Summer Ice Floe Impacts Against Caisson-Type Exploratory and Production Platforms

Summer impacts of large ice floes against arctic offshore platforms are likely to be a governing condition for the global foundation stability in medium and deep-water offshore platforms in the Alaskan Beaufort Sea. Some features of the impact phenomenon are illustrated by analyzing two vertically faced caisson-type gravity platforms. The two structures differ in their function, size and environmental exposure: the first is a smaller exploratory drilling caisson while the other is for production of oil and gas. Both structures are assumed to be in 30 m of water. A description of the analysis techniques is given: it is based on a dynamic modeling which considers the effects of inertia, damping, foundation compliance and slippage at the base in addition to a crushing failure mechanism in the ice at the contact area. Comparisons are made between the structural response computed for both the exploratory and production platform and for typical “soft” and “firm” site conditions. A discussion as to the relative importance of various design and modeling parameters is presented. The comparison of response characteristics of the assumed structures provides some insight for the purpose of formulating rational design criteria with regard to ice floe impact.