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Pneumatic Boring Head

Aids in HDD Installation Through Wisconsin Limestone
When traveling through the Mississippi River Valley of La Crosse, Wis., the challenges of construction work are quite evident. The towering, tree lined and rock-laden bluffs that surround the Mississippi, Black and La Crosse rivers are beautiful, yet intimidating, to anyone having to complete a project in the area.

In the summer of 2010, Ellingson Companies — which specializes in agricultural drainage, directional drilling, cured-in-place pipe repair and a wide variety of trenchless technologies  — partnered with the City of La Crosse on a challenging water main installation project. The main will supply water to a soon-to-be constructed, 150,000-gal, reinforced-concrete storage tank, located on the crest of one of the many bluffs on the western outskirts of the City.

Ellingson’s crews were lined up to perform a difficult project in the historically significant Mormon Coulee area of La Crosse and the low impact, environmentally sensitive, installation technique of horizontal directional drilling (HDD) was the key to their efforts.

“We knew we were going to have to drill through limestone and that we would face numerous other
challenges stemming from the site location,” said Jason Gillard, Ellingson Companies trenchless division manager. “We were excited to face those challenges and work on such a unique project.”

Site access proved problematic throughout the job, as the site was located in the bluffs, just outside the City of La Crosse. Ellingson’s crews had to transport equipment and materials along old logging roads and through farm fields along the bluff edge where weather played a huge role in access to the site. Despite multiple days of heavy rain, Ellingson Companies completed the project in nine work days, well within the scheduled timeframe for project completion.

Ellingson Companies installed approximately 1,100 lf of 12-in. HDPE in two separate bores through a wide variety of unique soil conditions, including limestone that had a compressive strength of 9,500 lbs. The crew, headed by Ellingson Companies trenchless superintendent Mark Milton, used a pneumatic HDD boring head powered by high-volume air pressure to drill the pilot hole. The technique used by Ellingson Companies was environmentally friendly, as it used little to no bore gel, which contributed to overall waste reduction during the installation process.

The pneumatic boring head is known as a down-the-hole percussive hammer and allowed the crew to drill with power and speed utilizing their Ditch Witch JT100. Down-the-hole percussive hammers, introduced approximately three years ago, force the drill bit into rock at 2,000 blows per minute, and are gaining popularity for drilling water wells, gas exploration, surface mining and blast hole drilling.

During drill-out, the drill head was steered to the proper grade and kept on the predetermined installation path. After the 6 ¼-in. pilot hole was completed, rock reamers were used to open the pilot hole to the required size to pull the pipe. The first pre-ream pass opened the hole to 12 in. and the second pre-ream pass opened the hole to 18 in. In the end, the down-the-hole percussive hammer allowed Ellingson Companies to install pipe, through HDD, in an area that would have been inaccessible to traditional installation methods.

Drilling through the limestone did not come without difficulty for equipment and crew. Ellingson Companies needed to protect the drill and the crew from flying debris coming from the pneumatic boring head. With a safety first attitude, every Ellingson employee made sure all possible steps were taken to keep the job running efficiently and as safe as possible. Equipment was also checked regularly for any possible damage caused by drilling through the rock.

limestone The rock was not the only difficulty faced by the Ellingson crew; having to set the JT100 drill up at 58 percent grade proved challenging as well. “With two bores more than 500 ft long that had elevation changes of 150 ft from the drill site to the bottom of the coulee, it was important that we planned our drill path appropriately,” said Ellingson drill crew foreman Cole Clapp. “The soil conditions were always changing as well. You would start in rock, transition into clay and the next thing you know you’re back in rock.”
“Our guys did a great job under difficult conditions,” said Milton. “They rallied around the project and we were able to complete the project on time, on budget and without inconveniencing local residents.”

After the pipe was installed, crews spent two days completing connections including a hydrant on each end of the pipe and tying into the existing 12-in. city water line. Ellingson Companies completed pressure testing on July 19, 2010, and the water main is available to supply water to the reservoir as soon as the storage tank is complete.

Michael S. Schnell coordinates marketing and government affairs for Ellingson Companies. Courtesy
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