What is Horizontal Directional Drilling (HDD)?

HDD is a method often used on construction projects to install pipelines deep under features like rivers or roads. It involves a drill being sent underground from a rig located on a construction compound. A drill head guides the drill to ensure it follows the planned angle, depth, and exit point. In this case, the drill would go between 20 and 60 metres into the ground. Figure 1 shows what a typical HDD looks like.

During drilling, a mixture of water and bentonite (a type of non-toxic naturally occurring clay which will disperse quickly) is circulated to keep the drilled space open, which prevents collapse, and removes soil and rock debris.

Once the drilled bore is sufficiently open, a pipeline can be pulled through and connected to the rest of the system. However, as this is a trial, we would not install a pipeline but would use this test drill to investigate and analyse ground conditions.