May 14, 2014The importance of line and grade accuracy in a boring project cannot be understated. And the maze of existing underground utility lines requires contractors to have precision-like bores every time in order to prevent an accidental hit, resulting in project delays and overrun costs.
The case of a guided boring project near Toledo, Ohio, necessitated pinpoint precision by the contractor in order for the product pipe to clear existing utilities in its path. And it also opened the door for the contractor to expand its trenchless toolbox for future endeavors. The project propelled Turn-Key Tunneling Inc. to use pilot-tube boring technology for the first time in order for four bores to steer clear of existing utility and fiber-optic lines.
The Ohio Department of Transportation (ODOT) was in the process of constructing a new interchange at Wales Road and I-75 outside of Toledo to accommodate growth in the area for manufacturing and distribution. Columbus-based Turn-Key Tunneling Inc. was brought into the project to deal with the underground work associated with what was going on aboveground — specifically installing parallel 72-in. steel casings and two parallel 30-in. steel casings to house carrier pipes for the storm sewer. Each bore was 144 ft in length.
Turn-Key Tunneling was founded in 2005, focusing on auger boring and tunneling projects that usually involve long and grade critical sewer installations, some up to 16 ft in diameter. Turn-Key Tunneling has 11 different auger boring machines in its fleet, ranging from 24 to 72 in. They were purchased from various Ohio-based companies such as Bor-It Mfg., American Augers and Michael Byrne.
This contractor is no stranger to challenging and unique projects; in fact, it welcomes them. The Wales Road Interchange Project proved to fit into that mold.
The ProjectThe culverts to be installed — which occurred between June and August 2013 — were to be constructed under two different sets of railroad tracks, owned by CSX and Norfolk Southern railroad companies. The idea of installing the culverts seemed uncomplicated enough on first review but project site logistics, unforeseen obstructions and using unfamiliar trenchless technology made the project more complex that initially planned.
ODOT was on board with using trenchless technology as a method of installation — however, which trenchless method was best suited for the conditions changed as planning moved forward. The project was originally spec’d out for using the jack-and-bore method but Turn-Key Tunneling had another trenchless method in mind.
“We were going to do the project with a standard auger boring procedure,” Turn-Key Tunneling vice president Brian Froehlich said. “That’s how we initially looked at the project. Once we got onsite, we uncovered existing utility lines, including fiber-optic lines that showed us they weren’t going to clear our 72-in. casing under the CSX tracks.”
An innovative solution was needed. Froehlich and his crew had to design another way to install the casing, with the least amount of disruption to the railroad site. First, ODOT decided to downsize the casing from 72 to 60 in. to allow for an acceptable clearance space — but even that was only by 2 or 3 in. Still pretty risky to auger bore the casing with such a tight tolerance.
Given the aboveground tight surroundings of the jobsite and the minuscule clearance underground, Froehlich decided to change plans to use auger boring and his normal steering system to install the casing. Instead, he turned to pilot tube guide boring in order to increase the quality, line and grade accuracy of the installations — technology the contractor had never used before.
“Using pilot tube technology we could laser guide the bore instead of using our normal steering, which would have been impossible to control within 2 in. on a 144-ft long bore,” Froehlich said.
Froehlich contacted Dave Crandall at ICON Tunneling System to see what equipment the manufacturer offered that could do the job. Crandall recommended ICON’s Model BM400 Pilot Tube Machine. Using the laser guided technology of the pilot tube machine, the Turn-Key Tunneling crew could more accurately guide the casings under the tracks and clear the existing utilities.
“That guided bore keeps it on line and grade so it follows it across, clearing a path for the casing,” Froehlich said.
The pilot tube guided boring machine bores a 5-in. pilot bore, which would be problematic to upgrade straight to a 60-in. hole. ICON’s team recommended that Turn-Key Tunneling upgrade the lines first to 30 in. and then to the final 60 in. ICON also supplied and fabricated the steel adaptors for transitioning from pilot rods to the 30-in. casing and then to the final 60-in. casing.
“The final steel casing was installed only inches from the existing utility and fiber-optic lines,” Froehlich said.
The two parallel 60-in. casings were only 10 ft apart but instead of using just one set up, Turn-Key elected to completely tear down the first set up and move it over 10 ft to do the second 60-in. casing. “It was possible to do it from the same hole but would have resulted in a huge excavation and shoring costs.”
The installation of the two parallel 30-in. steel casings under the Norfolk Southern tracks was successful, as well.
ChallengesBeyond using a method they never used before, other challenges arose during the project, including unplanned for obstructions.
“There were definitely some challenges. We hit some obstructions that nobody knew were there or had just forgotten about,” Froehlich said. “There was a geotechnical report done by ODOT before the project and it did not indicate any issues whatsoever. It proved not to be consistent with what we found.”
Among the obstructions Turn-Key Tunneling ran into was the foundation for an arm of one of the railroad signals, forcing crews to uncover it and then re-route the bore. Another obstruction was a 6-ft by 6-ft concrete catch basin, which had to be dug up and removed before the pilot tube bore could go through.
“We were running the pilot bore and then we just hit something pretty hard,” Froehlich said. “We had shut everything down to figure out what it was. We went back to look at old drawings and maps and finally discovered that a catch basin was there that was part of the existing infrastructure that was being upgraded.”
A different kind of challenge was working with the railroad companies, as well as the fiber-optic company. Diplomacy best described that aspect of the project. “We had to get them all to work together and cooperate on what we were going to do and how we were going to do it,” he said. “Everyone wanted to make sure their interests were protected. The railroad didn’t care about anything other than the railroad and the fiber-optic company didn’t care about anything other than their fiber-optic lines. But at the end of the day, everything came off without a hitch.”
Froehlich is more than pleased with the results of using his first pilot tube guided boring machine, as well as how his team responded to using the new equipment. “ODOT understood the challenges of this project and were onboard with this route we took. Using this technology was the only solution to how the project was designed. The only way to get it built,” he said. “The tight tolerance basically changed the whole game. To be within 1in. is a big deal.”
The use of the pilot tube technology proved to be an asset to getting the project done. “We were not familiar with the guided boring system before this project and we were very cautious in trying it. We thank Dave Crandall with ICON who worked with us and explained teh process and technology. Once we went over it with Dave and his project team, they got our comfort level to where we were ready to tunnel it,” Froehlich said.
Initially the contractor had rented the machine but after the project was over, decided to permanently add it to its fleet of machines — since using it on another job in Jackson, Tenn.
Sharon M. Bueno is managing editor for Trenchless Technology.