Horizontal Directional Drilling


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.

Horizontal Directional Drilling

Technical Information:

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.

A well planned HDD operation includes preliminary survey of the bore path area to determine existing external lines and the soil condition. The choice of the drilling unit depends upon the bore length, the diameter of the pipe to be installed and the soil quality.  Keeping up a certain bore path and gradient course is the main problem of the pilot bore, when the fluid assisted technique fails because of mechanical soil resistance. To overcome this, high thrust and pulling forces are required, reaching the limits of maximum capacity in many cases. Application of Bentonite might relieve the pilot bore and the pipe traction. But experience has proved that the technical and economical advantages of Soft Boring can hardly take effect in difficult soil conditions with coarse grained components and considerable rock inclusions or building rubble deposits. For these conditions, the TT HDD rigs have a built-in percussive hammer which can be switched on additionally, when the drilling progress becomes unsatisfactory due to problematic grounds. In other words, the drilling unit is equipped with the shattering force of a displacement hammer. It is the combination of fluid assisted drilling with an impact unit which makes propulsion and steerability possible.

The high demands and expectations towards the quality of the drilling job waiting to be done require precise detection and steering. Detection is carried out following the transmitter-receiver principle. One operator follows the course of the bore head all the time. All measured values are taken to protocol, directional corrections are passed on to the machine operator via radiophone. It is also possible to directly store the data found in this way, printing them with the help of a PC or Laptop later on. Directional control works according to the "clock-hand principle" via the slanted surface of the head; the head changes its direction in correspondence with the clockwise direction.
On arrival, the bore head is replaced with an upsizing head (backreamer). One or more intermediate upsizing bore follows, or else the pipe is pulled in at once. Pipes up to (for the time being) OD 600 made of plastic, steel and cast iron can be pulled in, single or bundled. When pulling in plastic pipes (especially for gas and potable water pipes), the permissible pulling forces must not be exceeded.

Advantages of the method:

  • 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, Simple technique, Broad application range. 
  • 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, pulling force measurement and position determination possible

Plant Description:

The Horizontal Directional Drilling Rig – The Grundodrill 20S is the most powerful rig in its range, with a 200kN thrust and pulling power, capable to drilling up to 750mm diameter and pulling pipes up to 600mm diameter, with the capacity to drill up to 200m from the launch pit location to the reception pit location depending on the soil type.
The rig comes fully self contained with its own bentonite plant and ancillary equipment. The rig has a bending radius of 75m, is totally controlled using its own tracking system, and can be used in various locations.

Horizontal Directional Drilling Rig & Mobile Bentonite Plant

Horizontal Directional Drilling Rig & Mobile Bentonite Plant

Coffey’s Experience:

Tuam Regional Water Supply Scheme Extension to Athenry - Directional drilled under the main Galway to Dublin railway line as part of the Tuam Regional Water Supply Scheme at Athenry, Co Galway. Prior to carrying out the 17 meters under rail crossing, which was to accommodate a 250mm water main and a 90mm PE sleeve to accommodate an electrical cable,  Coffey’s had to seek approval for the use of this well proven method through Iranrod Eireann (Irish Rail) (IE).  


University of Cork - Directional drill a 300 dia pipe under a river on the University of Cork Campus. The length of the drill from end to end was 20m. The pipe was used to carry various ducts to supply the University.


Dublin Outer Ring Road - Crossing the Nass Road as part of the Dublin Outer Ring Road. The length of the cross was 30m in length. Twin 300 dia pipes were drilled in the ground to carry cable ducts under the road.


Coffey Group, Athenry, Co. Galway, Ireland Tel: +353 91 844356 Fax: +353 91 844519 Email: info@coffeygroup.com