Abstract: The earthquake failure of core rockfill dams is a gradual process, but deterministic failure criteria were adopted in its previous seismic vulnerability studies, and the classification of its grades is ambiguous due to limited understanding of its mechanism and grades. This paper describes a seismic vulnerability analysis method for core rockfill dams, considering the fuzziness of failure criteria. First, the fuzzy set theory is used to fuzzily the threshold values of dam damage levels; and to quantify the seismic fuzzy damage levels, we formulate a fuzziness coefficient that reflects the membership function form and the size of the fuzzy interval. Then, a fuzzy-probability integral formula for calculating the seismic vulnerability function is derived from the fuzzy seismic damage level. For the calculation, this formula makes up for the deficiency of its existing formula that is based on the deterministic failure criterion. Combined with the probabilistic seismic demand model, this new formula gives a dam seismic vulnerability curve under the fuzzy failure criterion and predicts the probability of dam structure failure at different levels corresponding to different earthquake intensities. Our method is applied to the seismic vulnerability analysis of a core rockfill dam in Southwest China. Results show that the seismic fragility curve obtained using the fuzzy failure criterion follows a trend similar to the traditional curve. Under the fuzzy criterion, the subsidence rate of the dam crest increases the membership degree for high-level damage, resulting in an increase in the probability of high-grade dam body failure under the same earthquake intensity. And a greater ambiguity coefficient means a greater impact of the failure criterion ambiguity on seismic vulnerability.

Key words: core rockfill dam, seismic vulnerability, failure criterion, fuzzy uncertainty, fuzzy-probability integral