Horizontal directional drilling

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HDD system for pipe pulling
HDD system in use

The horizontal directional drilling method is a directional drilling technique for horizontal drilling ( English " Horizontal Directional Drilling ", HDD). This means that pipes can be laid underground without having to dig a trench . The holes can be several hundred meters long. For the majority of all holes, diameters up to a maximum of 700 mm are sufficient.

The horizontal directional drilling rig drills an underground channel and pulls in one or more product or empty pipes as it retreats. In conduits lines can later eg electricity or telecommunications are drawn or blown. Horizontal directional drilling systems work with pulling and pushing force, torque (rotation), flushing and dynamic impact force. The HDD system consists of a horizontal directional drilling system, bentonite mixing system and a drive station for operating the mixing system.


As a rule , a pit is dug both at the beginning and at the end of the desired route , and also in between for longer stretches. The horizontal directional drilling rig then drills a pilot hole with a drill head in the direction of the target pit. The drill head is screwed to the drill string, which is screwed together from piece-wise drill string, which is driven into the ground by the horizontal directional drilling system and has a certain flexibility.

A smaller diameter of the drill rod compared to the drill head leaves an annular space free. Through the linkage is a bentonite - drilling fluid pumped to the drill bit, where it exits and flushes the cuttings through the annulus. In addition to clearing out the special properties of bentonite, it serves to stabilize the drill channel, to cool the drill head and as a lubricant .

The direction of the drilling can be changed due to the flexibility of the rods and the controllability of the drill head. Initially, the hole is usually directed diagonally downwards into the ground and then runs in a slight arc to the target, where it emerges again diagonally upwards.

Backreamer with the pipe to be drawn in

Has reached the target pit the drill head, he is against a so-called clearer (in technical language also english "reamer" exchanged). The reamer has a larger diameter than the drill head and, when withdrawn, expands the pilot bore while at the same time compressing the bore walls. When attached to the reamer, either another drill string or finally one or more pipes can be pulled into the drill channel for further expansion steps.

If the drilling progress is unsatisfactory due to poor subsoil conditions, the dynamic hammer mechanism can be switched on. The drilling rig is supported by the hydraulic impact force of a displacement hammer with up to 1500 blows per minute. This means that propulsion and controllability are even possible in soil classes 5 and 6.

Control of the drill head

Example drill head of an HDD system

The steerable drill head is flattened on the side and contains a transmitter that enables the three-dimensional position as well as the direction, inclination and angle of the drill head to be determined with centimeter precision. With a rotating advance, the drill works straight forward. If the rotation is stopped and the drill is driven in pure pushing operation, or in the case of solid floors in hammering, with the support of the flushing nozzles, it drifts off due to the flattening according to its respective position. With the help of the transmitter, the drill can be brought into the desired position and the drilling direction can be changed and adjusted along the way.


The directional drilling method is common in trenchless pipeline construction. Due to the low cost compared to digging a trench and the associated high route performance (typically over 100 meters per working day), the horizontal flush drilling is the dominant method when laying pipes or cable lines underground.
The method is particularly suitable for

  • Pipe laying in inner cities
  • Passing under
    • flowing waters
    • Track systems
    • Runways of airports
    • Roads, highways
  • laying cables in nature reserves , as earthworks can be minimized.

See also


  • DWA -A 125 - pipe jacking and related processes
  • DWA-A 161 or DVGW-M GW 312 - Static calculation of jacking pipes
  • DVGW -M GW 321 - Controllable horizontal directional drilling methods for gas and water pipelines - Requirements, quality assurance and testing


  • Hans-Joachim Bayer (Hrsg.): HDD practical manual , terms and bandwidth of HDD, HDD machines and accessories, practical reports, HDD market partner, Vulkan, Essen 2005, ISBN 978-3-8027-2734-4 .
  • Sascha Bunger: Fundamentals of horizontal drilling technology , Vulkan, Essen 2007, ISBN 978-3-8027-5325-1 .
  • Let Elbe; Dirk von Ameln (Ed.): Drilling fluids in the HDD , Vulkan, Essen 2003, ISBN 978-3-8027-5386-2
  • Hermann Schad, Tobias Bräutigam, Steffen Bramm: Pipe jacking : Pressing accessible lines. 2nd edition, Ernst, Berlin 2008, ISBN 978-3-433-02912-1
  • Dietrich Stein: Trenchless line construction . Ernst & Sohn , Berlin 2003, ISBN 3-433-01778-6 ( limited preview in the Google book search).

Web links