Ice pile-ups or rubble fields may form due to the interaction of Arctic offshore structures with sheet and ridge ice formations. Interaction parameters favoring the formation of pile-ups include sufficient driving force to fragment ice formations adequate generalized flexibility to permit the necessary movements, and sufficiently large structural breadth to preclude clearing of ice fragments. The creation of pile-ups around offshore structures can have a significant influence on associated ice-structure interact ion forces. This influence can be one of force magnification or reduction, depending on certain ice pile-up and interaction characteristics. The ability to predict ice pile-up loading and load transfer characteristics will facilitate design of Arctic artificial islands, platforms, jetties, and other large structures with the potential to generate pile-ups under appropriate ice-structure interaction conditions.
In this paper, following a general review of the basic concepts published by the authors and others in the area of rubble pile formation and force transmittal, extensions of the theory are presented and results are compared with previously published work. The extensions include the incorporation of heretofore unpublished probability density functions to represent slope angles of individual ice pieces idealized through the use of multi-modal failure theory.
A significant dependence of interact ion load on the properties of the probability density function is found. In addition, the effect of pile-ups on ice structure interaction loads is evaluated utilizing techniques based on the theories of granular and cohesive media to evaluate ice pile-up load capacities and load transfer characteristics. Numerical results are generated and compared with relevant related theories.
Ice pile-ups or rubble Fields (Figure 1) may form due to the interaction of ice formations with Arctic offshore structures. Interaction parameters favoring the formation of pile-ups include sufficient driving force to fragment ice formations, adequate generalized flexibility to permit the necessary movements, and sufficiently large structural breadth to preclude clearing of ice fragments. In the process of pile-up formation, the parent ice sheet generally fails in More than one failure Mode simultaneously. The two most predominant failure Modes are flexure and crushing, although other failure Modes such as buckling and shear may also occur. The method presented herein considers only the flexural and crushing failure modes, but could be extended to incorporate any desired number of failure Modes in accordance with the general theory presented by Bercha. 7
The interaction phenomenon between the structure and integral ice formations such as sheets and ridges is significantly complicated by the presence of icepile-ups between the ice formation and the structure. Numerous investigations have been carried out on the "pure" 100de or rubble-less ice-structure interactions3, 10,ll,12.. However, only limited attention has been directed to the "non-pure" mode of interaction. The major difficulty in quantifying pile-up characteristics is the highly stochastic nature virtually necessitating resort to Monte Carlo or probabilistic modeling to realistically describe the interaction.