Offshore structures constructed in polar regions are exposed to the drift of ice which generates dynamic loads at the ice-structure interface. The intensity and the frequency of these loads are partially controlled by ice-structure friction. Cyclic friction tests between laboratory grown columnar ice and concrete plates were performed by using a direct shear box apparatus at -10°C. The contact conditions varied in the following ranges: normal stress from 25 to 800 kPa , pulling speed from 0.1 to0,55 mm.min-1, average roughness from 0 to 0.55 mm. Optical observations of the ice surface and measurements of the topography of the concrete plate were performed afler the tests. Our experimental results show the increase of friction with time, attributed to the maturation of the contact interface due to the viscoplastic deformation of ice. Friction laws are formulated which give the dependence of the initial and final friction coefficients on the conditions of contact. The optical observations show the micro-mechanisms involved at the ice-plate contact. They are as follows: viscoplastic deformation, adhesion, recrystallisation, grain boundary sliding, micro and macro-cracking. Viscoplasticity and adhesion appear as the main mechanisms responsible for the observed friction behaviour. Measurements of the plate surface topography* allowed to follow the evolution of the plate surface after each test. This underlines the wear process and leads to the quantification of the concrete wear rate. A theoretical study of friction completes the experimental work. It consists of a two-dimensional modelling of the contact problem. Viscoplasticity of ice and the ice-concrete adhesion are taken into account to calculate the friction coefficient. Despite tbe simplicity of the model, its results are consistent with the expeiimental results. The roles of viscoplasticity and of the ice-concrete adhesion are confirmed. Tbe influence of the plate topography on friction is also shown.
