The Analytical Challenge

Earth dam failure is an important issue engineers must consider during reservoir filling. Factors such as internal erosion and piping occurrences caused by seepage can lead to dam failure, resulting in a disaster. The initial slope stability of earth dams and levees must also be performed such that the risk of slope failures is minimized. Analytical challenges include i) ensuring fine enough mesh to properly determine exit gradients, ii) proper definition of boundary conditions for rapid drawdown scenarios, iii) 3D solutions of earth dams in valleys, and iv) coupled seepage and slope stability analysis in 2D/3D.

The SVOFFICE™ Solution

The complete solution for the analysis of earth dams and levees involves a number of related numerical analyses. The most prevalent of these are:

  • Slope stability analysis
  • Seepage analysis

SVSLOPE® is the most comprehensive tool currently available for the analysis of levee stability. It analyzes slope stability from a stress-based or limit equilibrium approach and implements advanced features such as:

  • 3D analysis of slope stability and seepage
  • Mesh refinement to handle zones of high gradient
  • Advanced probabilistic analysis with the APEM method
  • Combined seepage and slope stability analysis possible using SVSLOPE® and SVFLUX
  • Rapid drawdown by the total (Duncan 3-stage), or effective stress method
  • Most advanced representation of the upstream seepage boundary condition

Seepage analyses (SVFLUX™) are an important tool for assessing the possibility of seepage failure in dams and studying hydraulic conditions for then calculating the stability of earth dams. SVSLOPE® may be used to calculate the stability of levees and earth dams under unsaturated conditions, with fluctuating water tables, and under rapid drawdown scenarios. The stresses (and potential deformations) encountered in earth dams may also be modeled using the SVSOLID™ software. Finite element scenarios may be evaluated in 2D or 3D.

 

  • Problem
    Pore-water pressures can build up in earth dams and embankments during reservoir draw-down conditions. The ability of the soil to release pore-water pressures is slowed if the hydraulic conductivity of the material is low (i.e., for clays). The excess pore-water pressures can cause slope instabilities and subsequent failures. The analytical challenge is to model such a situation with i) a dense enough mesh to properly represent high gradients, and ii) proper boundary conditions.

    Solution
    SVOFFICE™ provides a combined seepage and slope stability solution with SVFLUX™ & SVSLOPE® which can analyze slopes in 2D or 3D. Multiple treatments of the draw-down boundary condition in SVFLUX™ allow for proper representation during draw-down conditions. SVSOILS™ allows selection of unsaturated material properties which significantly affect draw-down conditions. Automatic mesh refinement allows mesh density in zones of high gradients.

    Software Solutions
    SVSLOPE®, SVFLUX™, SVSOILS™, SVSOLID™, SVDESIGNER

  • Problem
    Dam designs require the analysis of the flow and stability conditions. Seepage should not exit the downstream face or else piping failure can occur. Coimplex cross-sections and thin filters can represent challenging conditions to solve numerically. Deformations need to be calculated during construction.

    Solution
    SVOFFICE™ allows combined seepage and slope stability solutions in both 2D and 3D. Complex cross-sections can be represented in the model by extrusions from 2D to 3D or by building complex non-regular 3D models using SVDESIGNER™. SVSOILS™ can provide estimates of unsaturated soil properties. Deformations during construction can be calculated using SVSOLID™ with a staged construction analysis.

    Software Solutions
    SVSLOPE®, SVFLUX ™,SVSOILS™, SVSOLID™, SVDESIGNER

  • Problem
    Design of cut-off dams primarily requires dissipation of pore-water pressures in flow underneath the dam. This is typically accomplished through installation of a vertical cut-off wall beneath the earth dam. Such cut-off structures create zones of high gradients at the base of the wall which must be managed with proper mesh refinement.

    Solution
    SVFLUX™ provides automatic mesh refinement as well as manual methods for refinement of the mesh beneath such earth structures. Such refinement options produce results of increased accuracy. SVFLUX™ models can provide solutions in 2D or 3D.

    Software Solutions
    SVSLOPE®, SVFLUX™, SVCHEM

  • Problem
    Construction of earth dams over foundations with soft clays can result in the loss of shear strength in the clay due to the inability of the clay to dissipate the pore-water pressures in time. If construction of the earth dam proceeds too rapidly the loss of shear strength can result in slope stability issues during or shortly after finishing of construction.

    Solution
    Consolidation under foundations may be modeled by a coupled SVFLUX™/SVSOLID™ solution. Staged construction options in the software also allow the construction stages to be modeled as a continuous sequence. The resulting pore-water pressures may be imported into SVSLOPE® in order to determine the resulting impact on the factor of safety (FOS).

    Software Solutions
    SVFLUX-GT™, SVSOLID-GT™, SVSLOPE®, SVDESIGNER

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