Effect of physical properties of frozen ground on electrical resistivity logging

Abstract

During a two-month period from late April to early July 1990, variations of apparent electrical resistivity and temperature with time in the upper 4 m of a silty permafrost were recorded at Umiujaq, Nunavik (Canada). Electrical contact with the ground was ensured through regularly spaced metal electrodes along multiconductor cables vertically buried inside drill holes. Thermistors located at the same depths yielded a temperature profile in the ground. In conjunction with these measurements, a weekly core sampling program allowed a visual description of soil cryostructures. In addition, unfrozen water and ice contents of frozen ground were directly measured in the field using adiabatic calorimetry to define the relationship between the physical properties of frozen ground and electrical resistivity values. It was observed that the active layer thaw and permafrost warming induce variation in the physical properties which can be detected by resistivity measurements. The numerical analysis of the results provided correlations between the parameters of the silty permafrost and the measured resistivity and temperature values. Thus, the variations of apparent resistivity with time at various depths can be used to predict parameters such as unfrozen water and ice contents of the frozen ground. Apparent resistivity logging can therefore be used to monitor changing permafrost conditions caused by climatic variations or man-made disturbances.