Horizontal Directional Drilling
Horizontal directional drilling (HDD) is a trenchless construction method used to install pipelines of various
sizes and materials below the ground surface. Trenchless technologies, such as horizontal directional drilling,
pipe bursting and slip lining allow the entire water supply and drainage system of a city to be replaced without
causing a major traffic jam and incurring the enormous cost of restoring streets and roads.
Polyethylene pipe is the pipe of choice for trenchless installations using directional drilling. It's flexibility,
strength and fused joints as strong as the original pipe itself, make it ideal for HDD applications. Horizontal
directional drilling is often used where open cut installations are not feasible, such as road and river crossings.
Using directional drilling techniques to guide a drill string along a bore path under obstacles such as rivers,
lakes, railway crossings or highways, enables replacement of existing water lines, or installation of new ones,
at a relatively rapid rate.
As the hole is bored, a steel drill string is extended behind a cutting head. Drilling mud is used to cool the
cutter and transmitter electronics, to flush excavated soil from the borehole and to lubricate the borehole. The
cutting head is then removed and a back-reamer attached. The pipe string is attached to the back-reamer through a
swivel device. As the drill string is withdrawn to the drilling rig, the back-reamer enlarges the borehole and the
pipe string is pulled into the hole. As with any pipe pulling technique, the movement of the drill string and the
pipe string should be monitored. The pulling load on the polyethylene pipe must not exceed the allowable tensile
load, or safe pull strength of the pipe.
Along with the recent developments in drilling equipment and operator expertise, there has been, and will
continue to be, a dramatic increase in the installation of water and sewer systems using directional drilling.