Total stress rapid drawdown analysis of the Pilarcitos Dam failure using the finite element method

Abstract

Rapid drawdown is a critical design condition for the upstream or riverside slope of earth dams and levees. A new total stress rapid drawdown method based on finite element analysis is used to analyze the rapid drawdown failure that occurred at Pilarcitos Dam in 1969. Effective consolidation stresses in the slope prior to drawdown are determined using linear elastic finite element analysis. Undrained strengths from isotropically consolidated undrained (ICU) triaxial compression tests are related directly to the calculated consolidation stresses and assigned to the elements in the model by interpolation. Two different interpretations of the undrained strength envelope are examined. Strength reduction finite element analyses are used to evaluate stability of the dam. Back analysis suggests that undrained strengths from ICU tests must be reduced by 30% for use with this rapid drawdown method. The failure mechanism predicted for Pilarcitos Dam is sensitive to the relationship between undrained strength and consolidation stress.

Keywords

rapid drawdown / finite element / total stress / slope stability

References

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Acknowledgements

The author would like to thank Rocscience Inc. for the research licenses of Phase² and Slide used to perform the finite element and limit equilibrium analyses. The faithful support and encouragement of J Michael Duncan and Thomas L Brandon is also greatly appreciated. This work was funded by the Virginia Tech Institute for Critical Technology and Applied Science, the Virginia Tech Center for Geotechnical Practice and Research, and the Charles Edward Via Department of Civil and Environmental Engineering.

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2014 Higher Education Press and Springer-Verlag Berlin Heidelberg