Auger boring continues to fill important niche.(Productivity = Better Bottom Line)
Published in: Underground Construction
Date: 5/1/2006
By: Jeff Griffin
Auger boring is perceived by many in the underground construction business as an effective but old-fashioned method of making short bores to install large-diameter pipe under highways, railroad tracks and other surface obstructions.
For the most part. this viewpoint is accurate. Indeed. auger boring predates the newer trenchless technologies of directional drilling, pipebursting and other innovative trenchless methods. Though there have been significant improvements, the essential components of an auger boring system are basically the same as they have been for years, and the procedure for making a bore is relatively simple and straightforward.
A powerful hydraulic boring unit, usually operated from an entry pit, bores through the earth installing sections of pipe as it progresses. Auger boring equipment is capable of cutting through extremely hard rock formations. Rotating augers carry spoil out of the hole. Installations often are of large diameter casing in which smaller carrier pipe is placed. If necessary, spacers can be used to maintain the carrier pipe’s grade, so small deviations in bore grade are not significant.
However, auger boring has evolved significantly over the last several years. Today’s auger boring equipment is more efficient and productive, is able to make extremely accurate on-grade installations and can cut through tougher soil conditions. These and other factors are allowing auger boring contractors to increase the length of installations.
The average length of auger bores typically has been in the 150- to 350-foot range, notes Gaylord Richey, territory manager for Astec Underground’s American Augers division.
“The power of the auger boring machines being built today–250 horsepower, more than one million pounds of thrust, larger hex drives and improved methods of steering–allow auger boring contractors to take on jobs of 300 to 600 feet,” says Richey. “The record length we are aware of is 900 feet. Could that distance be achieved again? With an experienced contractor, the right machine and careful preplanning, definitely yes.”
David Barbera, vice president of Barbco, estimates average lengths of auger bored installations has reached a maximum of 400 feet and are continuing to increase.
“Newer auger boring units are being manufactured in ways to reduce job-site downtime,” he explains. “Features like rapid travel systems (RTS) help speed up operations while disengaged from the casing. Other features like casing support bars and special saddles assist in the rigging of the next casing for welding. But the most productivity is achieved by the utilization of integrated steering systems or the compatibility of the use of other industry related steering systems such as pilot tube guidance methods. These features help operators hit the target the first time.”
Diameters growing too
Maximum diameters of pipe that can be installed by auger boring also have increased, although they vary greatly with equipment and soil conditions, and estimates of pipe sizes being installed today vary widely–outside diameters from 12 inches on the small end to as large as 72 inches.
Richey says the most visible feature that increases productivity of newer models is the ability to quickly return the machine back to the base track after pushing a section of pipe in the ground.
“The new quick track feature that utilizes a rack-and-pinion design, similar to that used on horizontal directional drilling (HDD) machines, engages two pinions (one on each side of machine) into a gear rack,” Richey explains. “Each pinion is powered by a hydraulic motor and can move the machine from front to rear of the track in approximately 30 seconds. This feature not only speeds up the time on the return trips during the augering process; it also reduces the amount of time to trip out augers to check line and grade, to remove augers and steering rods upon completion of the bore, and to push product into the casing. This significantly increases contractor productivity and profitability.”
Highly-accurate steerability is another feature that sets current auger boring equipment apart from earlier models.
For many years, monitoring a water level was used by operators to adjust grade of a bore. Today, machines use electronic and laser equipment to control both line and grade (the May 2005 issue of Underground Construction covered this topic in detail). The ability to make longer bores with greater accuracy control has been a factor in expanding demand for auger boring.
Small diameter impacts
While introduction and growth of directional drilling and other trenchless utility construction methods have impacted auger boring, most in the industry agree that the demand for it has remained remarkably stable as applications shift and in some instances expand.
“The number of small-diameter auger boring machines (ABMs) produced for 4- to 10-inch diameter pipes to make short 50- to 100-foot installations have declined with the introduction of compact HDD machines,” Richey says. “The time and labor saved by not having to dig an entry and exit pit, plus restoration, makes the mini HDDs more cost effective for these size installations.”
However, Richey says for installing pipes of 24 to 48 inches in diameter to distances of 100 feet and longer, auger boring is very cost effective, and demand for auger boring remains constant.
“In these sizes,” he continues, “equipment and mobilization costs can make HDD cost prohibitive. And with population growth on the rise in the U.S., utility companies are forced to increase product pipe sizes to meet current demands and prepare for future growth. In addition, for the first time we are seeing an increase in auger boring in the international market due to all the infrastructure work taking place in certain areas to construct modern water and sewer systems.”
Overall, Richey says the number of specialist auger boring contractors remains stable. He adds: “We see more contractors adding ABMs to their fleets, not to become boring specialists or to make auger boring their primary source of work, but to do the limited number of bores they require with their own crews.”
As with other trenchless procedures, limiting the amount of excavation and being able to make installations where open-cut construction is impossible is the primary reason for undertaking boring on many project segments. Traffic disruptions are minimized, and reducing the amount of excavation saves additional time and money by limiting the amount of surface restoration required after pipe installation is complete.
Casing
Richey notes auger boring is widely used to install casings in which conduit, sewer, water or gas pipe is placed. In addition to highways and railroads, airport projects take advantage of the technology.
“Air traffic has increased which is forcing airports to expand,” he continues. “The paperwork trail alone just to shut down a runway for a period of time would be mind boggling in addition to very costly.”
To achieve maximum productivity Barbera and Richey emphasize the importance of planning, proper set up and operation of equipment in accordance with manufacturers’ recommendations.
“Use the right size machine for the job,” says Richey. “The proper cutting head for soil conditions is critical to maximum productivity. Entry pit preparation is crucial to the success of the bore. Make sure the pit width and length are adequate for the size of the machine and casing lengths being installed. To help maintain line and grade, the machine and track should be placed on a surface that will support the machine’s weight and will not sag or settle below the required grade. A concrete bottom is best, timbers and gravel will work.
“Finally, safety is essential. Pits must be properly shielded or shored, and all personnel must adhere to OSHA safety guidelines.”
Auger boring machines may lack the perceived “glamour” of horizontal directional drills, but they continue to be widely used because of the relative low cost of making an auger bored installation compared to other trenchless methods and because there are a large number of contractors with auger boring machines who have the experience to use them effectively.
FOR MORE INFORMATION:
Auger boring machines: McLaughlin, (800) 435-9340, mightymole.com Barbco, (800) 448-8934, barbco.com American Augers, (800) 527-6020, astecunderground.com Bor-It Manufacturing, (419) 289-6639, bor-it.com
Jeff Griffin * Senior Editor