The rate- and state- dependence of sea ice friction

Ice loading on offshore structures is often governed by the behaviour of granular ice flows around the structures. This behaviour is in turn governed by frictional interactions between ice floes. Observed stick-slip behaviour in ice friction suggests a dependence on slip history, which is not accounted for in current ice friction models. We propose, by analogy with results from rock friction, a rate- and state-model for ice friction. In this paper we present the results of a series of metre-scale ice basin experiments, in which we determine this rate- and state- dependence. We then propose a simple parameterisation which gives a general rate- and state- model for sea ice friction. The model suggests that when the slip rate increases, the ice-ice friction reaches a peak before decaying to some steady-state value. To assess peak frictional loading, therefore, the slip history must be considered as well as the current slip velocity.