ABSTRACT

We describe a portable drilling system that uses compressed air for coring permafrosted glacigenic sediments to depths of 10 meters. Standard HQ and NQ diameter core barrels, bits, and drill rods were used with a purpose-built, portable compressor, which could produce 50 cubic feet (1.4 m³) of air per minute at 30 psi (200 kPa). The drill string was rotated by a Stihl 056 motor mounted on a frame and hung from a hand winch on a tripod. The supply of compressed air is critical to keep the drill bit at subzero temperatures and prevent melting of the core and nearly instantaneous freeze-up of the drill string should rotation unexpectedly stop. Cooling the bit depends on the temperature and volume of air entering the hole as well as the kerf and diameter of the bit. Diamond bits are best for coring igneous clasts, but tungsten bits are best for coring ice lenses and soft friable sands. Good core recovery of unconsolidated sands and gravels is possible only if they are firmly frozen in place.