Directional boring, commonly called horizontal directional drilling or HDD, is a steerable trenchless method of installing underground pipes, conduits and cables in a shallow arc along a prescribed bore path by using a surface launched drilling rig, with minimal impact on the surrounding area. Directional boring is used when trenching or excavating is not practical. Directional boring minimizes environmental disruption. It is suitable for a variety of soil conditions and jobs including road, landscape and river crossings. Installation lengths up to 6,500’ (2,000m) have been completed, and diameters up to 48” (1,200mm) have been installed in shorter runs. Pipes can be made of materials such as PVC, polyethylene, Ductile iron, and steel if the pipes can be pulled through the drilled hole.

Technique

The process is used for installing infrastructure such as telecommunications & power cable conduits, water lines, sewer lines, gas lines, oil lines, product pipelines and environmental remediation casings. It is used for crossing waterways, roadways, shore approaches, congested areas, environmentally sensitive areas, and areas where other methods are costlier.
Directional boring 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.
 
Drilling Process

The method comprises a three stage process wherein 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.
 
Drilling Fluid

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.
 
 
 
 

Locating & 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.
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.