Equipment:
20×22 Vermeer®
36×50 Vermeer®
STRAIGHTLINE® RockEye Air Hammer 4.0 with a 1150 cfm x 350 psi air compressor
The Challenge:
Metro Communications encountered an incredibly challenging bore, which threatened completion of an entire project. The task at hand was to cross the Vermillion River near Interstate 74 and Illinois State Highway 150. The tributary serves as the water supply for a nearby community. Environmental concerns of contamination into the water supply, made the RockEye hammer technology a perfect fit for completing this project.
Set up elevation was 20’ above water level. The plan placed the estimated 600’ bore at 15’ below the streambed before ascending to the extraction point, 40’ above the surface, on a hillside across the river. The ground conditions consisted of shale, shelf rock, and blue clay with 10’ – 12’ of river rock near the water level; the goal was to stay below the rock bed, in the blue clay under the river.
The bore path was chosen to navigate around existing fiber cable attached to a bridge structure. The other major hurdle in this project was navigating through the old bridge supports that remained at unknown depths. The bore was first attempted, without success, using a 20×22 Vermeer® rig and traditional HDD tooling. A 36×50 Vermeer then was set up, and it also was unsuccessful in completing this bore.
The Solution:
Due to a track record of success in similar situations, Craig Bennett, of Metro Communications, called StraightLine® HDD, Inc. to discuss the RockEye hammer. StraightLine deployed Lead Field Engineer, Ron Becker, to complete this challenging job.
The RockEye hammer, coupled with an air compressor operating at a rate of 1150 cfm at 350 psi, passed through 20’ of shale rock at a rate of 1’ per minute. Lack of return air flow hampered the hammer through the coble, however, the speed of progression remained much the same. Air flow again became an issue, as the hammer made its way down-hole through the blue clay. The loss of returns down hole caused pressure to be equalized in and around the hammer and the tool stopped working. Drilling in the blue clay was made impossible, due to air not escaping the air hammer. A heavy bentonite was mixed and pumped through the hammer to bring it back through the river rock formation. The decision was made to use the mud pump on the drill along with the support pack. This enabled the flow of water to run at 10 gallons per minute from the drill, and a water/foam mix to flow from the StraightLine® Support Pac. StraightLine’s® Ron Becker explains, “The Cetco® Versa Foam is a shale stabilizer and it thins, or lightens, the cuttings with the fine air bubbles. This allows the clay to flow back into the river rock formation until we steered up into the coble on the opposite side of the waterway.”
Metro again experienced some drag in the river rock as they climbed the far bank; however, they were able to operate with a small degree of difficulty, before steering up through another 20’ of shale, hitting the exit pit on the other side that was in a sandy loam. StraightLine’s® Ron Becker was only on site two days to complete this challenging bore. Due to the varying soil and complex bore profile, this completion was accomplished in a fraction of the time of prior attempts with conventional tooling. Craig stated, “The speed and precision of the hammer was certainly more than expected. The RockEye hammer system allowed us to complete this project in record time.”