Boring Through Bedrock

Contractor utilizes horizontal directional drilling to extend sewer service to a historic island residence.
Boring Through Bedrock
Waas staged the directional drill in front of the no parking sign by the hotel and restaurant. (Courtesy of Randy Waas)
Boring Through Bedrock Boring Through Bedrock Boring Through Bedrock Boring Through Bedrock

The four-year Riverwalk and Wildlife Viewing Pier project undertaken by the City of De Pere, Wis., included renovating the unoccupied locktender house and adding public restrooms. The De Pere Lock and Dam are listed in the State Register and National Register of Historic Places.

The house, built on a narrow dike called Government Island, had no septic system. To the east, the lock’s canal separated the building from Voyageur Park on the mainland, and the sanitary sewer 50 feet away in a major thoroughfare. The Lower Fox River flowed past the west side of the island and over the dam.

The only way to connect the lavatories to the sewer was to use horizontal directional drilling. General contractor Feaker & Sons Construction in Green Bay, Wis., subcontracted Waas Boring and Cable in Lomira, Wis., to drill under the river and through its limestone bed.

While wind, snow and temperatures in the teens and low 20s slowed the installation, it went as planned. The house received its first visitors during the project’s grand opening celebration in May.

Over the river

The city had ferried equipment to the island with a barge and was preparing to pull it out before the river froze. Feaker workers loaded a spool of tracer wire, a spool with 500 feet of 1.25-inch DR9 HDPE tubing, and an excavator on the barge, then journeyed across the canal. After offloading the cargo, they dug a 10- by 6-foot-wide exit pit 8 feet deep at the back of the locktender house. As soon as the machine was back on the mainland, the barge left.

A restaurant, hotel, and other structures along James Street prevented vice president Randy Waas and his four workers from setting up the D100x120 Series II Navigator directional drill (Vermeer) directly across the canal from the house. “The closest we could get and still keep one lane open was an area just before the restaurant where traffic turned in off Front Street,” says Waas. “Boring on an angle added considerable distance and another day to the job.”

Staging the remaining equipment took up one lane of Front Street. Jammed together were a trailer-mounted, twin tank MCM-4000 reclaimer (American Augers), twin mud mixer and trailer-mounted vacuum excavator (Vermeer) and two flatbed trucks, each with 50 50-pound bags of bentonite.

The team’s biggest challenge was locating utilities, communication lines and laterals from the hotel and restaurant. “The owner of the establishment wasn’t sure where the clean-outs were, and they were hard to find buried under the snow,” says Waas.

Using the vacuum excavator with 1,200-gallon spoils tank and 5.5 gpm/3,500 psi water pump, the crew potholed to expose and verify the laterals and other lines. When all were located, Feaker used his excavator with a frost hook to break through 36 inches of frozen soil and dig the 5- by 6-feet-wide bore hole 4 feet deep. The preparatory work took three days.

Mud matters

“When drilling horizontally through rock, the pitch can change only 3 to 4 percent,” says Waas. “To achieve that, we bored into the rock at 15 percent pitch and were 12 feet deep through the limestone bed before leveling off and boring 350 feet to the exit pit.” A stake with an orange flag driven into a snowbank marked the pit and served as a target for drill operator Eddy Feught.

Boring required an 8-inch rock bit with three rotating carbide bits attached to a 20-foot mud motor (progressive cavity positive-displacement pump). “The diameter seems like overkill for a 1.25-inch waste line, but if we went any smaller, the bits wouldn’t withstand the pressure and difficulty of drilling through rock,” says Waas.

Workers added bentonite and water to the mud mixer, then pumped the drill fluid at 140 to 150 gpm through the drill pipe to rotate the mud motor. As the drill material returned to the bore pit in front of the machine, it was pumped to the reclaimer, which filtered fines from the bore and recycled the fluid.

“The reclaimer has two screens, each with a shaker that distributes debris to the side for disposal,” says Waas. “The important thing is to add more bentonite when the mixture thins out, and that depends on the density of the rock.” The bore averaged 30 feet per hour and took a day.

When the wind blows free

The cold and heavy clothing made work arduous and slow. A tarp enclosing most of the boring machine’s operator station sheltered Feught from the wind, while a Torpedo heater at his feet blew warm air.

“Unless it’s below zero, we can drill,” says Waas. “The men dress for the cold and are acclimated to winter. As long as the pumps keep circulating the drill fluid, it won’t freeze.”

Atlas Bore Planner software (Vermeer) projected a map on a computer monitor delineating the path Feught would follow. To ensure that the bore maintained pitch across the canal, Eric Feught used a DigiTrak Eclipse locator (Digital Control) to track the sonde on the mud motor. Being an avid ice fisherman, he tested the thickness of his footing with a probe before marking the sonde’s location in pink paint. The ice averaged 12 inches thick.

The 12-hour bore used 1,250 pounds of bentonite. After replacing the mud motor with a pulling head, draining fluid from all the equipment and adding antifreeze, the team climbed into the truck with crew cab for the 75-minute ride back to the shop. “Working in the snow didn’t bother us,” says Waas. “The most difficult part was the long drive back and forth in darkness on heavily traveled sloppy or icy roads.”

Pullback

Beginning at 7 a.m. the next day, Eddy Feught began pulling back 400 feet of tubing, which took several hours. On the island, Tim Stieve fed the tubing into the exit pit as two others unrolled it from the spool and worked out the kinks. While Feught pulled in the mandatory tracer wire, Feaker ran the tubing into the house and connected it to a grinder pump, installed by a company representative. “Our job was done,” says Waas. “We washed the equipment, added antifreeze, loaded everything and moved out.”

Feaker excavated 20 feet south from the bore pit, set a manhole at the junction of James Street and Front Street and tied in the tubing. They excavated 30 feet to the sanitary sewer in Front Street and ran a 4-inch gravity lateral to it from the manhole. After backfilling everything with concrete slurry, they laid temporary asphalt for the winter.



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