Sac Osage Electric Cooperative in El Dorado Springs, Missouri, has been delivering power to primarily rural customers in Missouri for more than 65 years. Small in size with only 37 full-time employees, the cooperative has been an innovator and early adopter of safer, more productive methods and equipment. One of those innovations, from a hometown manufacturer in El Dorado Springs, has changed the way utilities install new poles in rock.
Missouri calls itself the “Show-Me State,” but it is also known as the “Cave State,” with 5500 caves and counting. This speaks volumes about the geology, particularly in the nine counties that Sac Osage serves in south-central Missouri. The Crystal Caves, a national tourist attraction, are only a few counties away from Sac Osage. Marble is also quarried in the region.
The state is divided north and south by the Missouri River and is a bedrock of sedimentary rock. The northern half of the state is covered with a thick blanket of glacial drift over-lying much of the bedrock. In the west-central part of the state, Sac Osage's service territory, the sandstone and limestone are more apparent. Located north of the Ozarks and Branson, two Missouri vacation destinations, the thick, massive bed of dolomites, of Cambrian and Ordovician age, is obvious at road cutouts and next to creeks and rivers.
The Challenges of Rock
Sac Osage pole crews have been dealing with rock conditions ever since the utility began installing poles back in the mid-1940s. At that time, the first power lines were built near Stockton, Missouri. For many years, it was a major challenge applying brute force against the hard rock.
Sac Osage owns three tandem-axle digger trucks with 50-ft booms and 18-ft-reach auger capability. The booms have free play with a tendency to flex under the load of rock drilling. The drill bit itself tends to walk across the hard surfaces instead of digging in, and after the hole is started, the bit is easily deflected from drilling in a straight line. Jamming of the auger bit in the hole also may occur along with broken auger teeth, which must be repaired periodically.
Up until a few years ago, Sac Osage crews used air compressors and jack hammers along with dynamite to get a clean hole in the ground. These are not only time-consuming and dangerous methods, but explosives regulations in recent years have made it prohibitive to keep blasting caps and other highly regulated supplies on hand. If holes need to be blasted, a licensed agent authorized to carry, store and use explosives by the Bureau of Alcohol, Tobacco and Firearms is hired to blast the holes.
Even more challenging is getting a clean hole 16 inches by 6 ft deep. Explosives leave chunks of rock that must be removed from the hole and a less-than cylindrical hole that requires extra backfilling and tamping around the base once the new pole is erected. While a dirt hole can take a crew 20 minutes to bore, rock beds and rocky soils can take four to eight hours.
Heard that Before
All of that changed a few years ago, when Ron Harleman, a local manufacturer of heavy-duty boring tools and equipment, called to tell Sac Osage about a new auger he had designed that would bore rock.
The standard method of drilling utility pole holes in rock is manual. A lineman with a jackhammer typically breaks up the rock, and the rock is removed with a shovel. This method is obviously time consuming, and a single hole may take a day or longer to drill to the required depth. Thus, there is a need in the utility industry for a drilling apparatus that will overcome these problems.
Harleman Manufacturing is known for its foundation anchoring equipment, tree saws and heavy digger equipment. But in El Dorado Springs, Sac Osage was still using dynamite to dig holes for new pole installations. The utility's foreman's first response was, “I've heard that before.” Harleman's, reply was, “You have to see it to believe it.”
Seeing is Believing
With years of experience working in rock, Sac Osage was doubtful of Harleman's claims. The next day, Harleman pulled into the yard with his heavy-duty rock auger and offered to attach it to one of Sac Osage's digger trucks. A linemen's safety meeting was scheduled that day, so the crew decided to demonstrate the auger at a rock quarry near the office in El Dorado Springs. As the crew was preparing for the demonstration at the yard, a call came in from a pole crew installing a new pole west of town. The crew reported that it ran into rock 18 inches down. Normally, this meant a change in the game plan — an air compressor, a rock hammer and dynamite. Harleman said, “Let's drill it.”
With the field operations crew standing by, using only Sac Osage's digger truck with the new heavy-duty rock auger attached, the pole crew drilled the entire 6-ft hole in solid rock in 25 minutes.
The top head of the special auger has a quick connector that bolts on to the Kelly bar on most digger derricks' torque heads. Its most unique component is the single-flighting on the auger and a single-blade cutting head. The tungsten carbide cutting teeth that extend outward at a forward angle from the bottom edge of the cutting head are designed for more aggressive rock penetration.
The ability to bore a clean hole in solid rock in 25 minutes was impressive. Crews told Harleman to “leave it on the truck.” Although the auger has a quick disconnect coupling, Sac Osage now uses the special auger for both dirt and rock boring.
News Spreads Fast
The success of the hometown demonstration has changed the way Sac Osage installs poles. Good news spreads fast, and today, utilities around the world are using the heavy-duty augers. Sac Osage has outfitted all three of its diggers with the auger, which works in both earth and rock. Crews have not had a single bore they couldn't complete with the rock auger, and they have not used dynamite in more than two years.
K. Lee Whitesell is a journeyman lineman and line superintendent for Sac Osage Electric Cooperative, where he has worked for more than 40 years. Sac Osage Electric Cooperative, headquartered in El Dorado Springs, Missouri, provides electric service to about 8500 members on a system that includes more than 2300 miles of line and 10,000 meters.
POLE INSTALLATION IN ROCK
- Digging the Hole
The size and depth of the hole depend on the diameter and height of the pole. A general rule of thumb for setting utility-pole depth is 10% of the nominal length, plus 4 ft. Most of Sac Osage's holes are 16 inches by 6 ft. Assuming the site has been surveyed and properly staked, the auger-excavation procedure using the rock auger is the same as vertical boring in dirt soil. Sac Osage uses dangle-derrick-type digger trucks, which means the weight of the auger and the hydraulic top pressure on the boom are used to pressure the auger into the ground.
Soft rock and round flint tend to drill quickly, but harder limestone requires much more grinding. In rock, the spoils typically auger out around the hole and are drawn away from the hole with a hand shovel. From time to time, the boom operator may pull the auger out of the hole and shake the spoils out of the auger flighting over a tarp next to the hole. They are usually loose and not compactable. The advantage of drilling in rock is the walls of the bore hole usually remain true and undisturbed when the auger is removed.
- Lifting and Handling
A steel choker or a flat nylon strap is used to lift the pole into place. Beyond the normal safety precautions associated with handling the rough exterior of wood poles, crew members wear long-sleeved shirts, long pants and leather gloves that are impervious to the pole treatment chemicals. When they work on energized lines, they also wear rubber gloves and other personal protective equipment. The normal aerial-boom safety precautions are also followed, including having a spotter assist the boom operator during the pole erection.
- Plumbing and Tensioning
To align the pole vertically, crews carry plumb bobs. Once the pole is erect in the hole, the boom operator holds his plumb bob out at arms length and eyes the string against the pole. Another crew member also plumbs the pole from left to right and front to back. While the hole is backfilled with native soil or a compacted aggregate, the hole is intermittently tamped either manually or with an air tamper.