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Finite element modeling of backward erosion piping
Robbins, Bryant A.
Robbins, Bryant A.
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2022
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Abstract
Backward erosion piping (BEP) is a type of internal erosion that has caused the failure of many dams and levees and continues to threaten the safety of existing infrastructure. To manage this threat, failure risks are regularly evaluated to prioritize risk reduction measures. Unfortunately, current practice for assessing BEP is limited to simple calculation rules that have large uncertainty and error. While numerical models have been developed for simulating BEP, ambiguity regarding the erosion constitutive model, inconsistencies in the assumed physics, and lack of laboratory tests for measuring model parameters have made it difficult to validate tools for use in practice. No validated, widely accepted model for BEP exists today.
This thesis develops and validates an approach for finite element modeling of BEP by introducing the concept of the critical secant gradient function (CSGF). The CSGF provides a spatial function of the hydraulic gradient upstream of the pipe tip. An analytical expression for the CSGF and a laboratory test for measuring the CSGF are developed. A steady-state finite element model for simulating BEP progression is then developed for both two- and three-dimensional domains. The model and CSGF concept are validated through hindcasting of BEP experiments. Remarkable agreement was obtained between the finite element predictions and the experiments despite the experiments having different scale, configurations, and boundary conditions. These results indicate that the CSGF may provide the needed link between theory, lab testing, and numerical models to reliably predict BEP progression in practice. Additionally, the results indicate that the steady state finite element algorithm proposed is capable of adequately describing the BEP process, and more complex models may not be necessary.
After developing and validating an approach for finite element modeling of BEP progression, the remainder of the thesis demonstrates techniques that can be used to simulate BEP in practice. The use of adaptive meshing is demonstrated in two-dimensions as a means of efficiently simulating BEP progression for field scale problems. Additionally, the random finite element method is applied to demonstrate how to incorporate spatial variability in soil properties into BEP predictions. The results of this study demonstrate how both techniques, in conjunction with the CSGF, offer the potential for transformative improvements in the engineering practice of risk assessment of dams and levees susceptible to BEP progression.
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