A unified-plot approach for the assessment of internal erosion in embankment dams

Surpassed only by overtopping as the larger contributor to the failure of embankment dams, internal erosion occurs when fine-grained particles are allowed to erode by the action of seepage. A dam may be susceptible to internal erosion if there are erodible surfaces not protected by filters. Signs of internal erosion of dams may be sinkhole formations, increased seepage, and muddy discharge. Most methods to assess potential susceptibility are empirically based with little or no comparison to field experience. Based on a database of 80 embankment dams that includes 23 dams reported to have experienced some form of internal erosion and exhibited signs of internal erosion, analysis indicates a correlation between dams with internal erosion and characteristics of the filter of a dam. From comparison with field experience, an approach to assessing existing dams and internal erosion is proposed in this paper by combining attributes of filter gradation in a unified plot, namely its internal stability and its capacity for soil retention. The unified plot may serve as a preliminary screening tool for the susceptibility of internal erosion of dams.