Horizontal Directional Drilling (HDD) is a construction method used to install a product/utility below the grounds surface on a horizontal plan without disturbing the surface or above ground activities. Part of the Trenchless Technology group and methods, HDD allows a conduit, pipeline, cable etc to be installed where other techniques such as open trenching would become dangerous, messy, time consuming and at times impossible to construct.

The HDD procedure consist of three major objectives:

  1. The Pilot Bore
  2. Reaming Process
  3. Product Installation

2.  Reaming Process

Once the pilot hole is complete, the drillhead is removed and a back reamer attached to the drill string. The reamer is then slowly pulled back through the hole whilst being rotated. As the reamer enlarges the hole, the cutting again mix with the drilling fluid being pumped through the drill rods to help stabilise the hole and ensure flow continues to the exit pit. Several different size reamers maybe required to bring the hole to its designated size.

  

3.  Product Installation

Once the bore hole has been enlarged to its correct size and the hole is cleaned out, the product is connected to the reamer via a pipe puller, several metres of chain and swivel. As the product is being pulled back through the bore hole, drill slurry is forced into any voids that may a have been produced around the product. This is where the correct drilling additives used are so important. Once the product has entered the entry pit is it disconnected from the drill string, HDD machine is removed, site returned to its original condition and all open pits made safe including fencing.

  

  
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TRENCHLESS ADVISOR PTY LTD

1. The Pilot Bore

Through the use of a drillhead, which penetrates into the ground formation, a bore hole is produced below the surface in line with the designated bore path. The drillhead location is monitored at all times by the use of a transmitter located in the drillhead sending information to a receiver on the surface. This information tells the operator the drillheads lateral position, depth & pitch as well as drillhead temperature The bore path may require the drillhead to steered around existing services or below a structure such as a road, buildings, railway or even waterway. During the entire process, drilling fluid is pumped through the drill rods and out through the drillhead. This specialised drilling fluid mixers with the cuttings to form a drill slurry which helps stabilise the hole, suspend cutting & prevent frac-outs. Once the drillhead enters the exit pit, which has been constructed at the other end of the bore path, the pilot bore has been completed.