Cody Cruz, Bradley P Lipovsky

The fracture properties of saline water ice play an important role in governing the mechanical behavior of sea ice, marine ice sheets, and icy planetary bodies. Here, we design a low-cost experimental system based on a simple observation: fractures form when freshwater is frozen in a plastic bag, but do not form when a small amount of NaCl salt (several g/L) is added before freezing. We attribute this brittle--ductile transition to the formation of a brine-filled pore space in the saline samples that inhibits the high water pressures required to generate hydrofracture. This interpretation is confirmed using in situ pressure measurements and dye tracing experiments. We develop a radially symmetric poroelasticity model where the freezing process is represented as a transformation strain. Together with experimental data, our model is able to constrain the sample permeability, which we find to at least 10^-14 m^2 for samples with an estimated porosity in the range of 0.02 to 0.06. Our work offers an explanation of the observation that accreted marine ice stabilizes the Antarctic ice shelves.