Optimal ground motion intensity measures for the seismic vulnerability assessment of embankment dams

The seismic response of embankment dams is critical for effective seismic design, yet probabilistic seismic demand models (PSDMs) for these structures remain underexplored. This study develops PSDMs to identify the optimal Intensity Measure (IM) for embankment dams by evaluating 14 different IMs. Two approaches are employed for PSDM development: one utilises empirical data from earthquake records from instrumented embankment dams, while the other is based on numerical simulations using a Finite Element Method model of dam subjected to ground motion records from free-field and dam site stations. A novel fuzzy comprehensive IM evaluation framework is proposed, and using this framework, it was found that Root Mean Square Velocity (VRMS) from empirical PSDM and Peak Ground Velocity (PGV) from the numerical analysis PSDM are the most optimal IMs. In contrast, Effective Design Acceleration is least optimal IM across both approaches. The study then classifies dam damage into five states using relative crest settlement ratio as the engineering demand parameter. Seismic fragility analysis conducted through both PSDM approaches indicates that Peak Ground Acceleration, a commonly used IM, significantly underestimates the probability of damage to embankment dams, with maximum underestimations of 44% and 30% observed using the empirical and numerical PSDMs, respectively.