Page 41 - Trenchless Technology Piping Installation and Inspection

16 Cha pte r O n e

crossing a road, highway, or railroad track. This process simultane-
ously jacks a steel casing from a drive pit under the road or railroad,
while removing the spoil through the steel pipe by means of a rotat-
ing flight auger. The auger is a flighted tube having couplings at each
end that transmit torque to the cutting head from the auger-boring
machine located in the bore pit and transfers spoil back to the drive
pit. The casing supports the soil around it as spoil is being removed.
Usually, after completion of casing installation, a product pipe is
installed using spacers and the annular space is filled with a grout.
The conventional HAB equipment provides a water hose for grade
control and has no steering capability for alignment. The line and
grade control for HAB equipment are available but not all contractors
have this capability.
Figure 1.13 illustrates a schematic of HAB operation. ASCE
Manuals and Reports on Engineering Practice No. 106, Horizontal
Auger Boring Projects (ASCE, 2004), provides full details on HAB
methods.
The key components of HAB include
• A cutting head, consisting of a set of cutters mounted on the
front face of the boring machine, to cut earth by the rotation
of the cutters
• An auger with its front end connected to the cutting head and
its tail end connected to the prime mover that drives the sys-
tem, to convey the spoil to outside the borehole
• A nonrotating casing around the rotating auger, which is the
pipe to be installed
• A prime mover that provides the torque to rotate the auger
and the cutters, and provides the thrust to advance the pipe
(casing) along with the cutting head and the auger
• A system to inject lubrication (bentonite slurry) around the
pipe, to reduce friction between the pipe and the surrounding
earth in order to facilitate the advancement of the pipe during
the action of boring
• Control and monitoring equipment, such as water-level (most
common), radio tracking systems, or inertia systems

Horizontal Directional Drilling Method
Horizontal directional drilling (HDD) is a steerable system for the
installation of pipes, conduits, and cables along a desired profile
using a surface-launched drilling rig. This method requires the drill-
ing of a pilot bore which is then enlarged with the use of a reamer
prior to the installation of the product pipe. Depending on the diam-
eter of the product pipe, multiple enlargements may be required. The
excavation is performed by fluid-assisted mechanical action of the