Horizontal Directional Drilling

Horizontal Directional Drilling (HDD) is an underground civil construction method used to install a product/utility below the ground’s surface without disturbing the surface or above ground activities. Part of the Trenchless Technology sector, HDD allows a conduit, pipe or cable to be installed below the ground’s surface where other techniques such as open trenching may become difficult, dangerous, time consuming and more costly.

HDD uses a steerable drilling system to allow a pilot hole to be drilled along the required alignment, then resizes via a series of backreamers for the installation of pipes, conduits and cables or other services. Typically this type of drilling is done in a shallow arc using a surface-launched drilling rig but can also be pit launched. The construction of these pits for a HDD operation can be relatively small compared with those required by other Trenchless methods.

The process is generally conducted in four main stages:

• Design of the bore path
• Drilling of a pilot bore which involves the location and steering of a drill bit along the pre-determined bore path from the entry pit to the exit pit
• Staged reaming to open the borehole to the required size
• Installing the product pipe by pulling through the pre reamed borehole