Stochastic Analysis of Levee Stability Subject to Variable Seepage Conditions

Abstract

Levee stability is highly influenced by seepage. Specifically, hydraulic conductivity distribution within a levee influences pore pressure distribution and controls the drained strength of the soil. In this study the influence of hydraulic conductivity and blanket layer thickness on failure probability is evaluated within the context of reliability analyses that also include soil strength and unit weight as random variables. First-Order Reliability Method (FORM) is used to evaluate reliability, rank random variables by importance and to obtain sensitivity of the solution to each random variable and its distribution parameters. Stability is computed using Spencer's method of slices coupled to a finite element seepage code to directly evaluate pore pressure. In addition, response surface method solutions are compared to the direct reliability solution to assess response surface accuracy. The results show that blanket layer thickness is more important than most strength parameters and that the uncertainty in hydraulic conductivity is less important to the variance in safety factor for the case of a low-permeability blanket layer. Numerical challenges caused by implementing a finite element limit-state function are discussed. Response surface methods are found to give a reasonable approximation to the direct reliability solution when the design point is between response surface fitting points.

Enriching flood risk analyses with distributions of soil mechanical parameters through the statistical analysis of classification experiments

“… a Recommendations based on Lanzafame et al (2017), Löfman and Korkiala‐Tanttu (2019) and Uzielli et al (2006). …”

Global Sensitivity Analysis of Groundwater Related Dike Stability under Extreme Loading Conditions

“…Despite their importance for dike stability and the valid assumption that they are heterogeneous, these two subsurface parameters are often partly unknown. As such, extending this research with variable material properties [11] may provide an even more extensive analysis of groundwaterrelated dike stability. In this way, the uncertainty of the material properties can be assessed too, which is important in real-world cases.…”

“…Research on a single case [8] was often also focused on the effect of artificial reinforcements [9,10]. Attempts including a local sensitivity analysis investigated the influence of material properties [11] or geometry [12] on the stability of embankments. In sum, none of these previous studies conducted a full analysis that considers both variations in hydrological parameters as factors influencing the stability of a dike.…”

“…Hydrological models have seen a similar rise in interest for global sensitivity analysis, both from a methodological point of view [21][22][23] and for analyzing geo-hydrological systems [24] and slope stability uncertainty [25][26][27]. Though some attempts have been made to analyze the global sensitivity of dike stability based on the uncertainty in its internal characteristics [11,25], no complete sensitivity analysis covering both geometrical as subsurface characteristics has yet been made.…”

Reliability analysis of the influence of seepage on levee stability

“…Hydraulic conductivity ratio is defined as K r = K a,h /K b,v ; thus, for a particular value of K r infinite combinations of K a,h and K b,v are available and only one set must be selected as parameters to specify in the finite-element method (FEM) seepage model. However, the seepage solution is insensitive for K r less than about 50 for the model levee considered herein (Lanzafame et al, 2017), and for a given K r , the value of K b,v is chosen such that K a,h = 8 × 10 −5 m/s. K is anisotropic (K h = 4 K v ) for the blanket layer and isotropic for the embankment and aquifer soils.…”