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directional boring
Directional boring, commonly called horizontal directional drilling or HDD, is a steerable trenchless method of installing underground pipes, conduits and cables 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 have been completed, and diameters up to have been installed in shorter runs.
Pipes can be made of materials such as PVC, polyethylene, polypropylene, Ductile iron, and steel if the pipes 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.
==Equipment==
The equipment used in a horizontal directional drilling depends on the outer diameter of the pipe, length of the run, ground conditions and the surroundings above ground. For the large bores, directional drills equipped with as much as 600 tonnes (or more) of thrust/pullback (Vermeer D1320x900)is used in conjunction with a mud reclaimer, excavator, and multiple pumps and hoses to supply the drilling fluid to the drillstem. Directional drilling stem is made from heat-treated high-carbon steel for strength and ships in diameters of Drill stem sections are manufactured in 3.0 or 4.6 and also 9.1 meter lengths and have male threading on one end, and female on the other. It is common for a directional drill to carry as much as of rod on board. Drilling heads come in multiple designs and depends on the rock or soil being penetrated. The drilling head has multiple water ports to allow removal of material. A talon bit involves the carbide-tipped cutters. These allow for steering and cutting the material. Another head is a mud-motor that is used in rocky landscapes.
Furthermore, supporting equipment is needed to assist directional-drilling or HDD to work smoothly, such as drilling mud recycling system, shale shaker, mud cleaner, centrifugal pump, mud tanks, etc.
抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』
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