The seismic design of earthfill and rockfill dams routinely relies on methods of analysis, which adopt simplifying assumptions regardingthe damgeometry, soil behaviour and the dynamic interaction of the fluid and solid phases within the dam body. This paper explores such simplifying assumptions, which aretypically used for thenumerical modelling of earthfill and rockfill embankment dams,within the context of two case studies. First a clay core dam,theLa Villita dam in Mexico, is considered focusing mainly on the implications of 2D plane strain approximation in the case of dams built in relatively narrow canyons. In the second case study, of the rockfill Yele dam in China, the importance of hydro-mechanicalcoupling is explored by parametrically varying the permeability of the materials.