Horizontal Directional Drilling Using Trenchless Technology
The drill path may be straight or gradually curved. The direction and position of the drill head is monitored by an electronic tracking device and can be adjusted during the pilot bore to steer around obstacles and existing services.
Installation of the product pipe is generally a two-stage operation. A pilot hole is first drilled along the designated path, the bore is then back-reamed to the required diameter to accommodate the product pipe, in either a single or multistage operation depending on the ground conditions and project requirements. On the final ‘pullback’, the product pipe is attached to the reamer via a swivel connector, and is pulled into the bore as the drill string is withdrawn.
Images courtesy of The Australasian Society for Trenchless Technology, www.astt.com.au/instal.htm