28. Mapping Quick Clay Hazard Zones: Comparison of Methods for the Estimation of the Retrogression Distance

The Norwegian regional mapping of quick clay hazard zones uses a 1:15 inclined line from the foot of the slope to decide the maximal retrogression distance of a quick clay slide. When the hazard zones are subjected to a more detailed examination, the site investigations give a better picture of the location of the quick clay, which is decisive for what type of slide that may occur. Based on this, a method was developed through the research project “Natural hazards – infrastructure for floods and slides (NIFS)”. This has been applied to an existing hazard zone and compared with other existing methods to draw the depletion zone. The implementation shows the importance of first deciding the slide mechanism. If the extent of the quick clay is well mapped, the NIFS-method can be a useful tool to evaluate the retrogression distance, but it must be used with careful consideration of the geotechnical conditions.