Page 219 - Trenchless Technology Piping Installation and Inspection

CHAPTER 5

Project

Considerations

for Horizontal

Directional

Drilling

5.1 Introduction
Horizontal directional drilling (HDD), one of the most common
trenchless installation methods, allows installation of pipelines and
conduits below ground using a surface-mounted drill rig. The rig
places a drill string at a shallow angle with the horizontal and has
tracking and steering capabilities. Due to the importance and popu-
larity of HDD in trenchless technology industry, a dedicated chapter
is allocated in this book.
For all categories of HDD, of Maxi, Midi, and Mini (see Chap. 1),
a successful installation requires the use of similar practices, including
proper advance planning, equipment selection, and setup. Figure 5.1
illustrates an HDD installation.
Mini-HDD is used for boring holes several hundred feet in length,
for placing pipes of up to 12 in. in diameter and at depths of up to 30 ft.
Mini-HDD is appropriate for placing local distribution lines (includ-
ing service lines or laterals) beneath streets, private property, and
along right-of-ways. In comparison, Maxi-HDD is a relatively sophis-
ticated class of HDD. It is employed for boring holes several thou-
sand feet in length and placing pipes up to 60 in. diameter, at depths
up to 200 ft. Maxi-HDD is appropriate for placing pipes under large
rivers or other broad crossings and obstacles. Applications that are

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