A probabilistic approach to levee reliability based on sliding, backward erosion and overflowing mechanisms: Application to an inspired Canadian case study

Abstract

Improving protection against fluvial floods requires a better estimation of levee failure. We developed an assessment method of levee failure probabilities for sliding, backward erosion, and overflowing each represented by fragility curves. We tested two approaches to aggregate those fragility curves into a global fragility curve respectively using: an enveloping curve and Monte‐Carlo simulations. We implemented this approach to earthen levee reliability for several flood return periods to the Bow River in Calgary, Canada. We used limit equilibrium method to estimate the safety factor of the levee segment and Monte‐Carlo simulations to estimate sliding probabilities. We used Terzaghi's critical hydraulic gradient to estimate backward erosion failure probabilities. The estimation of overflowing probabilities required expert judgment. We discussed how the choice of the hydraulic gradient area and the consideration of a steady state or transient model impact backward erosion failure probabilities. The results showed for our study case that, even though the transient model is a closer representation of reality, the levee saturation parameter has little impact on hydraulic gradient values, by extension, on sliding and backward erosion failure probabilities. The Monte‐Carlo aggregated fragility curve is more realistic than the envelop curve of the failure mechanisms for an equivalent computation time.

Probabilistic analysis of backward erosion piping in an embankment dam considering the spatial variability of soil properties

“…The hydraulic parameters (Ks, θr, θs, α, n) adopted for the embankment and foundation are referred to Cho (2012). The soil parameters (specific gravity Gs and porosity np) that contribute to the resistance of backward erosion piping based on Terzaghi criteria (critical gradient icr) are referred to Mainguenaud et al (2023) (see Table 2). By simulating random samples of Gs and np according to the probability distribution shown in Table 2, it is possible to use Eq.…”

Fragility Analysis for Water-Retaining Structures Resting on Spatially Random Soil

“…Consequently, their application has been gaining increasing momentum in the field of risk assessment for various damage states of geotechnical structures, such as slopes, dams, and embankments (e.g., [1,5,[7][8][9][10][11]). To evaluate the reliability of a levee within a probabilistic framework, fragility curves are employed for specific mechanisms as functions of conditioning loads, such as water level or water discharge [8,[12][13][14][15].…”

Flood risks from failure of infrastructure

“…For several years, fragility curves have been used to assess the failure probability of flood defences when undertaking probabilistic flood risk assessments. In the third paper, Mainguenaud et al (2023) propose a probabilistic method to assess levee failure probability by integrating three failure mechanisms relevant to fluvial levees: sliding, internal erosion and overflowing. This aggregation of failure probabilities from the three mechanisms provides a single fragility curve to represent the failure probability and avoids making a biased interpretation of the results due to distinct fragility curves for the same levee segment.…”