This paper discusses the combined effect of foundation-reservoir interaction on the seismic response of concrete gravity dam by considering a case study: Bichom Concrete Gravity Dam located in Arunachal Pradesh, India. The dam comprises of overflow and non-overflow monoliths and seismic analysis was carried out for both monoliths separately for Design Basis Earthquake excitation (DBE) assuming linear behaviour. The significance of foundation flexibility on the seismic response of dam was investigated by comparing the response of dam with rigid and flexible foundations. The hydrodynamic effect of impounded water is modeled as an added mass by Chopra’s Method. Effect of foundation-reservoir interaction on the response of both monoliths, such as time period, crest displacement, base reactions and stress distributions are discussed in this paper. It is predicted from the analysis that the dam with rigid foundation is relatively safe except some minor cracks at the heel of non-overflow monolith, but the dam with flexible foundation suffers moderate damage when the reservoir is empty and full
