Ice interaction processes during ice encroachment

Abstract

Ice encroachment is the accumulation of ice atop a platform and results when ice drifts against a platform. Most often this occurs in shallow water but in principle can occur in deep water if the ice drift length is long enough. As the ice drifts against the platform it is broken and generates rubble and ice piles in front of the platform, and with sufficient drift duration blocks of ice can be pushed up and onto the platform. This must be taken into account when designing structures in the Caspian Sea and other shallow water areas where there is significant ice drift. Ice can encroach on the structure by ice ride-up and pile-up. Consequently, the height and extent of the ice piling up on top of the structures must be taken into account in designing the layout, and often a protective ice encroachment zone is made all around the structure. The aim of this paper is to provide an outline of various approaches and parameters to consider where ice encroachment may occur. The study is supported by analysis of dedicated ice model test data, numerical simulations using Discrete Element Models, and full scale data of ice encroachment events. The intent is to give an understanding of the physics of ice encroachment and support in the design of shallow water offshore structures. In particular, the results indicate the importance of ice strength in the process and especially the maximum pile height. If the ice is weaker, the pile grows horizontally in a seaward direction in front of the structure, and conversely, stronger ice forms ice encroachment with greater vertical and also horizontal extent on the platform. The results also show that once the maximum pile height is established subsequent drift enlarges the seaward extent of the rubble pile in front of the structure.