Worst-Case Spatial Correlation Length for Exit Gradients in Spatially Random Soil during Steady Seepage

Soil properties can vary significantly within a given site, making geotechnical analysis highly amenable to a probabilistic treatment in which properties are described statistically. The random finite-element method (RFEM) is the only method available to properly account for spatial variability of soil properties and has been applied to numerous geotechnical applications. Of all the commonly encountered soil properties, permeability is generally considered to be one of the most variable. The current paper revisits steady seepage beneath a sheet pile wall of varying length in spatially random soil of finite depth, with a focus on the exit gradient. The spatial correlation length of permeability is shown to have a striking influence on the statistics of the exit gradient, with a pronounced worst-case spatial correlation length corresponding to the highest probability of downstream piping and erosion.