A pilot hole is horizontally drilled and continues under and across the obstacle (eg a motorway) along a predetermined design path. An electronic transmitter (placed in the drill head) transmits information back to the directional drill rig operator. The directional driller then, by using the relayed information, can accurately control the bore path around or under any obstructions.
Once the pilot hole has been completed, the second step is to enlarge it to a suitable size to install the product pipeline. This is accomplished through “pre-reaming”. The reamer is attached to the drill string and pulled back through the pilot hole.
To help with the stability of the bore hole, additives are used to maintain the integrity of the hole and flush out cuttings.
The final step is the pullback of the pipe within the pre-reamed hole. A reamer is attached to the drill string, and then connected to the product by a pulling head and swivel. The swivel allows for the reamer to turn without the product turning.
As the product pipe is pulled into the drill hole, drilling fluid is pumped downhole to provide lubrication to the product pipe. The pullback continues until the reamer exits the bore path.