In the case of rotary percussive drilling with top hammer, the drill pipes are driven into the soil and turned at the same time. The flushing medium is pressed through the insides of the drill pipes and is forced out again at the mouth of the borehole, along with the loosened drill cuttings, through the annular gap between the drill pipes and the borehole wall.
Particularly where self-drilling anchors are in service, devices known as ‘hydraulic hammer drills’ are used to drive the pipes. These top hammers are directly connected to the drill pipes and drive them ‘from the outside’. The rotation of the drill pipes is conveyed through a transmission that usually connects the hydraulic hammer directly to the drill pipes.
Under the self-drilling anchor process, the drill pipes, together with the drill bit, also form the future anchor; this is why they remain in the soil. Here, the drill pipes are a hollow threaded rod through which a cement suspension is forced as a flushing medium through the drill bit and into the annular gap between the drill pipes and the borehole wall. After curing, the cement suspension forms the static linkage between the ground and the self-drilling anchor.
Alternatively, in the case of rotary percussive drilling with top hammer, there are also drill pipes in the form of thick-walled casing pipes with threaded ends that are used with full-face, core or lost drill bits, depending on the application. Once drilling depth is reached, usually a rod or strand anchor is inserted into the casing pipe and the drill pipes are retrieved. At the same time, the anchor is filled with a cement suspension.
This process can be used to produce both short- and long-term anchors. Typical applications include: