Directional boring, commonly called horizontal directional drilling or HDD, is a steerable trenchless method of installing underground pipe, conduit, or cable in a shallow arc along a prescribed bore path by using a surface-launched drilling rig, with minimal impact on the surrounding area. Directional boring is used when trenching or excavating is not practical. It is suitable for a variety of soil conditions and jobs including road, landscape and river crossings. Installation lengths up to 2000 m have been completed, and diameters up to 1200 mm have been installed in shorter runs. Pipe can be made of materials such as PVC, polyethylene, polypropylene, Ductile iron, and steel as long as it can be pulled through the drilled hole. Directional boring is not practical if there are voids in the rock or incomplete layers of rock. The best material is solid rock or sedimentary material. Soils with cobble stone are not recommended. There are different types of heads used in the pilot-hole process, and they depend on the geological material.
Horizontal directional drilling (HDD) was pioneered in the United States in the early 1970s by an innovative road boring contractor who successfully completed a 183 m (600 ft) river crossing using a modified rod pushing tool with no steering capability (DCCA 1994). By integrating existing technology from the oil well drilling industry and modern surveying and steering techniques, today's directional drilling methods have become the preferred approach for installing utility lines, ranging from large-size pipeline river crossings to small-diameter cable conduits.
The HDD industry is divided into three major
sectors--large-diameter HDD (maxi-HDD), medium-diameter HDD (midi-HDD), and small-diameter
HDD (mini-HDD, also called guided boring)--according to their typical
application areas. Although there is no significant difference in the operation
mechanisms among these systems, the different application ranges often require
corresponding modification to the system configuration and capacities, mode of
spoil removal, and directional control methods to achieve optimal
cost-efficiency. Table 1 compares typical maxi-, midi-, and mini-HDD systems.
Table 1. Comparison of main features of
typical maxi-, midi-, and mini-HDD (Iseley and Gokhale 1997)
| System Description | Product Pipe Diameter | Depth Range | Drive Length | Torque | Thrust/ Pullback | Machine Weight (including truck) | Typical Application |
| Maxi-HDD |
600-1,200
mm
(24-48
in)
|
< 61 m (200 ft) |
< 1,818 m
(6,000
ft)
|
< 108.5 kN-m
(80,000
ft-lb)
|
< 445 kN
(100,000
lb)
|
< 267 kN
(30
ton)
|
River, Highway crossings |
| Midi-HDD |
300-600
mm
(12-24
in)
|
< 23 m (75 ft) |
< 274 m
(900
ft)
|
1-9.5
kN-m
(900-7,000
ft-lb)
|
89-445
kN
(20,000-100,000
lb)
|
< 160 kN
(18
ton)
|
Under
rivers and roadways
|
| Mini-HDD |
50-300
mm
(2-12
in)
|
< 4.5 m (15 ft) |
< 182 m
(600
ft)
|
< 1.3 kN-m
(950
ft-lb)
|
< 89 kN
(20,000
lb)
|
< 80 kN
(9
ton)
|
Telecom
and Power cables,
|
Daftar Pustaka :
https://en.wikipedia.org/wiki/Directional_boring
http://rebar.ecn.purdue.edu/Trenchless/secondpage/Content/HDD.htm
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