Integrated Risk Analysis Framework of Quick Clay Landslides in Norway

Abstract

Quick clay landslides have caused a large number of natural disasters in Norway. These have resulted in loss of human lives and major damage on property, roads, railways, and infrastructure. Quick clay acts as a fluid when disturbed or overloaded, and therefore affects large areas away from the triggering point. Extensive accumulations of quick clay are found in residential areas, where the socio-economic consequences of a landslide can be enormous. Consequently, it is important to identify, assess and manage this risk.

The purpose of this thesis is to develop a complete risk analysis framework to undertake the risk associated with quick clay landslides in Norway. Currently, such a framework is not existent. There only exists partial analyses and guidelines focusing on single parts of the risk analysis process, which were discovered through a thorough literature study. This thesis puts an emphasis on a uniform and systematic framework, that includes several risk analyses to determine the hazards, consequences and risk of a study area, and that is followed by risk assessment and management. The framework provides a simple approach to risk of quick clay landslides and contains room for judgement and engineering experience to be included.

Further, an empirical exemplification of this risk framework was performed on the Haugen quick clay zone in Kongsberg, to enlighten the usefulness of the risk analysis framework. For this purpose; map studies, geotechnical investigations, fault tree analysis and creation of a landslide database were carried out. Potential hazard zones are classified according to hazard, consequence and risk level. The evaluation was carried out using a semi-quantitative analysis developed by NVE. This approach classifies the study area utilizing “engineering scores” by evaluating the local conditions, which resulted in a low hazard and severe consequence level. The risk is the product between the hazard and consequence scores, and was categorized as medium. Based on these results, in addition to evaluations of triggering events, landslide extent and return period, a risk matrix and activity matrix was developed. These matrixes were used as a base to make decisions of the required mitigation measures and remedial activities to reduce the classified risk. The risk mitigation measures should primarily be focused of the stability conditions toward the river in the south of the Haugen zone. Secondary, a stabilizing fill should be considered along the river. Further research should be performed on the Early Warning System for monitoring of the quick clay slopes and triggering events.