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Pulling Augers No Longer Needed

by: Neville Missen, Applications Engineer, McLaughlin Boring Systems
One of the most time-consuming tasks while auger boring is pulling augers to check line and grade and adjust steering constantly,” said Walter Keyes, a 25-years auger boring veteran and Team Leader/Superintendent with S.J. Louis Companies. “Typically, on large-diameter sewer jobs, crews will pull augers every 20 feet, which can take a better part of the day when bore distances reach several hundred feet. The process isn’t quick, and honestly, the work can get a little tedious. In fact, on many jobs, a crew can spend around the same amount of time pulling augers as they do actually doing the bore.”

Performing large-diameter bores on-target and on-grade is challenging in normal soil conditions, but concerns about bore path deviation increase substantially in rocky soils where the material density isn’t consistent. Those conditions are precisely what the S.J. Louis auger bore and tunneling team faced on a recent sewer replacement project just outside of Cincinnati, Ohio, in Elsmere, Kentucky.

Working Around Different Issues
The SD1 Elsmere corridor sewer project called for the replacement of 5,900 feet of 12-inch and 10-inch sewer lines that have been in the ground since 1973 with 24-inch line with 36-inch steel casings. While the majority of the work was open cut, auger boring was employed to cross under two busy roadways, a railroad track, and near a creek. The project’s general contractor, Welsh Excavation, handled the open-cut work, and called upon Rockville, Minnesota-based large underground utility sewer specialists, S.J. Louis to manage the four difficult auger bores.

According to S.J. Louis Senior Project Manager/General Manager Bob Schueller, the company has specialized at performing large-sized utility work since 1983. “Our primary focus is open-cut installation work, but we also perform a lot of tunneling, guided auger boring and microtunneling work,” explained Schueller. “We’ve performed tunneling work up to 132 inches in diameter and completed auger bores in varying ground conditions across the nation. Our skilled tunneling and auger boring team compliments our open-cut organization, in addition to our sister company, Atlas Trenchless, which performs large-diameter horizontal directional drilling work. We have always believed in developing and investing in highly skilled personnel that helps us become more efficient so we can stay competitive in our bids nationwide.”

Project Planning
Before work even began, the expertise of the S.J. Louis team was apparent. Geotechnical reports for the soil conditions around the Elsmere corridor included a mix of shale and limestone up to 8,000 psi in density. Given the designed lengths, keeping the bore on line and grade in the consolidated formations would be challenging without the right equipment.

Keyes; Karl Holthaus, S.J. Louis’ Equipment Manager; and Wayne Brown, Tunneling General Superintendent got together to determine the most efficient way to deal with the varying rock formations and came up with a solution.

“At first, we thought we would just use an auger boring machine with a traditional rock disc cutting head,” said Holthaus. “The particular head we had in mind was something we’ve used before, and while we knew it would be able to cut through the rock, the methods to steer and maintain line and grade would have been time-consuming. Using that head would require pulling augers out of the casing frequently to make adjustments. We needed to find a more efficient and less tedious way to complete the project.”

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The team decided to take a trip to Greenville, South Carolina, to check out a new rock steering system that McLaughlin Group, Inc. recently introduced. “We have often used the McLaughlin On-Target steering system in softer soils and have had a lot of success with this product,” said Brown. “The system we were checking out on that day was similar but designed specifically for rock – it was exactly what we were looking for.”

After weighing their options, the auger boring team decided to use a 72-inch auger boring machine paired with the McLaughlin steerable rock system (SRS), which included a 36-inch steerable head and a self-contained control station that gave them the ability to make remote steering adjustments and provide lubrication. “The SRS was a larger upfront investment compared to any alternative options we had discussed, but the potential time we could save in labor and the amount of times the crew would have to handle the augers more than made up for that,” said Holthaus.

First Bore
The S.J. Louis crew put its new rock boring solution to work on the sewer installation project. The first bore they performed was under a roadway and through a hill at a distance of 594 feet with seamy rock formations ranging from soft shale to dense limestone.

“Steering a steel casing through limestone is hard, but a mixture of shale and limestone with varying densities proved to be even more challenging,” said Keyes. “The shale sat above the limestone, so the casing wanted to follow the path of least resistance, which meant we had to pay extra attention to our line and grade and make minor steering adjustments with the steering windows on the McLaughlin head to keep tracking where we wanted it. Rather than having to pull augers after every section of casing we bored, we would monitor the LED lights on the head and the control station’s water level to ensure we were on target right to left and vertically.”

Overall, the team said the first bore went smoothly for never having used the SRS before. The crew did not have to pull the augers to check line and grade for the duration of the bore, Due to the length of the bore, the crew had to pull the augers one time because of an issue with an auger connection bolt from the torque created from the long length of the bore. Even with that unexpected issue, the crew managed to achieve daily productions up to and in excess of 40 feet per day.

Second Bore
The second bore the crew performed was 470 feet near a creek, and the ground conditions were similar to the first bore. The crew completed the whole shot without having to trip out at all and achieved daily productions up to and in excess of 60 feet per day.

“I think it was in the middle of that second bore that I realized this system was the best auger boring accessory that I’ve used in my 25 years of doing this kind of work,” explained Keyes. “It’s not just the production rates either. As those augers work their way through the ground, the rock can leave the metal edges on the auger jagged. The ability to do a whole bore in one pass helps reduce the repetitive task of pulling augers and inserting them back into the casing.”

Another reason Keyes was impressed with this method of boring in rock is that the crew always knew where they were. “On long bores steering is a big deal, because if small adjustments aren’t made properly early on in a bore, it can lead to a bore being significantly off course near the end. With the McLaughlin SRS, feedback is instant and I was confident that we were on line and on grade the whole time.”

Third and Fourth Bores
Production rates were maintained on the last two bores, as well. The third bore was under a railroad track at a distance of 483 feet, and the fourth was 100 feet under a road. At the end of the third bore, the ground conditions went from rock to clay. Some clay did get lodged in the head’s cutter discs, and the crew had to dig down to the head to mitigate the issue. Even with that delay, the team completed all of the bores well ahead of schedule. Keyes estimates that they completed the project in half the time it would have taken with a non-remote steerable rock head.
Next Up
The time saved on the Elsmere Corridor sewer replacement project allowed the auger boring crew to get to work on other projects sooner, which is a good thing for S.J. Louis’s customers. The company’s talented team is busy with projects all over the country, including several large-diameter sewer and water projects in Wisconsin.

“We’ve always said investing in quality equipment will help our crews be more efficient on the job and help grow our business long term,” said Schueller. “The SRS system has proven to be a great addition to our fleet and one we’ll use on many future projects.”

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