Auger boring is one of the oldest forms of trenchless technology. An auger boring machine can install casing ranging from 4 to 72 in. in diameter and up to 600 ft in length. That versatility means auger boring can be used to install everything from a small sewer line placed inside a steel casing up to a large culvert under a highway.
However, what auger boring machines lack is the ability to accurately make steering adjustments while in the ground. Two guided auger boring solutions that addressed this, developed in the 1980s, have continued to expand the capabilities of auger boring machines today.
The first was developed by North American auger boring contractor Bill Malcolm. He engineered a steerable auger boring system called the On-Target Steering (OTS) System. The second was a pilot tube system first used in Germany that soon began appearing on job sites in the United States. Both systems were eventually incorporated into the product offerings of various auger boring machine manufacturers. Today, Vermeer MV Solutions, Inc. is the exclusive distributor of the OTS System and the similar Steerable Rock System (SRS), and multiple auger boring manufacturers offer pilot tube system options.
According to Neville Missen, McLaughlin application engineer for Vermeer MV Solutions, both guided auger boring methods are effective at helping crews stay on line and on grade during an auger boring project. However, having spent decades working as an auger boring contractor himself in Australia and the United States, he believes the Vermeer MV Solutions products are efficient to operate and learn how to use.
“Manufacturers looking for ways to offer contractors a steerable auger boring system quickly embraced pilot tube systems when they were introduced,” said Missen. “I believe that’s because the contractor who invented the OTS System didn’t have as much exposure. However, since McLaughlin began selling the OTS System in 2009, we’re seeing a lot more of this type of guided auger boring systems being used.”
Pilot tube method
A pilot tube system is set up on the same tracks as the auger boring machine that will eventually push the final product into place. Using this method, operators take careful measurements to determine the center of the bore diameter, and then a pilot tube (3 to 4 in. diameter) is pushed through the ground to the exit pit side of the bore. A Theodolite Guidance System and Camera is set up behind the pilot tube system to track the pilot tube’s drill head housing through the soil. Steering adjustments are made by rotating the steering head along the bore process — a similar method used for horizontal directional drilling. Once the pilot tube reaches the exit side, a reamer head is attached to the tubing, and a larger trailing pipe string is used to help maintain the hole integrity while pulling the pilot tube back to the entry side. After that pass is completed, the larger pipe string is welded to the final product (steel casing) being installed. In the exit pit, every piece of the trailing pipe string is removed, one piece at a time.
Some pilot tube manufacturers do offer alternatives to the three-step installation process. But, the ability to use a two-step approach can vary depending on ground conditions and the size of the casing being installed.
OTS System method
With the OTS System and the SRS, the auger boring machine is placed in the entry pit, and a control station is put next to it. A steerable head, matching the size of the casing being installed, is then welded to the first casing, and the first auger section is bolted to the steerable head’s cutter. Four hydraulic lines are then connected from each steering flap on the steerable head to the control station. These lines are connected to the top of the steerable head, and a cover helps protect the connections. A water line is run from the control station’s recirculation tank to the steerable head for real-time accurate grade reading. An optional electrical pitch indicator can also be used in conjunction with the water level indicator.
Line is checked through the casing opening using two LED lights mounted inside the steerable head. Course corrections are made from the control station by hydraulically extending or retracting the steerable head’s flaps. To steer up, the operator needs to open the flap on the bottom. He or she can steer down by extending the top flap, steer to the right by extending the left side flap and steer to the left by opening the right flap. There is no need to pull augers to make course corrections. All adjustments can be made in real-time while installing the casing.
Once the bore is completed, the steerable head is removed on the exit pit side, and a cleanout bit is attached to the end of the auger string to remove any debris from the inside of the casing.
“With the OTS System, there is minimal work required on the exit side,” Missen explained. “The whole process is completed in one pass, helping with labor costs and time on the job.”
He added, “Also, since the final product is installed in one pass, there is less potential for the bore path voids and directional deviation than with other guided boring methods.”
Why choose the OTS System
Jim Robinson, owner of Robinson Underground Contracting, Inc. of Ailsa Craig, Ontario, has been an auger borer for nearly four decades. In that time, he’s been a sounding board for manufacturers developing new equipment, even developing a few innovations of his own along the way. Robinson has used both guided boring methods and prefers the OTS System.
“We’ve rented a pilot tube system in the past for an on-grade sanitary sewer project, and it did a nice job,” Robinson said. “With that said, new pilot tube systems are priced quite a bit more than the OTS System. With the OTS System, we can install a casing in line and on grade in one pass with a smaller crew. And, there tends to be less upfront planning involved.”
Robison says that from his experience OTS System tends to have less deviation at longer distances. “I tell people to think about pushing a casing through the ground is like extending a tape measurer through the air — you can only go so far before it follows gravity,” he explained. “However, with a pilot tube system, a crew can pull it back when it does deviate to get everything back in line and on grade. I think the OTS System is less likely to deviate because you’re pushing a larger diameter casing through the ground in the first place.”
Making the grade
Both the McLaughlin OTS System and pilot tube system give contractors a solution for making steering adjustments on auger boring jobs. And, with trenchless installation methods on the rise, usage of both methods will continue to grow.
Dave Gasmovic is business development manager for McLaughlin, a Vermeer brand.