The Netherlands is protected against major floods by a system of primary flood defenses (levees, dunes and hydraulic structures). These must comply with standards defined in terms of maximum allowable probabilities of flooding. Therefore, a new assessment framework for the main failure mechanisms is based on a probabilistic approach. One of the failure mechanisms which is not yet following such a probabilistic approach is instability of the outer slope of a levee. This failure mechanism is of importance after a rapid water level drop after a high-water event. In such an event, the pore water pressures in the levee are still high, and if an instability happens flooding can occur when (1) there is no time to take emergency measures before a second high-water event follows and (2) there is insufficient residual strength to prevent flooding during this consecutive high-water event. Levee reinforcement projects in the Netherlands allocate significant resources to resolve the presumed lack of safety of the levee due to the outer slope instability mechanism. Hence, this paper discusses how outer slope stability safety can be assessed probabilistically. A failure due to outer slope instability depends, besides the characteristics of the levee, on the peak water level, the water level drop velocity, the inter-arrival time between two consecutive high-water events and the time needed to take emergency measures. In this paper, a framework based on event trees is presented, using Intensity-Duration-Frequency-curves to include the time dependent statistics of the water level drop. This is a novel approach for outer slope instability in the Netherlands and results in less conservatism in assessments and designs, and therefore less required resources to mitigate the mechanism.@en

Built environments developed on compressible soils are susceptible to land deformation. The spatiotemporal monitoring and analysis of these deformations are necessary for sustainable development of cities. Techniques such as Interferometric Synthetic Aperture Radar (InSAR) or predictions based on soil mechanics using in situ characterization, such as Cone Penetration Testing (CPT) can be used for assessing such land deformations. Despite the combined advantages of these two methods, the relationship between them has not yet been investigated. Therefore, the major objective of this study is to reconcile InSAR measurements and CPT measurements using machine learning techniques in an attempt to better predict land deformation.

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Dikes in the Netherlands are by law required to comply with predefined safety standards. The goal of this paper is to derive the safety format and the required factor of safety for the inner slope (landside slope) instability failure mode. The first step is to derive the required target reliability for a cross-section. The second step is to derive a safety format in which all uncertain variables in the slope stability computation are identified and accounted for by sufficiently safe parameters estimates. The third step is to derive the relation between target reliability and required factor of safety. This is done by evaluating 48 test cases. For each test case, the factor of safety is computed based on the safety format, as well the corresponding reliability index. This paper shows how to derive a required factor of safety based on a predefined target reliability. However, the spread in this relationship is significant. Hence, a full probabilistic analysis would lead to more accurate slope stability assessments.@en

Dikes and levees play a crucial role in flood protection. The main causes of levee failures are of geotechnical nature. Geotechnical failure modes are also the main contributors to the probability of failure of flood defenses such as levees due to the large uncertainties in ground conditions. Hence, information on ground conditions and soil properties is crucial in safety assessments and retrofitting designs of levees. The experience in practice with designs and risk assessments is that even with a substantial amount of site investigation and laboratory testing the uncertainties in soil properties often remain large. One way to further reduce uncertainties is to include past performance information. The present papers shows how information of survived loads in the past can be incorporated in reliability assessments by means of Bayesian posterior analysis using the same (physics-based) performance models as the prior reliability assessments. The incorporation of survival information leads to reduced uncertainties and probabilities of failure. Furthermore, an approximate approach using fragility curves is proposed, mainly to make problems with computationally expensive performance functions tractable. After briefly recapping Bayesian reliability updating, we provide examples for slope stability of (flood protection) dikes. The examples illustrate that posterior analysis enables us to reduce the large prior uncertainties in soil strength parameters by "eliminating" implausible samples or regions of the joint PDF of the strength properties using the evidence of survived load conditions (i.e. water levels). The results suggest that the effect of updating the probability of failure with survival evidence can be considerable, especially when the uncertainty in the strength properties dominates the reliability. Dominant strength uncertainties are rather typical in geotechnical engineering, as opposed to, for example, structural engineering, implying that using the method is promising also for other geotechnical applications.

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The Dutch design codes for the dikes with retaining walls rely on Finite Element Analysis (FEM) in combination with partial safety factors. However, this can lead to conservative designs. For this reason, in this study, a reliability analysis is carried out with FEM calculations aiming to demonstrate the feasibility of reliability analysis for a dike with an anchored sheet pile wall modelled in the 2D FEM, Plaxis. Sensitivity and reliability analyses were carried out and enabled by coupling the uncertainty package, OpenTURNS and Plaxis. The most relevant (ultimate) limit states concern the anchor, the sheet pile wall, the soil body failure (global instability) and finally the system. The case was used to investigate the applicability of the First Order Reliability Method (FORM) and Directional Sampling (DS) to analysing these limit states. The final goal is to estimate the probability of failure and identify the most important soil properties that affect the behaviour of each component and the system as a whole. The results of this research can be used to assess and optimize the current design procedure for dikes with retaining walls.@en