Underground Infrastructure - March 2023 - 24

Directional Drilling
safe pulling tension/stress, are also provided in the document.
Because of its high ductility and fl exibility, and ability to be
fused in continuous lengths, per the well-established ASTM
standards and by experienced contractors, PE, particularly
high-density polyethylene (HDPE), is the most commonly
used pipe product for HDD projects.
Although ASTM F1962 is intended for carefully designed,
well-controlled maxi-HDD installations, the methodology
has been extended, via appropriate assumptions and mathematical
simplifi cations, to provide a simpler methodology
that may be advantageously applied to typical, less-controlled
mini-HDD projects.
Th is is the basis of MAB-7 (2020), MAB Guidelines for Use
of Mini-Horizontal Directional Drilling for Placement of HDPE
(PE4710) Pipe in Municipal Applications, as referenced in the
2022 edition of ASTM F1962.
FIGURE 2 illustrates a typical geometry for a maxi-HDD
operation, in this case corresponding to a river crossing. Th e
indicated bore/pipe path comprises three segments spanning
the pipe entry (point A) to its exit point (point D), with horizontal
projected distance Lbore, equal to the sum of the three
horizontal (projected) segments L2
An additional length L1
, L3 and L4
.
exterior to the drilled path allows
for handling at both ends and possible other eff ects (path curvature,
thermal contraction, stretching, etc.). Th e intermediate
horizontal segment, L3
, may be of zero length. " Pipe entry "
point is at the opposite end of the drill rig location, which coincides
with the " pipe exit. "
Th us, FIGURE 2 shows the drilling operation proceeding
from right to leſt , in contrast to FIGURE 1, where the drilling
proceeds from leſt to right.
ASTM F1962 contains 10 main chapters or sections, as
briefl y described below, supplemented by several appendices.
Scope, referenced documents and terminology
ASTM F1962 addresses the overall planning and design, product
selection and installation practices for the placement of
PE pipe using maxi-HDD equipment. Th e primary focus is on
commonly used high-density polyethylene (HDPE) pipe with
a material designation code of PE4710.
For the larger diameters typically used for such applications,
PE pipe is supplied in discrete segments that are fused
together in the fi eld, with essentially no loss in tensile strength,
facilitating the pulling operation.
Preliminary site investigation (Section 4).
Both ends of the bore path must be investigated to confi rm
their feasibility for successfully completing the installation of
the large, long pipeline. Th e drill rig and auxiliary equipment
located on the pipe exit side are relatively large, and require
water access, storage, and mixing and pumping facilities. Th e
pipe entry side, opposite the drill rig, must accommodate the
long length of assembled (fused) pipe.
In addition, there should be a detailed subsurface investigation,
including test borings and soil analysis, to confi rm the
general suitability for the drilling operation, and to determine
the appropriate equipment and hardware.
Safety and environmental considerations (Section 5)
Safety is a primary concern, during any activity, including
construction utilizing maxi-HDD equipment and procedures.
Potential safety issues fall into two general categories:
* Th ose directly related to the setup and operation of the
maxi-HDD equipment (machine and hydraulic operations,
as well as the drilling fl uid under high pressure)
* Th ose associated with accidentally striking buried electric
power lines or other existing pipelines.
Although not considered to be hazardous materials, the
proper handling and disposal of drilling fl uid is also discussed
to avoid possible environmental issues.
Regulations and damage prevention (Section 6)
Depending on the location and extent of the operation, a
variety of permits or approvals may be required, possibly from
federal, state or local jurisdictions. Th ese may include the need
to fi le environmental, health and safety plans, or permits for
passing beneath waterways, and there may be special requirements
for drilling beneath railroads.
Bore path layout and design (Section 7)
Th e planned bore path, such as illustrated in FIGURE 2,
must be consistent with the steering capability of the maxiHDD
equipment, and the bending capability of the drill rods.
Th e stiff ness of the steel drill rods determines their allowable
curvature, in order to avoid fatigue.
Unnecessarily large curvatures (sharp bends) also contribute
to bending stresses in the HDPE pipe, but generally are not
signifi cant for such a fl exible product. Additional route bends,
beyond those shown in FIGURE 2, as well as possible bends in
the horizontal plane, should be avoided, and will increase the
required pulling forces.
Pipe Design and Selection Considerations (Section 8)
Any pipe installed by HDD is subject to loads of a diff erent
FIGURE 2. Typical Maxi-HDD Route (Obstacle or River Crossing)
(Courtesy of Outside Plant Consulting Services, Inc.)
24 MARCH 2023 | UndergroundInfrastructure.com
type and/or magnitude than are experienced in other construction
methods, including by direct burial in a trench. In
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