August 25, 2015Horizontal directional drilling (HDD) technology has advanced dramatically in the past two decades. Projects once considered impossible are completed routinely, and acceptance of HDD by design engineers and project owners has reached levels where HDD often is the preferred method of construction, even in conditions where excavation is an option.
Horizontal directional drilling may have become commonplace, but some projects stand out from the hundreds being done each year — those that generate special note includes those that are long, deep bores to pull back large-diameter product. Long water crossings are among the most interesting, attention-getting and talked about projects that are done in the industry.
Michels Pipeline Construction recently completed a 2,350-ft-long bore under the Milk River in Montana to install 12-in. diameter steel gas line to replace an older segment of pipe. The bore path was 35 ft beneath the river bottom and parallel to an existing pipeline.
“There was ample room to set up the drill rig to launch the pilot bore, weld the pipe and plenty of work space at the exit end, also,” said Rob Healy, Michels senior project manager. “Width of the river at the crossing was 80 ft. The length of the bore was determined by distance needed to achieve the required depth to go under the river and come up to the exit point. Minimum radius of the bore path was 1,200 ft.”
Healy described subsurface conditions as “difficult,” composed of sandstone and clay stone.
“We used a 6-3/4-in. tri-cone bit for the pilot hole and used walkover tracking equipment,” said Healy. “We did not need a boat for tracking — we were able to locate by wading into the river.”
The first pass was made with a 16-in. tri-cone reamer and the second pass was made with a 20-inch hole opener. Pullback was complete in one day.
A Ditch Witch JT100 All Terrain (AT) model drill rig was used, powered by a 268-hp diesel engine. In addition to 100,000 lbs of pullback, the machine develops 12,000 ft-lbs of rotary torque.
Ditch Witch AT equipment uses a mechanical, dual-pipe drilling system with an inner rod to drive a rock bit and an outer pipe to steer the downhole housing and to provide rotary torque for the hole opener during backreaming. The system delivers maximum available power to the downhole tool for drilling through solid rock, fractured rock, and mixed soil conditions. Because the drilling system is mechanical, AT equipment requires no more drilling fluid than conventional equipment.
“The primary challenge to this crossing was the tough soil conditions,” concluded Healy. “From set up to demobilization, the project was completed in 26 days.”
Michels Pipeline Construction is a diversified pipeline construction contractor with the experience, expertise, personnel, and equipment to perform every phase of pipeline construction. It is a division of the Michels Corp. which provides construction, engineering and procurement services for the energy, transportation, telecommunications and utility construction industries. Michels is based in Brownsville, Wis. Michels offers a wide range of HDD services with an industry leading fleet of equipment and experienced personnel.
Ditch Witch, a Charles Machine Works Co., invented the underground utility construction industry, and today it designs, manufactures and markets a complete line of directional drills, drill pipe, HDD tooling, vacuum excavators, trenchers, chain, teeth and sprockets, mini-skid steers and vibratory plows. Handcrafted in the United States, its products are supported by the Ditch Witch dealer network with more than 175 locations worldwide.
Established in 1902, Charles Machine Works, an employee-owned company, founded in Perry, Oklahoma, is the only manufacturer and global distributor that solely exists to make underground utility construction profitable. Its family of brands includes Ditch Witch, Subsite Electronics, DW/TXS, HammerHead, Radius HDD, American Augers, Trencor and MTI Equipment.