Page 239 - Trenchless Technology Piping Installation and Inspection

Pr oject Considerations for Horizontal Dir ectional Drilling 203

• Calculation methods
• Copies of field-generated data

It is noted that the position of the desired drill path, and as-built
pipeline, are only as accurate as the preconstruction survey.

5.4 Mini-HDD Considerations
Although typically a lower-cost, less critical operation than Maxi-
HDD, it is nonetheless critical that proper procedures be used in the
planning, equipment setup and operation for a Mini-HDD installa-
tions. Improper procedures may result in compromised utility lines,
including those being installed as well as existing facilities in the
vicinity, sometimes leading to safety hazards. In other cases, the final
installation parameters (location, depth, etc.) may fail to meet the cri-
teria of the inspector or utility owner. Thus, the availability of appro-
priate practices for Mini-HDD operations is extremely valuable. Such
procedures would presumably be performed by contractors and their
personnel that have the requisite skill and formal training, as well as
extensive on-the-job experience.
It is also important, however, that the owners of the facility have a
good understanding of the relevant HDD procedures and practices,
and also participate in the planning and preliminary stages. Further-
more, it is important that owner’s inspectors have sufficient knowl-
edge to help ensure that the product pipes are placed correctly. Issues
of concern include the reliability of the installed product, customer
relations and safety, as well as possible environmental issues. It is
noted that Rule 410C of the National Electrical Safety Code (IEEE,
2007) requires that the contractor provide a designated (qualified)
person (e.g., an operator/foreman) to be in charge of the operation and
equipment, including responsibility for its safe operation.
Mini-HDD is primarily used to install pipes and conduits below-
ground for utility distribution lines along road or street right-of-way,
and to place service lines. Although there are many similarities among
the various HDD categories, this section presents a set of procedures
specific for Mini-HDD, and some Midi-HDD, applications, providing
details for bore planning and product pipe loadings.
Similar to Maxi-HDD operations, the Mini-HDD drill string cre-
ates a pilot borehole which is subsequently enlarged to a greater
diameter during a reaming operation, typically simultaneous with
final pullback of the product pipe or utility line. Figures 5.12 and 5.13
illustrate these two stages of the typical Mini-HDD process. The cre-
ation of the pilot borehole and the reaming operations in Mini HDD
are accomplished by fluid-assisted mechanical cutting provided by
rotating the drill string. The procedure typically uses a high pressure,
but low volume drilling fluid flow, to minimize the creation of voids
during the initial boring and subsequent backreaming operations.