Nothing Dull About Boring
Auger Boring Helps a
Tennessee Company
Complete a Major
Highway Reconstruction Project
By Greg Ehm
“Where tradition meets tomorrow” is the motto of Fayetteville, located in mid-southern Tennessee. It’s also an apt motto for Mid South Utility Contractor, which was contracted to relocate all of the water, sewer and gas lines along a 6-mile stretch of U.S. 64 that passed through Fayetteville. The utility contractor was part of a major, two-year highway reconstruction project in the community of nearly 7,000. And while Mid South Utility Contractor has been auger boring in the area for years, it took a specifically-designed boring machine to cut through the area’s rock with precision.
Flash back to the mid-1980s when the Tennessee Department of Transportation began an initiative to widen this primary east-west route that serves southern Tennessee. The project spanned 10 counties from Memphis to Grundy County’s I-24. In total, more than 266 miles of the highway would be widened to a four-lane route. The goal: Help stimulate growth and economic development in the region.
The project has moved along smoothly for 22 years with the help of residents, community leaders and contractors who know how to deal with the ground conditions. Tennessee is known for its music, food, whiskey and rock. That’s right — Tennessee is full of high-quality limestone.
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The rock system, combined with the 36-42C auger boring machine,
allowed crews to drill forward with the stabilizers, fill the void created
by the pilot head and steady it for an accurate shot. |
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Enter Mike Herren. Herren is the President of Mid South Utility Contractor located in Baxter, Tenn. Herren got his start in the underground business back in 1992, doing odd jobs with his backhoe. In 1993, he got his first break and took over the maintenance work for a local water utility district. This project helped to catapult his business and soon he was installing water, sewer, gas and telecommunications lines throughout the region. Today, Mid South Utility Contractor specializes in the installation of water, sewer and gas lines and is known for its expertise in boring — especially in rock.
While relocating the water, sewer and gas lines on US 64, Herren’s crews installed 2 1/2 miles of sewer, 3 miles of force main sewer, 3 miles of natural gas lines, 2 1/2 miles of waterline and 42 manholes. The project took two years and required Herren to test his boring skills.
“The majority of the lines were open cut, but we had to complete 20 bores ranging from 60 to 120 ft in length under the highway,” says Herren. “The bores accounted for 30 percent of our work on the project.”
The project required Mid South Utility Contractor to install 20-ft sections of steel casings, ranging from 12 to 30 in. in diameter. The water lines were installed under the highway at a depth of 6 to 8 ft, while the sewer lines had to go in at 15 to 20 ft on grade.
“We’ve been auger boring a long time in rock, but not at the precision that we had to be on these gravity sewer lines,” says Herren. “We knew we needed some help and we called McLaughlin. They came in with their rock system and customized it to our project.”
McLaughlin — a manufacturer of trenchless construction equipment, including auger bores and MightyMole moling tools, out of Greensville, S.C., and a NUCA associate member — provided a rock system that was designed specifically for solid rock applications. The system features a pilot head with three roller cones set up to cut 6 1/2 in. on the outside diameter (OD). Behind the pilot head are two 5-ft long stabilizers with ribbing on them to bring them up to the OD of the pilot head.
When drilling forward, the stabilizers fill the void created by the pilot head and steady it for an accurate shot. The pilot head and stabilizers are attached to a drill stem that allows water to flow through to the head, flushing the cuttings and keeping the pilot head cool. Herren used the rock system with his McLaughlin 36-42C auger boring machine.
The sewer bores began by creating and shoring a pit 20 ft deep by 32 ft long. The pit was set 10 ft back from the new road. Once the pit was set, the boring machine was positioned.
“Since you cannot steer the auger, setting up the machine is key,” says Mike Moore, Vice President of Sales for McLaughlin.“It needs to be in a straight line in the direction you want to go and at the grade of the bore. We also had to make sure the machine was square. This takes the most time and the rock will keep you in once you get the machine square.”
Once the pilot head was square, the crew began boring and continued to add drill stem until they reached the other side of the road. When they reached the receiving pit at the other side of the road, they continued to rotate the pilot head forward and began pulling the stem back out of the hole.
“During this process we pumped water from the receiving pit back toward the machine to help flush out any remaining cuttings,” says Moore.
When the pullback was complete, the rib stabilizers and pilot head were left in the hole and a 16- in. reamer head was attached. The reamer head featured a series of roller cones up to the OD. On the back side of the reamer, the crew attached a standard auger and the first 20-ft section of casing. The crew began to ream the hole and continued to pump water from the receiving pits back into the boring machine to keep the head cool and flush the cuttings back into the pit. The 20-ft sections of casing were welded together as the bore progressed.
“The pilot hole is the slowest part of the process,” says Herren. “It takes a couple of days to get the pilot hole completed and a total of four days to complete each bore.”
Once the new main lines were in place, Mid South Utility Contractor began the process of laying new service lines to each home and business along the route. The old lines were in service until all customers were connected to the new lines. The old lines were then abandoned to keep service disruptions to a minimum.
“It was a pretty mean job; I’ll just put it that way,” says Herren. “This project was right in the middle of town among all the homes and factories, so we had limited work space. But the system worked well and helped us successfully complete the project.”
Greg Ehm is a Technical Writer for Two Rivers Marketing, Des Moines, Iowa.
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