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5.3 Maxi-HDD Considerations
Maxi-, and larger-size Midi-, HDD operations are commonly used for
obstacle crossings, such as a river, lake, roadway, an environmentally
sensitive area, and shore approaches, or a combination of such situa-
tions (see Fig. 5.3). Product pipe selection (material, wall thickness,
grade, coating, and others) is an important part of the HDD design
process.
The American Society of Civil Engineers (ASCE) Manual of
Practice (MOP) No. 108, Pipeline Design for Installation by Horizontal
Directional Drilling, and American Society for Testing and Materials
(ASTM F1962), Standard Guide for Use of Maxi Horizontal Directional
Drilling for Placement of Polyethylene Pipe or Conduit Under Obstacles,
Including River Crossings, provide overall guidelines for a Maxi-
HDD operation, addressing preliminary site investigation, safety
and environmental considerations, regulations and damage pre-
vention, bore path layout and design, implementation, and inspec-
tion and site cleanup (ASCE, 2005; ASTM, 2005).
5.3.1 Site Investigation Requirements
As in any construction project, the first step in an HDD installation
is a thorough investigation of the site at which the work will be
undertaken. As part of this investigation, a route must be selected
with sufficient space for the various HDD equipment and opera-
tions. Figures 5.4a and b illustrate the space requirements for the rig
and product pipe sides of the operation. An appropriate site inves-
tigation will also include both surface and subsurface surveys.
Although each survey may be performed by different specialized
engineering consultants, it is important that the results be integrated
onto a single plan and profile drawing, which will be used by the
contractor to price, plan, and execute the HDD operations. Accurate
measurements for this drawing are important, as it will be used by
the contractor for downhole navigation.
FIGURE 5.3 Maxi-HDD installation to cross beneath obstacles.