EurOCEAN 2000 - Vlaams Instituut voor de Zee

Ice compressive strength tests were carried out in the field as well as in the ice mechanics
laboratory of HSVA in Hamburg together with tensile strength and fracture toughness tests.
The ridge mechanical properties were determined by a specially designed shear apparatus,
consisting of a steel frame and a hydraulic punch piston, by which the unconsolidated ridge
material was pushed downward under water. These tests were carried out in ice ridges
embedded in landfast ice offshore Oulu.
Four different numerical modelling approaches have been established to predict the forces of
drifting ice against vertical structures:
- Dynamic ice-structure interaction model
RESULTS
482
- Fracture dynamics model
- Ridge load model
- Probability approach
1. Evaluation of existing ice force prediction methods
Published ice force data and the corresponding ice property data have been evaluated [Loeset,
S. et al., 1999]. Especially the ice force measurements at the Molikpaq structure in the Beaufort
Sea have been made available [Wright, B., 1999] and are part of the LOLEIF-reports. There
are several reasons for the wide scatter of ice force predictions identified. In some cases model
test data have been used to derive a prediction formula, in which case incorrect transfer
functions have been used to predict the forces in full scale from small scale tests. In other
cases, the forces have just been predicted by numerical modelling using assumptions on the
failure processes and criteria, which have proven to be not realistic (plastic limit analysis).
2. Field Tests
• Mechanical Properties of the Ice
The punch tests in ridges, where the consolidated upper surface was manually cutted, provided
information on internal shear angle and cohesion of fragmented ice [Heinonen, J., et al., 2000]
to be used in the numerical force predictions. The compressive and tensile strengths of the ice
gathered in the vacinity of the lighthouse Norströmsgrund are relatively high compared to
data published in literature. The reason for this result may be that the ice specimen were loaded
parallel to the long axis of the crystal columns. More data on ice mechanics, especially on the
fracture toughness are being analyzed in order to be used in numerical calculations of ice
forces.