Directional Boring (HDD)

Definition - What does Directional Boring (HDD) mean?

Direction boring is a trenchless method of installing pipe, conduit, or cable. Developed in the oil and gas industry, directional boring is a favored option for crossing under rivers, roads and existing structures while minimizing above-ground disruption. Directional boring is what makes trenchless construction possible. The technologies used are now well developed, and the practice has become common in the past several years.


Directional boring is also known as horizontal directional drilling (HDD), horizontal drilling, slant drilling, or deviated drilling.

Trenchlesspedia explains Directional Boring (HDD)

Digging up streets, yards, and other property to lay pipe has traditionally caused major disruptions across cities and neighborhoods. The advent of directional boring has changed that. Using the latest technology, construction workers are now able to install pipes by drilling horizontally, eliminating the need for open trenches. The reduced footprint may include insertion and reception pits while leaving above-ground structures untouched.


The process for directional boring is fairly straightforward. A pilot borehole is created using a steerable drill head. Drilling fluid – usually a combination of bentonite clay – is used to lubricate and cool the equipment as well as remove cuttings. After the initial pass, a reamer is attached and pulled back through the bore hole. Reaming may need to be repeated with larger drill heads until the hole reaches optimal size. Finally, the pipe is attached and pulled through the hole until installation is complete. A location and guidance system is employed throughout the process.


Directional boring has many uses and benefits. It can be used for water lines, sewer lines, gas or oil lines, and other utility conduits. It reduces soil disturbance, protects the ecosystem, limits traffic disruption, and is ideal for sensitive sites. Directional boring can be used under streams or rivers, runways, or golf courses. It can extend for hundreds of yards and may significantly reduce completion time.

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