Through the HDD Technology is possible to lay polyethylene, steel and ductile iron pipes along a drilled profile. The pipes diameter varies from 40 mm up to 1600 mm.
These pipes can be used for a lot of underground services like water transport, oil & gas transport, telecommunication cables and so on.
The drilling profile is designed by a dedicated project and during the work can be followed thanks to a guided system, often a magnetic guided system, in order to avoid natural and artificial obstacles and get the designed goal, working from the Rig side (Rig is called the machine that performs the drilling operations) that is close to the entry point.
The working phase are the followings:
· First of all a pilot drilling has to be carried out through the introduction into the entry point of drill rods with in front a drilling head. When the pilot gets the designed exit point this phase is completed;
· Then a reamer, with suitable diameter according to the diameter of pipelines to be laid, is secured to the pack of pull rods and is pulled back from the exit to the entry point enlarging the pilot hole;
· The last phase regards the pulling back of the pipeline string, made of the welded pipes.
The drilling operations are usually carried out using some drilling fluid, which composition depends on the kind of terrain to be crossed; this fluid (mud) generally consists on water and bentonite (or polymers).
No open trenches along the HDD profile are necessary and when the HDD is completed all the working areas are restored.
For the small pipes the reaming phase can be avoided, moreover both the rigs and working areas can be reduced and the time of work too.
The HDDs are very suitable to overcome obstacles, like rivers, canals, main roads, public areas, archaeological areas and so on and can be used for the consolidation of landslide slopes and the clearance of polluted areas as well.
The soils made of loose gravel and cobbles can be a problem to drill, therefore some preliminary investigations of the terrain to be crossed is necessary.
The soil investigations have to define the accurate stratigraphy along the designed HDD profile and the other preliminary investigations, especially in the urban areas, have to show the presence of other underground services.