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Experiments by Invited Researchers

 

Action of Ice Ridges on Subsea Production Systems

Project acronym: HyIII-HSVA-05
Name of Group Leader: Dr. Pavel Liferov, Norwegian University of Science
User-Project Title: Action of Ice Ridges on Subsea Production Systems
Facility: Large Ice Model Basin (LIMB)
Proceedings TA Project: Experimental studies of ice ridge loads on structures
Data Management Report: There is no Data Management Report available for this project

User-Project Objectives

Summary:

This report presents the preliminary results of a test campaign performed in November 2008 in the ice tank of
HSVA, Hamburg, Germany. The objective of the tests was to investigate the ice ridges actions on subsea
production systems and conical structures at the waterline with particular focus on measuring keel loads and
keel properties. The experiments were:

Ice ridge subsea structure and cone interaction: 4 ice ridges were tested, 2 “cold” and 2 “warm” at 2 interaction speeds. Load time series were recorded on 36 channels and synchronized with 10 video cameras, 4 of them underwater.
“Retaining wall” test: 7 tests were performed, maximum 2 per ridge. The loads exerted by a plate pushed into the rubble encased in a box open at its bottom side are recorded. This test provides controlled boundary conditions and good possibilities of video monitoring. It should therefore be more suitable than the standard punch test for numerical investigations of the rubble mechanical properties.
Oedometer test: 7 tests were performed, maximum 2 per ridge. The rubble is placed in a cylindrical box outside the tank and compressed with a piston. The load is applied cyclically to up to 25 kPa. The evolution of the yield stress of the rubble in function of its compaction is investigated.
“Rubble piling” test: 2 tests were performed. Ice blocks extracted from the ridge are piled on a board outside the tank. The repose angle of the pile is measured and then the board is tilted until the rubble fails. The slope angle at failure is reported as the “critical angle”.
Punch test: 7 tests were performed, maximum 2 per ridge. The standard procedure for punch testing in the ice tank was used. A 100 kg and 0.7 m diameter plate is lowered with a constant speed into the ridge, whose consolidated layer has been previously cut. The actions from the rubble on the plate are recorded.
Underwater videos were also recorded and it was attempted to track the keel bottom displacement.

The subsea structure interaction, retaining wall test, oedometer test, and rubble piling test are all new in the field of ice rubble mechanics. Other experiments were also performed to characterize the mechanical and physical properties of the level ice from which were built the ridges and the freeze-bonding strength between the ice blocks. The preliminary results show that the failure mode during the interaction tests is mostly a local failure, except in one case for the cone interaction where the ridge was separated from the tank walls and a global failure could be observed. The oedometer test shows that the rubble presents a behavior in compaction typical of loose soils.

In total four papers have been submitted for peer review to the organising committee of the 20th International Conference on Port and Ocean Engineering under Arctic Conditions 2009, June 9-12, 2009 in Luleå, Sweden


Retaining wall box in the ice ridge

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