Internal Erosion in a Full-Scale Experimental Embankment Dam: Insights from the Dismantling of the Älvkarleby Test Dam

Abstract

Internal erosion is a leading cause of embankment dam failure, yet its mechanisms remain difficult to observe directly. This study presents findings from the dismantling of a 4 m high, full-scale experimental embankment dam constructed in Älvkarleby, Sweden, with embedded defects. The dam featured a moraine core, protected by fine and coarse filters and supported by rockfill. After 4.5 years of operation, the dam was dismantled, revealing multiple internal erosion features despite adherence to modern design standards.

Key observations include a sinkhole-like feature with a softened, saturated zone underneath it, coinciding with one of four horizontally installed strain cables. Three horizontal erosion pipes were identified underneath a vertical coarse-column defect, aligned along horizontal core layer interfaces. A sandy zone near a wooden block defect and thin, sand-filled streaks at core layer boundaries were also documented, suggesting early-stage erosion along construction-induced stratification planes. Along the right abutment, a contiguous zone of disturbed core material and multiple small sinkholes were observed adjacent to the concrete wall.

Sieve analyses revealed both enrichment and depletion of fines in the downstream fine filter, highlighting variability in retention performance. Coarse filter segregation and core–fine filter incompatibility was suspected to contribute to a two-stage erosion mechanism. These findings underscore the critical role of construction-induced heterogeneities, moisture variability, and filter placement in internal erosion development. The study emphasizes the need for improved construction control, real-time monitoring, and post-construction verification to improve long-term embankment dam performance.