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Drilling Method
Horizontal Directional Drilling is a surface launch technique, the machine drilling from a small entry
pit at one end of the shot and pulling the pipe back through the ground from the reception pit at the other.
A pilot bore is drilled between the two end points. The drill head contains a transmitting device by means
of which the drill head can be monitored from the surface. Adjustment to the line and level can be made
throughout the process achieving accuracy to within 100mm.
When the pilot bore is complete, the drill head is removed and replaced with an appropriate reamer. This is
pulled back increasing the diameter of the bore. For small pipe a single ream might be sufficient, for
larger pipe stage reaming is necessary, the size of the bore being increased incrementally, reaming as many
times as required using reamers of increasing diameter.
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Drilling fluids, muds, are used throughout the drilling and reaming process. Muds libricate and cool the
drill head, flush away the cuttings and stabilise the bore.
When the bore is of sufficient size the pipe is attached by means of a swivel and towing head and is pulled
in through the bore as the drill string is retracted.
There are specialist techniques, which together with specialist tooling and muds, are capable of installing
pipe whatever the ground conditions.
Horizontal Directional Drilling can be used to install pipe or duct under any structure or around any obstacle.
Installation under roads and motorways, rivers and canals, railways and airport runways are routine.
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