The picture above is from the quick clay slide in Kattmarka near Namsos in mid Norway, 13th March 2009. The whole area, about 250 m wide, with houses and dwellings slid out and were moved about 100 m to the sea. The slide was caused by blasting in connection with road work, seen in the far right of the picture. Luckily no persons were killed in this incident.
Quick clay landslides therefore develop very quickly and often over large areas, even in quite flat terrain. It develops retrogressively, which means it starts at the bottom and goes backwards in the terrain as the quick clay is overloaded when the clay below has collapsed. The landslide masses flow down along the terrain.
Clay particles are the most fine-grained sediments. In all areas with marine sediments, quick clay can occur. Quick clay landslides differ from ordinary landslides in that quick clay becomes almost liquid if it is overloaded or disturbed, and quick clay landslides thus develop quickly, can be very large and potentially have very serious consequences. Over the years, many large quick clay landslides have occurred in Norway, many of them with tragic consequences with the loss of many human lives and great material damage. The legislation therefore sets extra strict requirements for development in areas with marine sediments.
Quick clay slide in in Trøgstad, Norway, 1967
Mapping and assessment of mitigation measures
NGI has developed a methodology for identifying, as well as assessing the degree of danger, consequence and risk of landslides in areas with quick clay. Risk is the combination of the degree of danger (probability of a landslide) and the consequence if a landslide occurs. On behalf of the Norwegian Water Resources and Energy Directorate (NVE) and different municipalities in norway, NGI has mapped quick clay zones in many vulnerable areas of Norway. The results are presented in the form of maps displaying the degree of danger, consequence and risk of quick clay landslides.
In addition, NGI often asked to assist in acute landslide events in quick clay areas. NGI has been involved in several commissions for the investigation of quick clay landslides.
NGI performs the following services related to quick clay:
- Mapping of the degree of danger, consequence and risk of quick clay landslides
- Ground investigations and stability assessments
- Design and assessment of mitigation measures
- Assistance and advice related to acute landslide situations, including searches and acute hazard assessments for surrounding areas after landslides
- Courses and dissemination of knowledge to municipal authorities and other relevant agencies
- Investigation of landslide accidents and landslide incidents.
Research and development
Over many years, NGI has made extensive researched on the behaviour of quick clay, and has expertise in advanced numerical modelling of the stability of quick clay slopes and the development and course of quick clay landslides.
NGI's research and development related to quick clay landslides covers the following topics:
- Advanced models for material behaviour and numerical analysis and calculation of stability in quick clay and the dynamics and course and outlet distance for quick clay landslides
- Mapping, identification and quantification of the degree of danger, consequence and risk in areas that are potentially exposed to quick clay landslides
- Impact of climate change on soil landslides
- Development of methods for monitoring, warning and protection against avalanche danger.