Directional Drilling Swivels
There is a method for installing pipe know as Horizontal Directional Drilling (HDD).
The first part of the process is to drill a pilot bore using a boring head or rock bit. This is done by rotating the boring head and pushing it into the ground. Drill rods are screwed onto the back of the boring head to form a long string of rods. It is possible to steer the pilot bore under rivers, around hazards etc. by using a radio transmitter to locate it. (See sonde housings).
When the pilot bore is complete the second phase begins which involves make the pilot bore bigger, this is called back reaming. A reamer is rotated and pulled back through the pilot bore enlarging the hole. A series of reamers may be used to enlarge the bore gradually.
The final phase is to pull in the pipe. The drill rods are attached to the back reamer and the pipe has a towing head fitted. The back reamer is rotated as it is pulled through, however the pipe cannot be rotated. To stop the pipe rotating a drilling swivel is used.