Mechanics of ice-structure interaction

The physical processes involved in the interaction of ice masses with offshore structures are described. For design purposes, two pressure-area relationships have been deduced, which take into account the randomness of data. The first is for local pressures. using ranked data from ship rams, resulting in a power-law decrease (similar or equal to -0.7) of pressure with design area. A second (global) pressure-area relationship with random parameters has been developed, also based on data from ship rams, with a power-law decrease (similar or equal to -0.4) of average global pressure with nominal contact area. Most of the force is transmitted through small areas termed "high-pressure zones". Observations at the medium scale indicate an extremely regular cyclic load variation in a high-pressure zone over several cycles. superimposed on less regular fluctuations. The regular cyclic activity is ascribed to dynamic activity within a layer of damaged ice adjacent to the indentor or structure, and the other reductions in load to spalling activity. The main processes in the layer are recrystallization accompanied by microfracturing near the edges of the high-pressure zones (low confining pressures), and recrystallization accompanied by pressure softening at high confinements. These processes have been reproduced in triaxial tests on polycrystalline ice., and simulated in a finite element niodel that incorporates damage mechanics. Fractures, spalls, and splits lead to the global reductions in average pressure. Models of flexural failure are compared to data; the results confirm the trend of measurements but further full scale calibrations are needed. (C) 2001 Published by Elsevier Science Ltd.