IT Technology: Horizontal Directional Drilling ( HDD )

The horizontal directional drilling technique (HDD) is on the way up at the moment. Directional drilling operations unheard of in the past, now belong to the everyday scene on a job site. Application of HDD units make longitudinal installations up to 500 m possible. Crossings beneath rivers and other waters are frequently performed. The directional method even makes drillings beneath industry complexes possible. The range of application includes all pipe construction measures within the bounds of gas, district heating and drinking water supply, the installation of pressure lines for sewers as well as cable protection pipes for television or telephone cables, traffic routing systems, emergency call boxes or low, medium, high voltage and optical fibre cables.

The installation technique is extremely protective towards the environment, causing no ecological damage at all. Minimal damage to the area is only caused within the vicinity of the unit. Several reasons also speak for the application of the directional technique in central town areas. These mainly concern the construction costs, construction periods, permission procedures, soil movement, surface restoration and the traffic, compared to open trenching methods. The normal course taken by the drilling operation is described in the following:
1.  Planning, preliminary survey
2.  Selecting the drilling units and drilling tools
3.  Pilot bore and detection
4.  Reaming(s) or upsizing bore(s)
5.  Pulling in the pipe

Basically, the drilling unit consists of three main system components:
1.  Drill rig / drilling tools
2.  Bentonite mixing system with a two-chamber system and in some cases a recycling system
3.  Hydraulic power unit for driving the Bentonite mixing unit

Advantages of this method are as follows:

• surfaces worth conserving are neither broken up nor damaged, road surface, front gardens etc.), restoration and repair are not required, which leads to high economical advantages
• low social costs, because detours, setting up of signal systems, road blockings, are avoided
• approved technology
• short equipping times - short drilling and construction times
• very economic for river crossings
• supported by the dynamic impact of the percussive hammer 
• thrust and steerability are improved in soil qualities up to class 5, sometimes even class 6
• simple technique
• pulling force measurement and position determination possible 
• broad application range

Reference:
The Horizontal Directional Drilling method with percussive impact
http://pipelaying.tracto-technik.com/Horizontal-Directional-Drilling