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Horizontal Directional Drilling Improving Baltic Region Infrastructure


Horizontal directional drilling (HDD) is an internationally accepted underground construction technology, considered to be the most versatile trenchless procedure for placing utility pipe and cable in the ground.

Agio Ehitus, a contractor 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 cable and water and sewer systems. In most instances, Agio Ehitus works as a subcontractor for the HDD portions of projects.
Directional drilling is considered the “closed” method of construction, as opposed to the “open” excavation method. Project owners in Estonia and surrounding countries are well aware of the benefits of directional drilling, says Alexander Nikonovich of Agio Ehitus.

“The closed method is low-cost and provides a short time for work completion,” says Nikonovich. “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.”

HDD 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. The JT3020 All Terrain features a dual-pipe, mechanical drilling drive system that enables this relatively small machine to work effectively in rocky conditions.

Two recent projects illustrate the versatility of the horizontal directional drilling method.

A project in Tallinn to install 110-kV power cable required 15 bores to install a bundle of PE casings: three
8-in. diameter casings for electrical cable, and one 1.5-in. diameter casing 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 Tallinn’s Peterburi Road, which permitted placing the ducts without interrupting traffic. Subsurface soil conditions were limestone. Depths varied, with the deepest being 13 ft. 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 backreamer, then a 23-in. backreamer, followed by pulling in the PE pipes behind a 20-in. Kodiak backreamer.

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 beneath a river. The pipe would serve as a conduit for drinking water. Subsurface conditions were rocky soil. At the deepest point, the pilot hole reached 39 ft. A 5.5-in. tri-cone bit was used, and the pilot hole was enlarged with a 16-in. backreamer.

A Ditch Witch JT3020 All Terrain is a compact, self-contained HDD unit that develops 30,000 lbs of pullback, 4,000 ft-lbs of spindle torque, and a maximum spindle speed of 225 rpm. Mounted on rubber tracks, the equipment easily moves across paved surfaces and landscaped areas with minimal disturbance, and also travels efficiently 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 steer the downhole tool when drilling the pilot bore. The AT system delivers maximum downhole horsepower and operates on low volumes of drilling fluid, enabling this relatively compact machine to drill through rock without a mud motor—something other equipment in the same horsepower class is unable to do. All Terrain models also are productive in almost every type of non-rocky soil.
In addition to HDD construction, Agio Ehitus replaces failing segments of sewer pipelines via pipebursting, a method by which a tool is pulled through a section of old pipe, cracking and bursting the pipe while simultaneously pulling in a section of new pipe.

Agio Ehitus is licensed for construction and repairs on water supply, sanitary sewer, and external heating systems, and also for general construction work and construction supervision.
This article was supplied by Ditch Witch, headquartered in Perry, Okla.

Courtesy trenchless technology

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