How does HDD work?

1 September 2020

Horizontal directional drilling or HDD is generally accomplished in 3 principle phases: pilot bore, reaming process and pipe installation. A small diameter pilot hole is drilled along a prescribed underground path from the surface entry and exits points. This pilot bore is then enlarged through a reaming process to a diameter that will facilitate pipe installation. The pipeline is pulled into the enlarged hole, thus creating a continuous underground pipeline exposed only at the surface entry and exit points. HDD facilitates the need for pipelines crossing under roadways, runways, railways, wetlands and rivers no matter the size or depth needed.

DirectHitt Trenchless HDD process

1.  Pilot Bore

A pilot bore is the initial hole drilled during HDD that spans the entire length of the hole. The pilot bore is usually performed with a steerable drill head. The drill head is drilled along the prescribed underground path starting at the surface entry point with depth and alignment continuously monitored through to the surface exit point.

DirectHitt Trenchless Pilot Bore

2.  Reaming Process

The pilot bore is then enlarged by back reaming the hole with cutters designed for the specific underground conditions. The pilot bore is enlarged to a size that accommodates the required pipeline. The finished hole can often be 50 per cent larger than the pipes. The back reamer not only enlarges the hole, but it also provides a structurally sound and smooth bore for the pipe installation.

DirectHitt Trenchless Reaming Process

3.  Pipe Installation

Pipe installation is the process of pulling or even pushing the pipe into place through the bore. This is the final pullback stage where the product pipe is attached to the back reamer via a swivel connector, or the product pipe is connected to a drill string. All HDD machines use a drilling fluid that is designed to lubricate and stabilise the bore, as well as transfer the excavated material in suspension.

DirectHitt Trenchless Reaming Process

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Be sure to contact the Directhitt team by giving us a call or completing our online contact form to enquire about our horizontal directional drilling service. We’ll organise a free personalised quote for your next HDD project across Australia.

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