Assessment of the filter criteria in an experimental embankment dam

Sammanfattning

Internal erosion is one of the most common leading causes of embankment dam failures, often linked to poor filter design and construction practices. This thesis investigates the performance of fine filters in the Vattenfall experimental dam, built at their facilities in Älvkarleby in 2019 and demolished in 2024, focusing on their adherence to Swedish safety guidelines RIDAS 2012 and RIDAS 2019. Soil particle distribution analyses of the core and fine filter materials showed deviations from the original design: the as-built fine filters were coarser, while the core materials were finer than specified. These differences reduced the filters’ capacity to retain soil particles, increased the dam’s vulnerability to seepage, and further compromised internal stability. Observations during demolition confirmed these issues, revealing internal erosion channels, piping, and material migration at various dam levels.This study “bridges” the gap between guideline-based design and actual dam performance by combining laboratory analyses, construction records, and demolition observations. Although the RIDAS 2019 guidelines introduced stricter criteria than RIDAS 2012, they did not prove more effective at predicting where defects would develop. Erosion was often observed even in levels meeting the guideline requirements, highlighting limitations of design criteria when not supported by proper construction quality control. This work provides valuable empirical insights into how filter deficiencies emerge and develop over a dam’s life cycle.Finally, the findings deepen the understanding of internal erosion mechanisms, underscore the importance of experimental dams as research platforms, and offer practical suggestions for improving dam safety. These insights aim to support future updates to dam safety guidelines, as well as the operation, maintenance, and rehabilitation of existing embankment dams, helping to strengthen their resilience and reduce societal risks related to dam failures.