Influence of spatial variability of shear strength parameters on reliability-based assessment of dykes

The Dutch dyke network includes 14,000 km of regional dykes that are regularly assessed in order to reduce the risk of flooding. The current strategy for maintenance and/or upgrading of existing dykes is based on safety assessments using partial factors and reliability-based characteristic values of material properties, interpreted from Eurocode 7 (EC7). In this paper, an historic dyke in the Netherlands has been analysed for stability using two methods: (a) based only on the point statistics of the material properties, as is widely adopted in Dutch practice based on a simplified interpretation of EC7, and (b) based on both the point and spatial statistics of the material properties, using a probabilistic approach in line with the full requirements of EC7. The results of safety assessments by the two methods show that a consideration of the spatial variability leads to a narrower range of possible responses, and thereby to a higher computed factor of safety at the target reliability of 95%. Moreover, for the dyke section considered, it results in much reduced remedial action compared to that suggested as a consequence of using the simplified approach, and thereby to a more economic design and reduced environmental impact.