Reliability-Based Evaluation of the Effects of Geometry on Levee Underseepage Potential: Fid-Bau Portal

Reliability-Based Evaluation of the Effects of Geometry on Levee Underseepage Potential

Polanco, Lourdes / Rice, John

Levee foundations are often modeled in seepage analyses with simplified models consisting of layers having uniform thickness and soil properties. However, due to the complex geomorphic regime that is often encountered in the fluvial geologic environment, levee foundation geometry can range from simple to very complex. Variations in material properties within layers, in addition to layer thickness and continuity, affect the pore pressure and seepage regime and, in doing so, affect the potential for internal erosion of the foundation soils. A study has been performed to assess the effects of subsurface geometry on the reliability of levees with respect to underseepage related internal erosion. Reliability-based internal erosion analyses have been performed on eight hypothetical levee profiles using two analytical methods. The First-Order Second-Moment - Blanket Theory (FOSM-BT) method applies a simplified reliability assessment technique to the US Army Corps of Engineers (USACE) "Blanket Theory" equations. This method requires that the analysis profile be simplified to meet the requirements of the equations and places limitations on how the uncertainty of the various input parameters is modeled. The more complex Response Surface-Monte Carlo (RSMC) simulation method is capable of modeling more complex geometries and multiple failure modes and is flexible in how uncertainty of the various input parameters are modeled. The results of the two methods are compared to evaluate the effectiveness of the FOSM-BT in evaluating internal erosion potential in increasingly complex levee foundation conditions.