Experimental study of the drilling process in debris-rich ice

Debris-rich ice is often encountered when drilling into basal ice and rock glaciers. The standard steel bits used for ice core drilling are not suitable because the cutters are very easily broken by rock particles as their hardness and abrasiveness are higher than that of the ice. The tool steel and tungsten carbide inserts are easily damaged in intermixed ice–rock formations. To obtain high-quality core samples in debris-rich ice, it is necessary to find drill bits that can drill ice–rock mixtures with minimal load and acceptable penetration rate and torque. A special testing stand has been designed and constructed to study both standard and custom-made carbide and polycrystalline diamond compact (PDC) drill bits. The results show that both the carbide and the PDC drill bits can drill with high penetration rates in debris-rich ice containing very hard and abrasive granite particles at low drill loads of 500–1200 N. When the rock volume content is 30%, the penetration rates are 4.68 m/h, 5.9 m/h and 11.12 m/h for the standard six-tooth carbide drill bit, a PDC bit with a round compact and a PDC bit with a semi-round compact, respectively, under a drill load of 500 N with a rotation speed of 100 rpm. Within the range of drill loads of 500 to 1200 N and rotation speeds of 50 to 200 rpm, the maximum torque is no more than 45 Nm, and the power consumption is less than 0.8 kW. In addition, the temperature changes of the bit cutters caused by their cutting action were also measured. Results of the preliminary tests show that temperature variations increase from 3.67 to 5.96 °C when the drill load increases from 450 to 1200 N and from 4.17 to 6.21 °C when the rotation speed increases from 50 to 200 rpm.