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Conquering rock

From the time the first horizontal directional drills began installing underground pipe and cable, rock has been a continuing challenge. Ditch Witch considers machinery available to operators that can effectively drill through rock.

The first horizontal drills through rock began around 20 years ago, and during that time Ditch Witch has been recognised as the rock expert, says Randy Rupp, Senior Product Manager for horizontal directional drilling (HDD) and drill pipe at Charles Machine Works, manufacturer of Ditch Witch equipment.

“From special rock bits and downhole tools, to developing special techniques for effectively drilling through rock, Ditch Witch has provided solutions for working in rocky conditions,” Mr Rupp continued.

Enter the All Terrain

The Ditch Witch All Terrain drilling system has expanded the scope of horizontal directional drilling by making it possible for relative compact drilling equipment, designed for utility construction, to complete trenchless installations in rocky conditions.

The patented mechanical dual-pipe All Terrain (AT) system is available today on three Ditch Witch drilling units with pullback capabilities of 30,000, 40,000, and 100,000 pounds.

“An AT machine can effectively bore and steer through rock that is beyond the capabilities of conventional equipment of comparable size and pullback,” said Mr Rupp.

“For project owners, this means that rock does not preclude the use of directional drilling on many projects once considered undrillable. And for contractors, having AT equipment gives them an edge over competitors, allowing them to gain work others are unable to attempt.”

The history of rock and HDD

During the early 1990s, HDD gained acceptance by a growing number of utility owners and operators as an innovative new method of installing underground pipe, duct, and conduit.

However, the compact machines developed for utility work were unable to work effectively through rock, eliminating HDD as an option on many projects. While directional drilling through rock was not uncommon during that time, it required a large, powerful machine using a mud motor – technology adapted from the oil fields. Drilling fluid powers mud motors, and it requires substantial quantities of fluid and support equipment, making their use on typical utility job locations too costly.

In 1995, a Ditch Witch dual-pipe mechanical drilling system was introduced on a machine with 22,500 pounds of pullback, at the time the largest Ditch Witch HDD model.

Working with customers, Ditch Witch engineers refined and improved the dual-pipe system and in 2000, the All Terrain system was introduced on the Jet Trac (JT) 2720 model, a 27,000-pound pullback machine that became widely used for utility construction.

“There were several refinements leading to the “÷All Terrain’ designation,” said

Mr Rupp. “One of the most significant is the AT pipe. Early versions had screw-together inner pipe that required additional steps to connect and disconnect pipe sections, making pipe makeup very time consuming.”

“The drill head has a two-degree bend, and the beacon is directly behind the drill head, not several feet back; ensuring information transmitted to the operator about the bit’s location and position is accurate,” Mr Rupp continued.

Unlike conventional HDD equipment that uses a single drill stem and a slant-face boring head to control steering, AT models use a mechanical, dual-pipe system that delivers maximum downhole horsepower.

An adaptable system

The AT system enables simultaneous drilling and steering through rock and rocky soil. AT equipment requires no more drilling fluid than conventional equipment. In addition to rock, the AT system is effective in dirt and most other soil types.

“If a machine is used mostly for rock and patches of other soil are encountered, a dirt head can be attached and the crew just bores through it,” said Mr Rupp. “If an AT machine is going to be on a large job with little or no rock, AT pipe can be changed out for conventional Jet Trac pipe.”

The effectiveness of the system has brought a growing demand, and the three available models provided a range of sizes and capabilities. The machines have been employed in most types of terrain in rock formations ranging from cobble to solid formations up to 30,000 psi and higher.

Since its establishment, there have been over 1,200 All Terrain drills sold into 23 countries on 6 continents. The Australian market has bought 20 percent of these units.

The All Terrain takes on the US

Wood Construction, Colorado Springs, US installed more than 100,000 ft (30,480 m) of HDPE main line pipe in diameters of 2, 4, and 6 inches using two JT3020 AT machines and one JT4020 AT.

President Ed Libby said “Tests indicated more than half the rock had a hardness of 20,000 psi, and we encountered some that was 31,000 psi. Using larger equipment with mud motors on this project was economically unfeasible – the cost of drilling fluid alone would have been ten times more.

“I’d say if an AT HDD machine can drill in Branson, Missouri, it can drill anywhere.”

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