Actions from landfast Ice on coastal Erosion Protection in the van Mijenfjord, Svalbard
MetadataShow full item record
The geobag embankment constructed at Kapp Amsterdam is part of an ongoing research by SINTEF related to exploration of suitability for use of geobags for coastal erosion protection in the Arctic.Erosion rates in the Arctic are often high and the lack of proper local masses for erosion protection creates the need for alternative solutions. The actions on the embankment caused by the surrounding ice need to be mapped whereas theyc onstitute one of the important features related to Arctic environments, alongside permafrost. It is of essential importance for the functionality of the geobags that the problems caused by the ice are manageable. Field work was performed at the site to gather data on features that influence actions from ice, including physical and mechanical properties. Some laboratory work was also included for supplemental measurements. The months of February to April were spent on the landfast ice sheet for data collection and monitoring of developments in the surrounding ice. During the field work,help was provided by more experienced PhD-students. The investigations focused especially on tidal influence. This involved investigating for any difference in the zone of tidal influence, called the hingezone, compared with the level ice zone further out. The peak level ice thickness during February to April was 0.67 m. Stefan’s law failed to predict the ice thickness growth. A coefficient of 0.14 had to be used to fit the observed growth. This is lower than for previous years which have indicated a coefficient of 0.3-0.4 (Høyland, 2009). Variations in horizontal compressive strengths of the ice were measured in both the level ice zoneand the hinge zone. The maximum compressive strength measured was 5.3 MPa which was for the level ice. The highest strength found in the topmost part of the hinge zone was 2.0 MPa. Lowertemperature and salinity would indicate higher strength in the hinge zone, but high porosity seemsto counter this. 3 days of horizontal stress measurements in the ice on both sides of the upper tidal crack in the hingezone gave a maximum value of 100 kPa in compression, occurring on the sea side. The results from the land side gave negative values, indicating that there was mainly tension on this side. Fluctuations of about 25 kPa on both sides correlated clearly with tide. Other stress constituents as thermal expansion or drag forces were not identified. The vertical positions of 5 points from the level ice and up through the hinge zone were measured during half a tidal cycle. The free floating level ice was displaced 0.74 m which correlated with the estimate of fluctuation in water level from the Longyearbyen tide table, taken from Caline (2010).Expectedly, displacements of the ice further into to hinge zone decreased with decreasing distance from land. The pattern of cracks formed in the hinge zone stayed relatively unchanged during the period of observations, indicating relation to tidal movement. Applied theory based bending of the ice sheet due to fluctuations in water level, overestimated the distances between the major cracks by around 50-75%, indicating that the ice was weaker than assumed in the input parameters for the calculations. The obtained field work results have been compared with results from previous work. Theory from relevant literature has also been applied when available, though the work of this has crossed the intersection between land and sea making it challenging to find specific literature for support. Nevertheless, sampling and in-situ measurements have proved valuable results. These have made up a substantial foundation for assessment of the significance related to influence from ice actions. It seems that the landfast ice cover constitutes a small load on the embankment as the ice breaks from creep. However, the periods of ice build-up and break-up may cause another problem than what is monitored and analyzed here. The problem relates to bag rupture from free floating pieces ofice periods of ice build-up and break-up, as experienced by Gadd (1980). Bag rupture is regarded asgreater concern than displacements. Regarding overall stability the results indicate that ice actions are less of a problem compared withwave forces and stability issues related permafrost soil.