EurOCEAN 2000 - Vlaams Instituut voor de Zee

• Ice Forces
Ice forces have been measured at the
lighthouse in two winters. In 1999 approx.
500 MB raw data were recorded during 60
ice force events (ice-structure interactions)
(Table 1). Unfortunately in mid March ’99
some of the electronic cables of the ice load
panels were ruptured by ice (cable
protection channel was destroyed). After in
summer 1999 the measuring equipment was
repaired, in winter 2000 approx. 3GB data
were recorded with all eight large and eight
small panels working well. Time records of several ice force panels are shown in Fig. 1. The
ice-structure interaction was covered by time lap video cameras over 600 hours. Ice thicknesses
were recorded by sonar and by EM-log (Fig. 2).
Even though the raw data are still being processed and analyzed the following results and
conclusions can be drawn:
(1) The largest level ice forces did occur when the ice cover had a large extent creating the
confined state of stress within the ice. In this case the ice failed in crushing starting with
horizontal splitting (cleavage) in the middle of the thickness. This was observed earlier by
Hirayama et al. [1974 ] in laboratory tests and will be considered by the relevant numerical
model.
(2) A further criterion for maximum ice forces is the simultaneous failure of the ice over a
large area. This happened after the ice cover had been stopped and a static load could
create a close contact between structure and ice (nearly 100%) due to plastic deformation.
When in this case the static load increased until the ice cover failed at the lighthouse,
maximum total ice forces were measured due to simultaneous ice failure at several panels.
A dependency of effective ice pressure on the area/width of the structure has been
obtained.
(4) The effect of the strain rate (ice velocity) on the ice load has been identified (lower ice
loads at higher velocity).
(5) Unconsolidated pressure ridges did cause only a slight increase in the ice load.
Numerical Modelling
• Ice Structure Contact Model
VTT in cooperation with the State University of St. Petersburg have developed a 2-D model to
simulate the splitting process at the ice edge including horizontal cleavage cracks and
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