Some geotechnical aspects of iceberg grounding

On Canada's eastern seaboard where hydrocarbon deposits have now been determined, the operational hazards are numerous. Damage by icebergs to installations on and in the ocean floor is one of the major threats. An understanding of the Interaction of an iceberg with the continental shelf surface sediment during the process of grounding is needed to establish safe design standards for bottom structures in offshore drilling operations. Knowledge of icebergs, their size, shape and drift, is still very limited and so is the engineering behavior of the surface sediment of the oceans. -- In this thesis, the behavior of an iceberg of idealized shape is analyzed while it grounds in a uniform slope of very weak and compressible sediment. An expression was derived for the theoretical size of the scour that could be caused and this was substantiated by laboratory experiments. -- A tiltable towing tank was fabricated in which a 9” wide plexiglass model of the idealised iceberg was tested. Forces and pressures on the model were measured during the process of its scouring into an artificially sedimented slope. The frontal soil resistance was found to be the predominanting force confirming the assumptions made. Soil failure was dominantly local. A soil front of about 5 feet was under compression during the gouging process and a similar phenomenon was also noticed below the maximum scour depth. About 30% of the pushing effort was computed to be lost in the compression. Observations in a small tank with 2” wide models confirmed the soil compression phenomenon and also led to a qualitative understanding of the effects of Iceberg shape. -- Scour sizes, computed and compared with reported side-scan observations off the Newfoundland coast showed that the predictions made by the analytical model are realistic