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31

What is HDD Drilling?

Horizontal Directional Drilling (HDD) is a technique used in situations where pipe, cable or conduit needs to be installed horizontally underground, such as beneath buildings, roads, rivers, or other obstacles. As a market leader and innovator in horizontal directional drills in Perth for over 20 years, our clients can be confident that the Vermeer range of utility HDD rigs has the best possible solution for their project.

HDD is the preferred option where, for practical or design reasons, trenches cannot be dug. It is an efficient and innovative process which utilises specialised horizontal directional drills and equipment to precisely drill along the chosen bore path and back ream the required pipe.

 How is HDD done?

  • Step 1 – The Pilot Hole

The first step is to create a bore plan locating existing utilities, position the entry and exit pits then drill a small diameter pilot hole to the pre-determined bore path. The pilot hole is precisely tracked using a walkover guidance system or, for more complicated jobs, a wireline magnetics type system. A transmitter near the drill head sends a signal to the engineer giving the exact position of the drill. Depth, alignment, and percent slope of the drill head are constantly monitored.

Drilling fluid is an essential component of the process. The fluid is pumped through the drill pipe to the drill bit where high-pressure jets and the bit cut through the soil. The drilling fluid then carries the cuttings back to the entrance pit.

  • Step 2 – Pre-reaming

The next step is to pre-ream the pilot hole and enlarge it to the required size. Pre-reaming ensures that a finished hole has optimal integrity. It is done after drilling the pilot hole but before the pipe, cable or conduit is installed in the pullback stage. A reamer is rotated within the hole while pumping more drilling fluid to both remove solids and enlarge the hole. Depending on the particular project and local soil conditions the pre-reaming process may require multiple passes of increasingly larger reamers. In addition to drilling fluid, additives such as Bentonite will be used to help control fluid loss or infiltration and so ensure a clean and stable hole. Other additives, such as polymers, may also be used to help break up clay soils.

  • Step 3 – Pipe Pullback

The final step and most important part of the HDD process is the pullback of the pipe within the pre-reamed hole. Pullback requires that the drill rod and reamer be attached to a swivel, which is utilized between the prefabricated product pipe to be installed and the reamer. This will prevent any stress from the drill damaging the product pipe. Once again, as the product pipe is pulled into and through the drill hole, drilling fluid is pumped through the hoke to lubricate the product pipe.

 Complete our online enquiry form today to discuss your HDD needs with our experts. For further reading on the HDD process, we recommend  trenchlesspedia.com.

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