Risk assessment for quick clay slides – the Norwegian practice

Abstract

The approach for the assessment of the risk associated with quick clay slides in Norway is a qualitative/semi-quantitative procedure developed as part of work for The Norwegian Water Resources and Energy Directorate. Slide areas are classified according to “engineering scores” based on an evaluation of the topography, geology and local conditions (to qualify hazard) and an evaluation of the elements at risk, persons, properties and infrastructure exposed (to qualify consequence). The risk score to classify the mapped areas into risk zones is obtained from the relationship RS = HWS × CWS, where RS is the risk score, HWS is the weighted hazard score and CWS is the weighted consequence score. The risk matrix is divided in five risk classes. Guidelines for the implementation of the risk matrix are administered by NVE. In practice, the approach is used to make decisions on required mitigation measures to reduce the risk. The approach is simple and makes room for engineering experience and judgment. For detailed regional planning, slope stability calculations need to be made. Methods for quick clay slide stability calculations taking into account the brittle behaviour of the material are under development. This chapter provides an illustration of this development work.