Location:
Climax, Kansas
Equipment:
StraightLine HDD® RockEye 5.0 Hammer System on a Vermeer 60×90, powered by a 900×350 compressor.
The Challenge:
The Nowak Construction crew found themselves in a difficult situation on a recent rock bore. Located in the heart of the Flint Hills region of central Kansas, the job called for the installation of an 8-inch OD water pipe. The 400-foot bore, part of a large rural water pipeline project, passed under Otter Creek, necessitating the implementation of measures to minimize fluid intrusion into the waterway.
The layered rock, comprised of limestone and shale, was manageable. The real challenge, as the Nowak crew soon realized, centered on the broad disparity between rock layers within the bore path, alternating from solid to broken rock, with variations in hardness throughout. The veteran crew knew the inconsistent geology would make steering a major challenge.
Intensifying the steering challenge, the bore path included a quick 40-foot drop at entry and a corresponding 40-foot climb at exit, with a 30-degree turn in the last 150 feet of the bore.
Over the time span of three weeks, a Ditch Witch® 3020AT, using conventional methods, attempted the bore. After four failed shots—attacking the bore from both sides of the creek bank—it was clear the Ditch Witch AT could not engage the varying rock faces.
Nowak Vice President, John Nowak, summed up the situation: “The alternating solid and broken rock—combined with the inconsistency in hardness between layers—made it difficult to control the drill head.”
Nowak realized the use of thrust in conventional drilling was the source of trouble, explaining that “Conventional drilling requires the use of thrust pressure in order to steer and make forward progress. On this shot, when we applied necessary forward pressure, the drill head assembly couldn’t engage the face of the rock when transitioning between layers.”
StraightLine HDD Lead Field Engineer, Ron Becker, had completed a demo bore for Nowak two weeks earlier. The successful demo prompted Nowak to purchase a RockEye 5.0 air hammer system. The system and training was scheduled for the Otter Creek bore.
After spending half of the first day assessing the plan and evaluating conditions, Becker set up Nowak’s RockEye 5-inch hammer. The hammer was configured for a Vermeer 60×90 that the Nowak crew initially planned on using to handle the back ream. Steve Nierman, one of Nowak’s most experienced drill operators, was pegged to handle the hammer shot.
The Outcome:
On a chilly, rain soaked job site, the RockEye 5.0 entered the limestone rock just before noon. With control being of paramount concern, Becker’s plan centered on finesse, rather than force. “In this situation, we had to just let the hammer do all the work,” explained Becker. “It may sound counter-intuitive, but moving between soft, loose rock into harder formations, using light forward pressure allowed the hammer’s bit to grab hold and engage the rock.”
Maintaining the correct angle on the hammer bit was also key. Becker explains: “Even after the right depth was achieved, maintaining 3 to 4 percent steering angle was critical. This allowed the hammer to effectively engage and hold the bore path as it passed from one layer to the next.”
At 2 p.m. on the following day—just 12 hours after entering the tough Flint Hills limestone—the RockEye 5.0 Hammer emerged from the exit pit on the far side of Otter Creek. Hammer operator Neiman reported the light “touch” on the hammer yielded, on average, 15 feet of production per 20 minutes.
Equally impressive was the steering. “We obviously had a lot of challenges in steering on this one,” recalls Neiman. “Throughout the bore—the elevation changes, the big turn at the end and dodging the voids created by the four previous bores, the RockEye was exceptional.”
