Design of Self-Stabilizing Ice Barrier

Abstract

Ice barriers installed in close vicinity to offshore platforms are designed to take the main loads resulting from floating ice by breaking the ice and piling-up the rubble ice. Platforms and equipment protected by ice barriers can be dimensioned considering only low ice loads and can thus be constructed more economically. Also, the safety of the platforms increases. One objective of the research project MATRA is to design suitable ice barriers for exploration and oil production in ice-covered, shallow-water areas. Several concepts were investigated, e.g. vertical and inclined piles as well as barges equipped with piles. Model tests were carried out under varying conditions in order to evaluate the design alternatives and to provide the design loads resulting from floating ice. The most suitable structure is a light-weight ice barrier with an inclined roof structure mounted on a barge which collects early, thin ice inside the structure, stabilizes itself by the piled-up rubble ice and by this later can withstand thicker ice. The measured loads were analysed and compared with loads theoretically derived from existing approaches. At the first stage, when the structure fills with ice, bending is the dominant failure mode. Once a rubble pile has built-up in front of the structure, other failure modes may become significant comprising buckling and crushing. The load-time curve shows a scattering behaviour and has very high load peaks of short duration, especially for thick ice. The analysis comprises a statistical evaluation of the loads, taking the site conditions in the Caspian Sea as reference. Design loads for different load-cases were derived, which are the basis for the stability analysis of the ice barrier. On the basis of the results of the stability analysis and considering the requirement that the structure shall be self-floating for transport, the structure was optimized and the detail design was carried out.