Abstract: he seismic design of high concrete face rockfill dam (CFRD) situated over thick layered alluvial deposit poses significant challenge. This research focuses on the seismic responses of both the deep alluvial deposit and the dam, using a plasticity constitutive model for large post-liquefaction deformation of sand (CycLiq) with solid-fluid coupled analysis on high-performance GEOSX platform. The findings reveal that seismic responses are notably stronger in areas adjacent to the banks, where the alluvial deposit is thinner. This underscores a limitation in the reinforcement effect of gravel columns at the center of the value with deep alluvial deposit. Moreover, the research proposed an optimized treatment scheme, emphasizing the reinforcement of the alluvial deposit near both banks with a large area replacement ratio of gravel columns, yielding significant improvement in seismic reinforcement effects with an 80% decrease of gravel column treatment, where joint deformation exhibits up to 26% reduction.