Boreholes in overburden drilling are used if there are no requirements for a stable borehole or sealing against aquifers (e.g. groundwater).
With overburden drilling boreholes, the casing (outer pipe) and drill pipes (inner pipe) are driven either in a ‘rotating – rotating’ or ‘rotating – hammering’ manner, depending on the system in use. The flushing medium is pressed through the drill pipes (inner pipe) and is forced back out again at the mouth of the borehole or at the discharge head, along with the loosened drill cuttings, through the annular gap between the drill pipes (inner pipe) and the casing (outer pipe).
In many cases, overburden drilling is performed using a down-the-hole hammer. The hammer is directly connected to the drill pipes and is driven by the flushing medium (e.g. compressed air).
There are several different ways to drive the casing and the drill pipes in the manufacture of overburden drilling.
A distinction is always made as to whether the casing and the drill pipes are to be driven synchronously (iRH-oRH / iLH-oLH) or in counter directions (iiRH-oLH / iLH-oRH). Depending on the foundation-soil requirements and boundary conditions involved, a very wide variety of auger drives can be used.