan, superintendent of construction for the city’s Bureau of Electricity. “Mayor Richard M. Daley believes preserving the environment of our neighborhoods is very important, and this project is one of his priorities. In fact, the city’s forestry department policy is that excavations should not be made in areas where damage could result to trees; directional drilling or some form of pipe jacking are to be used whenever possible.”
• Residential Rebuild. In the Oklahoma City suburb of Edmond, the first phase of a $1 million project to replace deteriorating aerial power cable serving the a neighborhood of 465 residences with new underground cable is complete. Approximately 30,000 feet of three- and four-inch HDPE conduit was buried.
“To minimize surface damage and inconvenience to residents, underground cable is being installed by horizontal directional drilling,” said Dean Sherrick, distribution superintendent for Edmond Electric, the city-operated provider of electricity. “The procedure limits the amount of excavation needed, greatly reducing damage to lawns, and makes it unnecessary to cut through streets and driveways.”
High-voltage cable goes in street right-of-way in front of homes; low-voltage lines are buried in backyard easements. City officials hope that ultimately all residential aerial power cables can be replaced.
HDD and electric construction
Directional drilling equipment has been used for electrical work since the first compact utility machines became available in the early 1990s. “Sizes” of directional drills are defined by pullback force, stated in pounds. Machines typically used to install electrical and communications cable range from 5,000 to 80,000 pounds of pullback, with most being in the 17,000-to-50,000-pound category. On the university project, five Vermeer drill units with pullback from 6,000 to 80,000 pounds were used; the Chicago lighting project is being done by Ditch Witch equipment with 8,600 and 17,000 pounds of pullback; work for Edmond Electric’s rebuild employs five Ditch Witch HDD models with pullback from 5,000 to 17,000 pounds.
Some electrical contractors do drilling with their own crews and equipment, while others subcontract drilling work; many do both. While there are electrical contractors who have used directional drilling for several years, the procedure is relatively new to many others.
PAR Electrical Contractors Inc., North Kansas City, Mo., has owned and operated horizontal directional drilling equipment for more than eight years, said Richard Holbeck, PAR regional vice president, Rocky Mountain East.
“We consider directional drilling to be a very important part of our construction capabilities,” said Holbeck. “We use HDD for feeder replacements and feeder upgrades in landscaped and developed areas, when working in close quarters, for boring under city streets, and occasionally for services. Ninety percent of HDD jobs are to pull in conduit.”
PAR also hires subcontractors for drilling.
Shawver & Son’s Robert Danner said his first experience with directional drilling for primary cable was in 2001.
“Now it comes up very frequently,” he said. “Electrical contractors who do underground utility construction must know and understand the capabilities of directional drilling. Whether they do the work themselves or contract it out, it is a growing part of today’s projects.”
For contractors considering investing in HDD equipment, those experienced in directional drilling advise that for productive, safe operation, crew members must be properly trained and experienced. Basic operational training is available through manufacturers and their dealers. In addition, managers of successful HDD operations say equipment should only be operated by personnel dedicated specifically to HDD work; it is unrealistic and potentially dangerous to expect operators of conventional equipment to be effective HDD crew members without training and experience. Some firms who add HDD services hire experienced personnel to operate drilling equipment.
Trenchers and vibratory plows
While directional drilling is suited for projects where it is important to avoid surface damage or excavations can’t be made, much underground construction continues to be done by trenching and vibratory plowing. While today’s trencher models may appear similar to those of the past, they are more productive, versatile and durable than earlier equipment.
Trenchers for electrical projects range from compact handlebar models to larger four-wheel-drive machines that can do several underground tasks when equipped with attachments. A popular configuration for utility work is a four-wheel-drive tractor with a utility backhoe and backfill blade on the front and combination trencher-vibratory plow component on the rear. Hydraulic boring attachments permit short, unguided bores under sidewalks and driveways.
In many situations, vibratory plowing can make installations with significantly less turf damage than trenching. To make an installation, a vibratory plow’s blade slices through the ground, burying cable or pipe that either feeds through a chute in the blade or is pulled behind the blade and into the ground. Depending on soil conditions, turf disturbance is limited to a small slit left by the path of the blade, making restoration much faster than filling in open trench. EC
GRIFFIN, a construction and tools writer from Oklahoma City, can be reached at 405.748.5256 or email@example.com.