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Directional drills

Directional drills force a drill string through softer types of ground by hydraulic force. A wedge shaped head and water jet cutters ease the way. The wedge tends to be forced sideways and can be steered around, under or over obstacles by turning it as required. Continuous rotation creates a straight line. A radio sonde tells a detector above ground the precise position.

'The hollow string is pulled back with a reamer to widen the bore and a fluid pumped behind to keep the borehole open, ' Kaminik explains. Usually this is bentonite, although polymers are used in porous ground. A second larger ream is made and then a previously welded length of typically plastic pipe is pulled through. A typical run is 90m between small excavated pits.

Kaminik recently visited Germany's Tracto Technik (TT) to see advances in HDD techniques.

TT makes a combined HDD and impact mole where the head 'hammers' through the ground.

Kaminik is also interested in a real time strain system from American Augurs, which displays the load on the pipe as it is pulled through, and other data logging systems such as those available from Digitrak and Radiodetection.

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