Advantages of converting old homogeneous earth dams into upstream-faced dam typologies

Homogeneous earth dams are well known to perform poorly under high-intensity seismic loading, a limitation widely recognized in the literature. This paper investigates whether a fine-grained dam, retrofitted solely with an upstream waterproofing system, can meet current seismic standards under strong ground motion. To address this question, a well-documented case study of an earth dam originally built as a homogeneous embankment is examined. The reference dam experienced global instability, likely due to additional crest load and a nearby seismic event. After the failure, part of the original embankment was retained, and a new upstream-faced dam was constructed atop it using coarser materials. The study evaluates whether a moderate nearby earthquake could have contributed to the failure of the original homogeneous dam and explores the feasibility of upgrading existing homogeneous dams to upstream-faced solutions without any other modification of the embankment. Numerical analyses show that the combined design of an extended upstream liner (along the horizontal upstream surface) and an impermeable diaphragm wall embedded in the foundation soil can effectively withstand expected seismic loading, offering a cost-effective and less disruptive rehabilitation strategy compared to full dam reconstruction, with moderate interventions and short operational downtime. However, the success of this design is highly sensitive to the permeability contrast between foundation and embankment soils, highlighting the critical need for accurate characterization of the saturated soil permeability.