The Horizontal Directional Drilling method with percussive impact

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

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 in difficult soil qualities up to grade 5, sometimes even grade .
 

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.

 
 Click the image for an animation
Animation courtesy of Allen Watson Ltd.

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 (in Germany according to GW 321, 322,323). On the client's demand, the pulling forces applied to the pipe have to be measured and taken to protocol. TRACTO-TECHNIK can supply a simple pulling force measuring device.

The exact position of the pipe installed can be determined after completing the drilling job with Grundocontrol from TRACTO-TECHNIK.

The horizontal directional drilling method is described in the German guideline ATV-A 125 and in the GW 304 Pipe Laying as well as in other German standards.

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
• 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

The family of steerable boring systems has been developed further and re-arranged.
The P family comprises the Grundopit steerable mini boring systems.

With the Grundodrill X family TT meets the growing need for a simple, reliable, and rugged machine class. All important components are arranged in such a way that they are quickly, easily, and conveniently accessible for checks or replacement. Only high-quality components of top manufacturers are used in the construction of Grundodrill X machines to reduce the probability of component failure (and drill downtime) to a minimum. The small machine dimensions enable bores in limited space. The X family comprises the models Grundodrill 4X, Grundodrill 7 Xplus TD, Grundodrill 10 XP and 15 XP.

The N Family with models Grundodrill 15 N and Grundodrill 25 N is can precisely be adapted to the customer's requests. On the same undercarriage a basic model as well as a premium model is available, each with various options. The highest drive performance in this bore rig class allows for maximized technical values, which so far had been unachieved regarding pulling force, torque and rinsing performance.