Page 240 - Trenchless Technology Piping Installation and Inspection

204 Cha pte r F i v e

Surface drill rig
(applies thrust & rotation,
& drilling fluid) Walk-over
receiver
Fluid allows
supply tracking
2" × 10' 3"
drill head
(semi-rigid)
drill rod Oriented slanted drill
face allows steering
(continuously rotate to
1 drill rod length straight in ground go straight)
(e.g., 10')
Fluid
assisted
Transmitter
FIGURE 5.12 Mini-HDD pilot borehole installations. (Source: Outside Plant
Consulting Services.)

Surface drill rig
(applies pullback & rotation,
& drilling fluid)
Fluid
supply

Reamer
Swivel

Fluid Product pipe
(utility line)
assisted

FIGURE 5.13 Mini-HDD, backream, and pullback operations. (Source: Outside
Plant Consulting Services.)

As mentioned earlier, the drilling fluid helps stabilize the borehole,
remove cuttings, provide lubricant for the drill string and product
pipe, and cool the drill head. The slurry surrounds the product pipe,
typically filling the annulus between the pipe and the bored cavity
and providing a permanent supportive filling. In contrast, for Midi-
and Maxi-HDD operations, and for hard or rocky soil conditions,
“mud motors” powered by the drilling fluids may be used. The use
of such mud motors would only be applicable for the larger Midi-
HDD machines.
Tracking of the initial pilot bore path is accomplished by a manually
operated overhead (walkover) receiver or a wireline (nonwalkover)