Case History Studies of Lenihan and Austrian Dams under the 1989 Loma Prieta Earthquake

Dynamic responses of the Lenihan and Austrian Dams in the 1989 Mw = 6.93 Loma Prieta earthquake were analyzed using the finite element program VERSAT; undrained response of the saturated dam fills was modelled using a total stress approach. The two dams were constructed in the early 1950s and comprised primarily of compacted low plasticity clayey sands and clayey gravels. Subjected to estimated peak accelerations of 0.44 g at Lenihan Dam and 0.55–0.6 g at Austrian Dam, the dams developed some to extensive longitudinal cracks on the dam faces and settled at the dam crest on average 0.25 m at Lenihan Dam and 0.76 m at Austrian Dam. This study demonstrates the robustness of the adopted approach in capturing the embankment dam’s key performance under large earthquakes. The nonlinear response history analyses indicate that the proposed S_u/σ'_m approach for calculating in situ undrained shear strengths can be a reasonably conservative approach for engineering analysis and design. The calculated dam crest settlements for both dams are in good agreement with the dam crest settlements observed in the 1989 earthquake.