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Pr oject Considerations for Horizontal Dir ectional Drilling 227

successful projects. Improper procedures may result in damaged or
compromised facilities, including those being installed as well as
existing utilities in the vicinity.
Various manuals or guides, as well as software tools, are available
in the industry, to help plan the bore and determine loads applied to
pipelines during a Maxi-HDD installation, including during the sub-
sequent operational stage. In particular, ASTM F1962, provides a
planning and design methodology appropriate for polyethylene pipe.
This chapter provided analogous information for Mini-HDD installa-
tions, including a simplified method for estimating corresponding
loads and evaluating the potential for polyethylene pipe to withstand
the installation and postinstallation forces. Additional details for
such installations are provided in TR-46, Guidelines for Use of Mini-
Horizontal Directional Drilling for Placement of High-Density Polyethylene
Pipe, published by Plastics Pipe Institute (PPI, 2009).
Although the Mini-HDD formulae and methodology discussed
in this book are only applicable to polyethylene pipe, with its charac-
teristically low stiffness, same concept can be used for pipes with
greater stiffness, such as PVC, and possibly steel or iron. It is empha-
sized that it is not the intention to apply the present simplified Mini-
HDD methodology to a large scale, well-engineered Maxi-HDD
operation. For such applications, the detailed design process, and
presumably greater accuracy, associated with more conventional
engineering procedures and trained construction crew, including
application of ASTM F1962 is warranted. The more detailed proce-
dures may more properly account for actual field parameters, such as
bore path entry and exit angles, depth, frictional characteristics, and
buoyancy effects (including possible anti-buoyancy techniques), as
well as more detailed consideration of collapse potential.