Keep The Bore Path On The Straight And Narrow

A New Auger Boring Steering System Helps Georgia Contractor Stay On Course
October 2011, Vol. 66 No. 10

“There was a combination of issues that were concerning as we planned how to best approach the project,” Lewis says. “We knew the boring lengths would push the tolerances of the auger boring approach somewhat, an issue further complicated by the depth that would be required to comply with DOT cover specifications. If that wasn’t enough, there was the sand/gumbo soil profile mix; something we knew would be difficult to predict and correct as we got further along in the progression of each bore.”

Lewis was confident that auger boring was the right method but was also concerned about the incidence of drifting, given the length and depth of the bores. He chose the McLaughlin 42HD auger boring machine, with 42-inch boring capacity. What he didn’t expect was an additional tool he would put to the test after discussing the project with McLaughlin.

“I was expressing some of my concerns to our contacts at McLaughlin and they felt the ON Target steering head would be a great tool for minimizing any drifting issues,” Lewis says. “After discussing it further and learning more about the capabilities of the system, I was more than willing to give it a try.”

Digging deeper
The Georgia Department of Transportation (DOT) requirement dictating six feet of cover forced Lewis to dig the launch pit at 18 feet. The ground conditions at the pit locations were good, so Lewis’ crew only needed to add gravel in the launch pit along with steel plates to solidify the base. A big concern at that depth is the ability to maintain the alignment and grade of the cutting path, not to mention the alternating sand and gumbo mix. Boring through sand requires dewatering, while boring through gumbo requires the presence of fluid to facilitate the spoil removal.

“Boring through a gumbo and sand mix can be tricky because gumbo balls up and free-flowing sand can create voids,” Lewis explains. “We had to be careful to adjust the speed of the bore as the steering head moved from sand to gumbo and back to sand. To further complicate matters, there were several instances where we were boring through a sand/gumbo mix. This made adjusting the boring speed critical.”

After installing each 40-foot section of casing, the crew checked grade using the built-in water level and left/right alignment using the halogen light system. If necessary, adjustments would be made by opening or closing the hydraulic actuated panels of the steering head before installing the next casing segment. In the end, both bores were completed successfully. With the casings firmly secured, Lewis took a moment to reflect on all of those pre-bore concerns.