Evaluation of pack ice pressure approaches and engineering implications for offshore structure design

A probabilistic model for ice forces on a caisson platform in the Beaufort Sea was used to evaluate two different approaches for describing pack ice pressure. The ridge-building equation in the ISO Arctic offshore structures standard was compared to a more recently derived exceedance curve (EC) approach. The results indicated that the EC approach yielded a wider range of pack ice pressures compared to ISO estimates; however, when these results were used to determine the ultimate ice force on the platform, the effect of the pack ice approach selected was minimal. The influence of floe size in affecting the pack ice pressure did not yield agreement amongst several data sets examined. Furthermore, the influence of adfreeze was examined but no definite relationship was quantified. The paper discusses the engineering implications of these results in the context of offshore structure design. When evaluating the ice loads at a candidate site for offshore development, relevant information on floe size distribution and pack ice thickness, concentration, and movement are required in order to assess the influence of pack ice pressure on design calculations.