Averted Piping Failure—Earth Dam on Permeable Foundation

“The dam builder has substantial control over the properties of the structure he builds, but he must take the foundation as it is furnished by nature.” (Cedergren, 1989) This paper presents the case of an earth dam built on a permeable foundation where seepage problems nearly caused failure of the dam. Early during first filling, before the lake was even half full, the dam showed significant seepage. Seepage boils appeared at the dam’s toe, indicating the onset of piping failure through the foundation. Although seepage boils indicating a failure mechanism appeared, dam failure was averted. The paper describes the events leading to the dam’s first filling incident, the averting of failure, and engineering for renovation. Construction of dams on permeable soils is relatively common (often unavoidable). The typical dam site has some alluvial soil in vicinity of the water course, soils that are usually permeable. Potential for seepage-related problems generally depends on the engineer recognizing a permeable foundation and designing the dam accordingly. The dam’s behavior—good or bad—depends on the measures taken to accommodate seepage, such as a foundation seepage cutoff and filter-drain protection. Higher permeability generally means higher potential for problems at the downstream toe. This paper presents several interesting aspects of a case history supporting/illustrating this contention: ● Original design and construction ● Problems and near-failure conditions encountered at first filling ● Comparison of the dam to others with permeable foundations and evaluation of other dams where design did and did not accommodate permeable foundation conditions ● Engineering approach to renovation ● Performance in servic