Study of Ice Borehole Closure by Finite Element Method

The ice borehole closure may affect the ice drilling operation when the closure rate reaches some critical level. It is essential to estimate the closure rate of ice boreholes for ice drilling program planning. To estimate ice borehole closure under complex ice and boundary conditions, a finite element model was developed. The ice, in this study, was treated as a non-linear, visco-incompressible fluid. Glen's ice flow power law was employed. A direct iteration method was used.

Verification studies using Nye's formula show that the model gives accurate results in closure rate, strain rate and stresses with errors at the 4th digit in strain rate. Test with field measurements show that the exponent of power law should be considered as variable of ice effective stresses to get more accurate results. An empirical relation between the exponent and effective stress was obtained with field measurements. Nye's formula is effective under ordinary ice conditions.