The purpose of exploratory and reconnaissance boreholes is to extract an complete core of the foundation soil to be examined. This is achieved by means of rotary core drilling. To achieve the best possible result, it is crucial not only to choose the right drill bit and drill pipes. The drill itself must also have the capability for adjusting rated speed and drill contact pressure, along with a flushing device.
In core drilling, a basic distinction can be made between single- and double-core barrels.
If a single-core barrel is used, the flushing medium (water) flows between the casing pipe and the core. The problem that this creates for sensitive samples is that the core will be eroded and damaged.
If double-core barrels are used, the core only comes into contact with the flushing medium at the end of the pipe. This is a much more effective way to protect the core from erosion. If a plastic pipe is additionally fed into the in the inner pipe, this is referred to as ‘a triple-core barrel’. This method is used if rock samples are sensitive to water or susceptible to swelling.