Consulting Solutions: Earth Dam / Levee Seepage Modeling

 


Problem:

Many earth dams are analyzed with a 2-D numerical model even through the structure may be inherently 3-D in nature. There may be aspects of flow in the “wings” of an earth dam structure that are important to consider.

Levee analysis is becoming an increasingly important topic as the infrastructure ages. Many sections are in need of re-engineering improvements as consideration is given to their replacement. Concepts utilized in their original design are being re-examined. Many of these structures were designed 20 to 50 years ago, and the tools utilized in such analysis have changed significantly. Our understanding of the processes involved has also improved with time.

Solution:

A 3-D numerical flow model of an earth dam  provides valuable insight into the full 3-D flow regime which will be established once the structure is built. Design flaws can be identified early on and overcome.

Levee structures are typically three-dimensional in character. Early designs largely overlooked the potential influences of three-dimensional effects at the intersections of levees. In particular, there are seepage and flow issues at a levee intersection which are inherently 3D. The behavior of groundwater at such intersections may also be influenced by culverts, which may be opened during storm events. Thus, rapid drawdown effects may be created during the natural operation of such structures. Multiple questions may arise, for example from a 45-degree intersection or a "T"-type intersection:
  • What is the effect of "funneled" flow? Funneled flow can occur in the concave downstream side of a levee intersection, and its impacts on both seepage and slope stability can be numerically modeled.
  • How are gradients affected in a 3D flow regime? Can 3D regimes lead to piping failures, which may not be evident in a 2D analysis?
  • How is the factor of safety affected for a rapid drawdown analysis when analyzing the concave or convex side of a levee intersection?
  • How do operational scenarios such as opening a culvert affect the 3D analysis?
  • Are there flooding scenarios for which the 3D analysis will give different factors of safety than that of a 2D analysis?

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