Report From the Underground

By Jeff Griffin | Sep 15, 2005
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Horizontal directional drilling (HDD) is an innovative “trenchless” construction procedure. It has been in use for a dozen years to make trenchless installations of cable, conduit and duct in areas where surface improvements or crowded utility easements make excavation impractical or impossible.

HDD has close ties with the electrical industry—it was one of the markets targeted by manufacturers of early drill models, which were used for reconductoring. As HDD equipment evolved, it was also used to place larger-diameter power cable and conduit for copper, coaxial and fiber optic communications cable.

However, not all electrical contractors are familiar with the directional-drilling process or understand in which situations it can be used as a viable alternative to trenching and plowing. Other utility markets have been faster to adopt the technology.

No matter what type of cable, conduit, duct or pipe is installed, the basic procedure is the same.

The drill unit launches a pilot bore, usually from the surface, and the drill head is carefully guided toward a predetermined exit point. The path of the bore is monitored by electronic tracking equipment, and changes in direction are made by adjusting the orientation of the bore head. When the pilot bore is complete, the drill head is brought to the surface or into an exit pit or manhole, the drill head is removed, cable or small-diameter conduit is attached to the drill string, and the product is pulled back through the pilot hole. If necessary, pilot holes are enlarged by back reaming to accommodate larger sizes of pipe.

Baker Electric, Des Moines, Iowa, is a directional drilling veteran, putting its first HDD unit in service in 1995. The company owns three drill units used on a variety of projects.

In 10-plus years of directional drilling, Baker has installed more than 500,000 feet of cable or conduit, said Roger Innis, Baker project manager/estimator.

“We do directional drilling on street-lighting projects, lighting in parking lots, raceways for traffic signal wiring and for telecommunications interconnects,” Innis said. “If a contractor is doing underground construction today, projects are likely to include segments of directional drilling. Almost every commercial job needs conduit buried, and if it isn’t practical to trench, we have boring equipment to do it.”

On most of its projects, Innis said, Baker chooses what method of construction to use for burying conduit or cable.

“We base that decision on what is most cost-effective, and if it’s directional drilling, we have the equipment and trained personnel to do it ourselves,” he said.

Baker is the electrical contractor for the new Iowa Events Center in Des Moines, which includes a 17,170-seat arena. The company used directional drilling to install conduit for power cable going to different areas in the complex, including primary conduits, parking-lot lighting and traffic signals. Excavation was impractical because of paved surface improvements and many existing buried utilities. Approximately 4,000 feet of 2- to 4-inch HDPE conduit was installed for power cable. More than 30 bores were made, ranging in length from 50 to 300 feet. Average depth of directionally drilled installations was four feet, under existing utilities.

This past spring, Baker drilling equipment was used to install two 2-inch diameter, 40,000-foot-long HDPE ducts at a new Wells Fargo Home Mortgage office complex in West Des Moines. The duct holds fiber optic cable for communications and high-speed data communications systems between the facility’s headquarters and a new office building. The installation provides system redundancy. Innis said directional drilling was employed because of landscaping on the commercial and residential properties along the cable route.

The decision to purchase the first HDD unit was based on the company’s perspective that it would add a valuable service to its capabilities.

“Once we had the equipment, we actively pursued projects on which directional drilling could be used, and other markets evolved,” Innis said. “We were especially interested in the traffic-signal market, because of the amount of underground work involved, and we had electricians that could perform the complete installation.”

As HDD workloads increased, Baker created a division within the company responsible for directional drilling. Some contractors prefer to subcontract HDD portions of their jobs.

“From a contractor’s standpoint, operating its own directional-drilling equipment is an advantage,” Innis said. “We do subcontract work when workloads are heavy or an installation requires equipment larger than our biggest unit.”

Most commercial jobs will need to have some conduit buried, Innis said.

“When we need to make bores on larger underground projects, we basically wholesale the work to ourselves, and that helps us be more competitive,” he said. “Having our boring division gives us control of when the work is done and by doing it ourselves, we know it is done properly.”

The majority of Baker’s drilling services are restricted to its own projects.

“We don’t seek work from other contractors,” said Innis. “And we’ve found electrical contractors are not interested in subbing work to other electrical contractors—they prefer to call drilling specialists.”

The “size” of directional-drilling equipment is usually defined by its maximum pullback force: the power it has available to pull product through the pilot hole. Baker’s machines were chosen to accommodate the types of trenchless installations they most often make. Baker’s largest unit has 24,000 pounds of pullback and can routinely make runs of 1,000 feet. The next smaller machine has pullback of 16,000 pounds, and the smallest is a 11,000-pound pullback model. Which machine is used depends on the length of the bore, soil conditions, and the diameter of the material to be installed. All machines are Vermeer Navigator models.

As with most organizations that do directional drilling, Innis said Baker has dedicated crews to operate its drilling units.

“It takes experienced personnel to operate this equipment, and it takes a long time for a crew member to become proficient,” he said. “We have eight people trained to operate our drill units. Each machine requires a two-person crew with the tracker operator designated crew chief.”

From Baker’s experience, the chief benefits of directional drilling are an ability to make underground installations without extensive surface damage, which is costly to restore, and to bury cable and conduit in easements where it is impossible to excavate.

Negatives? Per-foot costs for directional drilling are higher than trenching, excluding restoration expenses and the risk of hitting an unmarked buried utility.

Innis said Baker always “potholes”—physically uncovers buried lines to confirm their exact locations—all utilities crossing the path of a planned bore. To pothole, Baker uses three vacuum excavator units, which make “soft” excavations with high pressure water, reducing the risk of damaging pipe or cable being uncovered.

“Our biggest issue is hitting unmarked utilities that you don’t know are there,” he said. “In our area, sewers and water service drops are never marked, so it would be possible to run a duct right through a sewer line and not know it until later when problems with the sewer are reported.”

Bakers clients that own projects that include directional drilling are power companies; municipalities; other government agencies, including street and highway departments; and private corporations.

Baker was active in telecommunications work during the late 1990s, but those jobs stopped during the recent recession and because of various problems within the telecom industry. Nevertheless, Baker has enough work these days to keep its three drills busy. EC

GRIFFIN, a construction and tools writer from Oklahoma City, can be reached at 405.748.5256 or [email protected]. 


About The Author

GRIFFIN, a construction journalist from Oklahoma City, can be reached at [email protected].





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