Page 249 - Trenchless Technology Piping Installation and Inspection

Pr oject Considerations for Horizontal Dir ectional Drilling 213

140
Rise distance (100 ft. radius of curvature)
120
Total horizontal rise distance, S 5 , ft 100 20° (36% grade)
5° (9% grade)
10° (18% grade)

80
13° (58% grade)
60
40

20

0 Rise at constant curvature, S 3
0 50 100 150 200 250 300
Depth, in.
FIGURE 5.18 Horizontal rise distances. (Source: Outside Plant Consulting
Services.)

For a drill head oriented at an upward grade, the horizontal dis-
tance to rise to the surface (e.g., from point 4) is

S = d /Tan α
4 4
≈ d /α (5.10)
4
where S = distance to rise to surface at constant rise angle, ft
4
d = depth, ft
4
The values for the depth d and elevation angle α used in the
4
above formula may be obtained by information provided by the drill
head locating system. This formula corresponds to a rise at a constant
grade angle, and the results are shown in Fig. 5.19.

5.4.3 Overall Bore Path Layout and Design

Bore Path (Horizontal) Planar Trajectory
In plan view, typical bore paths are relatively straight trajectories
between the entry and exit points, and pass through intermediate
access points, as required. A degree of route curvature in the hori-
zontal plane may be accommodated by the steering capability of the
Mini-HDD system, consistent with the recommended bend radius
of the drill rods (and product pipe) and steering capability within
the soil.