In the event traditional cable percussion or window sampling cannot be used rotary coring is a technique often adopted to form a deep observation borehole or to collect a sample of rock. This drilling method includes a powered rotary cutting head which is on the end of a shaft which will then be driven into the ground as it rotates. In order to keep the cutting head cool this type of system relies on lubrication such as air, water or drilling mud.
Open-hole or core drilling are the two types of rotary boring available. Open-hole drilling means any material recovered will be mixed with the drilling lubricant which makes it unsuitable for effective sampling and is usually too difficult to observe and record the strata. This method would be most suitable for rapid drilling to aid core recovery at a greater depth or for the installation of monitoring wells. Core drilling is done using wire-line, double or triple-tube core barrels that utilise diamond or tungsten-tipped core bits.