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

[1] RutledgeP D. Cooperative Triaxial Shear Research Program. Progress Report on Soil Mechanics Fact Finding Survey. USACE Waterways Experiment Station, Vicksburg, MS, 1947

[2] DuncanJ M, WrightS G, WongK S. Slope stability during rapid drawdown. In: Proceedings of the Seed Memorial Symposium. BiTech Publishers, Ltd, Vancouver B C, 1990, 2: 235-272

[3] VandenBergeD R, DuncanJ M, BrandonT L. Rapid drawdown analysis using strength reduction. In: Proceedings of the 18th International Conference on Soil Mechanics and Geotechnical Engineering. Paris, 2013, 829-832

[4] WahlerW A, . (1970). Upstream slope drawdown failure investigation and remedial measures, Pilarcitos Dam, Report to the San Francisco Water Department, June 1970, as cited in Duncan et al. (1990)

[5] WongK S, DuncanJ M, SeedH B. Comparison of methods of rapid drawdown stability analysis, Report No. UCB/GT/82–05, University of California, Berkeley, December 1982 – revised July1983

[6] SkemptonA W. The pore pressure coefficients A and B. Geotechnique, 1954, 4(4): 143-147

[7] WongK S. And DuncanJ. M. Hyperbolic Stress-Strain Parameters for Nonlinear Finite Element Analyses of Stresses and Movements in Soil Masses. Report No. TE-74–3. University of California, Berkeley, CA, 1974, 90

[8] SkemptonA W, BishopA W. Chapter X – Soils, Building Materials, Their Elasticity and Inelasticity. ReinerM, WardA G, eds. Amsterdam: North-Holland Publishing Co. 1954, 417-482

[9] LaneP A, GriffithsD V. Slope stability analysis by finite elements. Geotechnique, 1999, 49(3): 387-403

[10] VandenBergeD R. Total stress rapid drawdown analysis using the finite element method. Dissertation for the Doctoral Degree. Blacksburg: Virginia Tech, 2014 (in Press)

RIGHTS & PERMISSIONS

Higher Education Press and Springer-Verlag Berlin Heidelberg