EurOCEAN 2000 - Vlaams Instituut voor de Zee

INTRODUCTION
VALIDATION OF LOW LEVEL ICE FORCES ON
COASTAL STRUCTURES
Joachim Schwarz
Coastal structures in northern and central European waters as well as offshore structures for
exploration and production of hydrocarbons from the European Arctic have to be designed to
withstand the forces applied by moving ice. Ice forces govern the design in most cases where
ice is present. The largest ice forces are caused by pressure ridges and by level and rafted ice
on vertical structures.
About these ice forces there exist an extraordinary uncertainty between the prediction by
scientists around the world; the predictions scatter by a factor of 10 to 15.
This situation as well as indications that the forces are indeed smaller than predicted by most of
the scientists have stipulated a group of seven research organizations from six countries in
Europe to propose a R+D-project to the European Commission for funding within the MAST
III Programme. The proposal was accepted and the project started in August 1997.
The project consists to two main research areas:
- Field test on ice forces against a lighthouse in the northern Gulf of Bothnia and the
determination of ice thicknesses and the mechanical properties of the respective ice
(level ice and ridges).
- Development of numerical methods to predict these ice forces.
PROJECT METHODOLOGY
FIELD MEASUREMENTS AND NUMERICAL MODELLING
The ice force measurements in full scale were carried out in two winters (98/99 and 99/00) at
the lighthouse Norströmsgrund which is located in the Gulf of Bothnia close to Lulea/Sweden.
This lighthouse was chosen because the vertical concrete shaft (7 m diameter) had earlier been
equipped with a multigonal steel belt at which ice force measuring panels could easily be
mounted. Nine ice force measuring panels (1.65 m x 1.25 m) were specially designed,
manufactured and mounted to the lighthouse in 1998. One of those panels consisted of eight
small triaxial load cell panels (0.4 m x 0.5 m each) in order to determine the effect of the
surface area interacting with the drifting ice. The panels were mounted half way around the
lighthouse directed to ENE. The ice thicknesses were measured by a sonar device which was
located at the bottom of the lighthouse foundation in 7 m water depth several meters infront of
the vertical shaft. As redundancy for the sonar ice thickness measuring system an EM-log plus
laser distance meter was installed in 1999 hanging 2.0 m above the ice infront of the
lighthouse.
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