page_title: Directional boring
section_title: Locating and guidance
hierarchical_section_title: Directional boring / Locating and guidance
caption_attribution_description: Pipes layed by a horizontal drilling machine
context_page_description: Directional boring, also referred to as horizontal directional drilling, is a minimal impact trenchless method of installing underground utilities such as pipe, conduit, or cables in a relatively shallow arc or radius along a prescribed underground path using a surface-launched drilling rig. Directional Boring/HDD offers significant environmental advantages over traditional cut and cover pipeline/utility installations. The technique is routinely used when conventional trenching or excavating is not practical or when minimal surface disturbance is required.
  Although often used interchangeably, the terms directional boring and horizontal directional drilling are distinct in that they convey a different sense of scale. The term "Directional Boring" or "Bore" is generally reserved for mini/small sized drilling rigs, small diameter bores, and crossing lengths in terms of hundreds of feet. Generally, the term Horizontal Directional Drilling is intended to describe large/maxi sized drilling rigs, large diameter bores, and crossing lengths in terms of thousands of feet.
context_section_description: Location and guidance of the drilling head is an important part of the drilling operation, as the drilling head is under the ground while drilling and, in most cases, not visible from the ground surface. Uncontrolled or unguided drilling can lead to substantial destruction, which can be eliminated by properly locating and guiding the drill head.
  There are three types of locating equipment for locating the bore head: the walk-over locating system, the wire-line locating system and the gyro guided drilling, where a full inertial navigation system is located close to the drill head.
  Walk-over locating system — A sonde, or transmitter, behind the bore head registers angle, rotation, direction, and temperature data. This information is encoded into an electromagnetic signal and transmitted through the ground to the surface in a walk-over system. At the surface a receiver (usually a hand-held locator) is manually positioned over the sonde, the signal is decoded and steering directions are relayed to the bore machine operator.
  Wire-line locating system — The wire-line system is a magnetic guidance system. With a magnetic guidance system (MGS), the tool reads inclination and azimuth. The MGS, also has a secondary means of location verification utilizing wire grids laid on the ground surface. It is the only system that has the capability of verifying the location. This information is transmitted through the wire-line fitted within the drill string. At the surface, the navigator in the drill cab performs the necessary calculations to confirm the parameters have been met. The MGS, even without the use of the wire grid, has been accurate to over 2 km with an accuracy of 2% at depth. The operator of the MGS communicates with the driller and guides him towards a predetermined engineered drill path.
  Gyro-based locating system — The gyro based system is fully autonomous and therefore one of the most accurate systems where sufficient diameter (200 mm) is available and where long distances (up to 2 km) have to be traversed with minimal deviation (less than 1 m position error). Currently the actual depth is not verifiable without the use of surface coils, a near surface transponder or sonde used in walkover systems.
  All three systems have their own merits, and a particular system is chosen depending upon the site requirements.
caption: Empty conduits laid by directional boring
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