Horizontal directional drilling (HDD) is an internationally-accepted underground construction technology — the most versatile of any trenchless procedure for placing utility pipe and cable in the ground.

Agio Ehitus, based in Tallinn, the capital and largest city in Estonia on the banks of the Gulf of Finland, has specialized in directional drilling for 11 years, serving a variety of clients in Estonia, Latvia and Lithuania.
Projects include installations for telecommunications networks, electrical cables, and water and sewer systems, said Alexander Nikonovich, Agio Ehitus. In most instances, Agio Ehitus works as a subcontractor for the HDD portions of projects.

Directional drilling is described by Agio as the “close” method of construction as opposed to the “open” (excavation) method of construction.

Project owners in Estonia and surrounding countries are well aware of the benefits of the method, said Nikonovich.

“The close method is low cost and provides a short time for work completion,” he said. “It provides reduction of soil transportation and utilization expenses, as well as that of labor input and prevents hold-ups in traffic. One can also avoid damage of available communications that can occur when digging the soil.”

The technology is well suited for projects in city areas where it is important not to damage surface improvements and interrupt normal activities. It also is used in open areas for crossing rivers and other bodies of water and in environmentally-sensitive areas where other types of construction cannot be used.
Currently, Agio operates two Ditch Witch JT3020 All Terrain (AT) directional drilling machines, which employ a dual-pipe, mechanical drilling drive systems which enable the relative small machines to work effectively through rocky formations.

Two recent projects illustrate the versatility of HDD’s close method of construction.

A project in Tallinn to installed 110 kV power cable required 15 bores to install a bundle of PE casings: three 8-in. in diameter for electrical cable, and one 1.5-in. in diameter for fiber-optic cable. The average bore length was 492 ft with the shortest being 262 ft and the longest 656 ft. The route of the bores was under the footway adjacent to Peterburi Road in the city, which permitted placing the ducts without interrupting traffic.
Subsurface soil conditions were limestone. Depths varied to 13 ft at the deepest. The AT system effectively bored through the limestone using a tri-cone TCI bit. The pilot hole was first enlarged with a 12-in. Rockmaster backream, then a 23-in. backreamer, followed by pulling in the PE pipes behind a 20-in. Kodiak reamer.

The 15 installations were completed over a period of five months.

A project in Ogre, Latvia, required one 656-ft long bore to install 12.4-in. diameter PE pipe for drinking water beneath a river. Subsurface conditions were rocky soil. At the deepest point, the pilot hole reached 39 ft. A 5.5-in. tri-cone bit was used. The pilot hole was enlarged with a 16-in. backreamer.

The Ditch Witch JT3020 AT is a compact, self-contained HDD unit that develops 30,000 lbs of pullback, 4,000 ft-lbs of spindle torque, and maximum spindle speed of 225 rpm. Mounted on rubber tracks, the equipment easily moves across paved surfaces and landscaped areas with minimal disturbance, as well as across open country.

The AT dual-pipe, mechanical drilling system uses an inner pipe to drive a rock bit and an outer pipe to provide rotary torque and to steer the downhole tool when drilling the pilot bore. The AT system delivers maximum downhole horsepower and operates on low volumes of drilling fluid and enables relatively compact equipment to drill through rock without a mud motor, something other equipment in its class are unable to do. All Terrain models also are productive in almost all types of non-rocky soils.

In addition to HDD construction, Agio Ehitus replaces failing segments of sewer pipelines using the pipebursting process by which a tool is pulled through a section of old pipe, cracking and bursting the pipe as it proceeds while simultaneously pulling in a section of new pipe.

Agio Ehitus is licensed for construction and repairs on water supply and sanitary sewer systems, external heating systems, general construction work, and construction supervision. Ditch Witch of the Baltics, Vilnius, Lithuania is the dealer for Agio Ehitus.

Jeri Lamerton is public relations manager for Ditch Witch.

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