1971 Lower San Fernando Dam, Upstream Flow Slide
Incremental Momentum Analysis Progression Animation
From Weber (2015), as updated in Weber et al., (2021)
Background
The Lower San Fernando Dam (LSFD) upstream flow slide was back-analyzed using the incremental momentum analysis method (Weber, 2015 and Weber et al., 2021) to evaluate the post-liquefaction residual strength (Sr) of the hydraulic fill within the dam’s upstream shell. The incremental momentum method was developed to provide a more accurate and reliable means of incorporating momentum effects in the back-analysis of liquefaction failures for determination of Sr. Acceleration, velocity, and displacement of the slide mass centroid are tracked as the failure mass slides from a condition of initial instability to a final resting geometry through this method. The initial and final geometries of the analyzed cross-section were developed based on Cross-Section E-E’ from the original forensic analysis (Seed et al., 1973) and subsequent evaluation (Castro et al., 1992). The intermediate cross-sections were developed under the constraining condition that the initial geometry is required to progress in a reasonable manner where mass is conserved at each subsequent increment until the final geometry is achieved.
The animation below is presented as a demonstration of the incremental momentum analysis method as applied to back-analysis of the LSFD upstream flow slide. The upper figure presents the movement of the slide mass with its centroid denoted by a crosshair marker, and the lower figures present the calculated progression of the acceleration, velocity, and displacement of the slide mass centroid at each time step for a converged solution. Viewers are encouraged to “play” the animation a number of times to get a sense of the estimated progression and mechanics of the LSFD upstream flow slide.
References
Castro, G., Seed, R.B., Keller, T.O., and Seed, H.B. (1992). “Steady-state strength analysis of Lower San Fernando Dam slide.” Journal of Geotechnical Engineering, ASCE, 118(3), 406-427.
Seed, H.B., Lee, K.L., Idriss, I.M., and Makdisi, F. (1973). “Analysis of the slides in the San Fernando Dams during the earthquake of Feb. 9, 1971.” Earthquake Engineering Research Center 73-2, University of California, Berkeley, Calif.
Weber, J. P. (2015). “Engineering Evaluation of Post-Liquefaction Strength.” A dissertation submitted in partial satisfaction of the requirements for the degree of Doctor of Philosophy in Engineering – Civil and Environmental Engineering in the Graduate Division of the University of California, Berkeley.
Weber, J. P., Seed, R. B., Pestana, J. M., Moss, R. E. S., Nweke, C., Deger, T. T. and Chowdhury, K. (2021). “Engineering Evaluation of Post-Liquefaction Shear Strength.” U.C. Berkeley Geotechnical Research Report No. UCB/GT-0x/2021, August.
Notes on Controlling the Animation Below
To advance or retreat the slides below, the following methods can be used:
- The arrows buttons located on the left (retreat) and right (advance) side of the animation slides,
- The left and right arrow keys on your keyboard,
- Clicking a particular bullet on the bullet bar below the animation will direct you to the associated slide, and
- Swiping left or right if using a touchscreen/mobile device.
1971 Lower San Fernando Dam Upstream Flow Slide
Incremental Momentum Analysis Animation
