When Trevor Zimmerman and his crew arrived at the job site in Osceola, Wis., he thought things would go just as they had a year before when they completed a similar utility construction project in the area. But what he soon learned is that, "No matter how well you plan, don't be surprised if there are unforeseen circumstances that arise."
Zimmerman, corporate controller for Push Inc., Rice Lake, Wis., helped oversee the installation of an 18-inch sanitary sewer pipe in a new construction residential and commercial area in Osceola.
Push Inc. was hired by the project's general contractor, A-1 Excavating, Bloomer, Wis., to install the sanitary sewer system that will eventually service homes, businesses and a hospital being built in the area.
The $425,000 project involved installing about 1,400 feet of 18-inch sanitary sewer pipe at a 2-percent grade.
Zimmerman said his original concern was the depths that Push Inc. had to drill.
The deepest depth needed was 32 feet, but then they had to exit the bore at 10 feet deep. The total 1,400 feet was to be drilled in several shots. Initially, all of the shots were going to be about 400 feet long.
But when a manhole was eliminated from the project, it took away a midpoint and combined two 400-foot shots into one 765-foot shot.
When Push Inc. began planning how to tackle this project, it was assumed it would go as well as the project they had completed earlier.
"We were basically within about 1,000 yards of the area we had been the previous year," Zimmerman said. "Initial soil borings indicated the same type of rock material, and they were straight shots. Though there was a little bit of a depth problem, we didn't have any problem with locating readings the previous year with our walkover electronics. And we knew we were going to be at least 20 feet shallower than we had been the year before."
So in the beginning, there wasn't a lot of extra planning because it looked like a straightforward job.
Zimmerman said the crew performed a bore plan mainly to determine where their offset and setback needed to be.
"It was a good thing we did because this one quickly turned around on us," said Zimmerman.
Push Inc. crews began the project by tackling the 400-foot-long bore. But as they began drilling they ran into some difficult soil conditions such as sandstone and other rock formations.
Between those harder soil conditions, there were pockets of sand that affected the steering capabilities of the horizontal directional drill (HDD). Another unforeseen obstacle that Zimmerman and his crew faced was an underground river.
"From that point, we started losing our mud and fluid capabilities. However, we did make it work. We were able to pull back that first 400 feet of sanitary sewer pipe," Zimmerman said.
Because they had faced so many obstacles on the first 400 feet they bored, Zimmerman decided to take a different approach with the longest bore.
With the 765-foot stretch going through a hillside, he wanted to drill down from the top of the hill.
"We thought that at the bottom side of the hill we would be at a shallower depth, however, we still needed to be at 32 feet deep at our first manhole at the top of the hill," said Zimmerman.
Knowing they wouldn't be able to bore the entire 765 feet with the HDD machine currently at the job site, they decided to drill out as far as they could while maintaining a 2-percent downgrade.
With a tri-cone drill bit, the crew was able to cut through the hard soil conditions, but problems arose when they got about 15 feet deep.
"We were no longer able to locate our drill head," Zimmerman said. "We could drill it, but we couldn't see it."
That's when the Push Inc. crew began trying all kinds of different options.
They swapped out a competitive HDD machine and drill heads and tried several different locating systems, including a Digital Control Incorporated (DCI) prototype locating system that was able to read up to 22 feet deep before losing its signal.
After doing all of this with no success, Zimmerman said they turned to Vermeer Manufacturing Company and DCI for help.
"We started working with them to come up with the right mud motor and the right wire-line system. That's when Vermeer recommended the NAVIGATOR® D100x120 HDD machine," he said.
Push Inc. owns several HDD machines, including eight Vermeer® NAVIGATOR models. Their smallest Vermeer HDD machine in their fleet is the D7x11a, but they also own several D24x40as, D33x44s and a D50x100a.
Zimmerman and his crew found that the Vermeer D100x120 HDD machine with the setup of a standard mud motor, whose locating point is about 18 feet behind the drill head, solved their locating problem.
So for the remainder of the bore, they used the D100x120 and standard mud motor with rear-load housing and the wire-line locating system. But throughout the entire 765-foot bore, Zimmerman said they had to put their trust in the machinery.
"We went by the premise that pitch doesn't lie. So if it's telling us that the drill head is going down at negative 2 percent, we're believing that's what it's going down at," he said.
Unfortunately, doubt remained about the drill head's lateral deviation and they still needed to use the walkover locating system to help determine if they were going right or left.
To eliminate any further doubt, the crew opted to use the Vermeer ATLAS BORE PLANNER® software to set their perimeters so they could monitor the bore on a per-rod basis.
This way, they always maintained the exact pitch they needed per rod in order to hit their ending point.
"Gradewise we came out perfect. There was a little bit of left and right that we had to try and make up, but we were fairly close. We got through it," said Zimmerman.
Once the bore was drilled, Push Inc. performed three prereams with hole openers in widths of 12 inches, 16 inches and 24 inches.
"The only reason we did that is because it was an 18-inch pipe that we were installing and we had already encountered enough problems on the project that we wanted to make sure we had a nice, smooth, clean hole for an easy pullback," Zimmerman said.
In addition to the prereams, the crew also used a bentonite-based mud-fluid mix.
Push Inc.'s biggest challenge was the soil conditions.
One thing the crew learned was how drastically ground conditions can alter your electronics. Finally, after the bores were complete and they started digging the manholes, the crew discovered the culprits behind their locating problems. At about 10 feet to 14 feet below the surface, they found layers of copper and iron — metals that wreak havoc on electronics.
In all, the entire project took a total of 11 weeks to complete.
At the end of the project, Zimmerman said Push Inc. was so impressed with the Vermeer D100x120 that they plan on adding it to their fleet of HDD machines.
(Editor's Note: The story was written by Tara Deering of Two Rivers Marketing, and provided by Vermeer Manufacturing Company.)