Technique

Directional boring is used for installing infrastructure such as telecommunications & power cable conduits, water lines, sewer lines, gas lines, oil lines, product pipelines etc. It is used for crossing waterways, roadways, shore approaches, congested areas, environmentally sensitive areas, and areas where other methods are costlier. It is used instead of other techniques to provide less traffic disruption, lower cost, deeper and/or longer installation, no access pit, shorter completion times, directional capabilities, and environmental safety.

The technique has extensive use in urban areas for developing subsurface utilities as it helps in avoiding extensive open cut trenches. The use however necessitates that the operator must have the complete information about the existing utilities so then he can plan his hole alignment to avoid damaging those utilities. Since uncontrolled drilling can lead to such damages different agencies/government authorities owning the urban 'right-of-way' or the utilities have formed their rules for safe work execution.

Process

The method comprises a three stage process where in first stage is of drilling a pilot hole on the designed path, second stage is of enlarging the hole by passing a larger cutting tool termed as "Reamer", the third stage is of placing the product or casing pipe in the enlarged hole. The directional control capabilities assist the rig operator in making necessary changes in the directions of the drilling head.

Horizontal directional drilling is done with the help of a viscous fluid known as drilling fluid. It is a mixture of water and, usually, bentonite or polymer continuously pumped to the cutting head or drill bit to facilitate the removal of cuttings, stabilize the bore hole, cool the cutting head, and lubricate the passage of the product pipe.

Watch how HDD method works on YouTube:

http://www.youtube.com/watch?v=ExNCzJMz4vQ&feature=related

http://www.youtube.com/watch?v=ufYMgHa0d18&feature=related

Locating and guidance

Location and guidance of the drilling is very important part of the drilling operation as the drilling head is under the ground while drilling and in most cases not visible from the ground surface. An uncontrolled or unguided drilling can lead to substantial destructions. By properly locating and guiding the drill head such destruction can be avoided.

There are two types of locating equipment for locating the bore head: the ‘walk-over’ locating system or a 'wire-line' locating system. In both of the systems a sonde, or transmitter, behind the bore head registers angle, rotation, direction and temperature data. This information is encoded into an electro-magnetic signal and transmitted through the ground to the surface in a walk-over system. At the surface a receiver (usually a hand-held 'locator') is manually positioned over the sonde, the signal decoded and steering directions are relayed to the bore machine operator. In a wireline system, this information is transmitted through the cable fitted within the drill string.