LABORATORY WORK ON FREEZE-BONDS IN ICE RUBBLE, PART Ⅱ: RESULTS FROM INDIVIDUAL FREEZE-BOND EXPERIMENTS

摘要

Small-scale laboratory experiments on the strength of individual freeze-bonds have been performed in the cold laboratory at NTNU. The experimental set-up is explained in Part I of this article. The experiments investigate the freeze-bond strength in relation to the following factors: a) contact surfaces; natural top/bottom and sawn surfaces, b) crystal orientation, c) ice block salinity, d) time - temperature history of the ice blocks, e) assembly conditions, f) piston velocity and g) submersion basin temperature. Freeze-bond strengths in the range of 1.9 to 118.3 kPa were measured. Strongest freeze-bonds were formed between two natural bottom surfaces, while the weakest freeze-bonds were formed between two sawn surfaces. Two crystal directions were tested for the samples with sawn contact surfaces. Samples with the columnar crystals aligned perpendicular to the freeze-bonding surfaces gave highest freeze-bond strengths, samples with the columnar crystals aligned parallel with the freeze-bonding surfaces gave lowest freeze-bond strengths. A high initial salinity (in the range of 2 to 3.5 ppt) in the ice blocks gave stronger freeze-bonds compared to ice blocks with a low initial salinity (in the range of 0 to 1 ppt). An increased permeability of the freeze-bonding surfaces has been suggested to be a main contribution leading to the instances with the higher freeze-bond strength. Samples with sawn contact surfaces were both assembled in air and in water. Approximately twice the freeze-bond strength was found for samples assembled in water compared to samples assembled in air. Changing the time - temperature history of the ice blocks, the velocity of the force applying piston and the submersion basin temperature were not found to affect the freeze-bond strength.