AbstractThe upstream or waterside slopes of water-retaining structures, such as earth dams and levees, must be designed for rapid drawdown (RDD). While multiple instances of RDD failure have occurred, only two case histories, Pilarcitos Dam and Walter Bouldin Dam, have sufficient shear strength data to be useful for validation of analysis procedures. This paper documents a RDD failure at Sparmos Dam in Northern Greece in 2016, including the results of index, compaction, and triaxial compression tests on soil from the dam. Based on the collected data, the factor of safety following RDD is calculated using two effective stress and two undrained methods. The B¯ effective stress method and both undrained methods are able to predict the Sparmos Dam failure, if a conservative interpretation of shear strength is employed. In contrast, the effective stress evaluation of RDD using uncoupled transient seepage analysis produces invalid results when appropriate values of the coefficient of consolidation are used. The Sparmos Dam case history highlights the need for ongoing study of RDD analysis procedures and shows that pore pressures from uncoupled transient seepage are unreliable for RDD.

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