Effect of a heated drilling bit and borehole liquid on thermoelastic stresses in an ice core

Thermal ice coring processes are accompanied by stresses in an ice core; micro-and macro-cracks are formed. Contamination under mechanical and thermal drilling usually penetrates from 5 to 30mm into the ice core. The quality of ice core acquired by thermal drilling depends on thermal stresses. To improve ice core quality, experimental and theoretical studies have been done. A prototype model of an antifreeze thermal electric drill (ATED) was tested. Temperature distribution in an ice core during thermal drilling was measured with thermocouples. To study temperature and stress distributions in an ice core, a mathematical model was developed. Impacts of ethanol-water solution (EWS) and kerosene on temperature and thermal stresses in an ice core were also studied. The experiments and model simulations have shown that thermal stresses in an ice core are proportional to the ratio of drilling bit length to penetration rate. The maximal thermal stresses in an ice core during thermal drilling exhibit only weak dependence on the type of borehole liquid. Forced circulation of the borehole liquid at the kerf leads to reduced depth of cracks by about 10mm.