Reservoir Bottom Absorption Effects in Earthquake Response of Concrete Gravity Dams

Utilizing a recently developed analytical procedure, linear responses of the tallest non‐overflow monolith of Pine Flat Dam to Taft ground motion are presented for a range of properties for the reservoir bottom materials and various assumptions for the impounded water and foundation rock. In these analyses, the alluvium and sediments at the reservoir bottom, up‐stream of the dam, are modeled by a reservoir bottom that partially absorbs incident hydrodynamic pressure waves. Based on these response results, it is demonstrated that the earthquake response of dams is increased by dam‐water interaction and decreased by reservoir bottom absorption with the magnitude of these effects depending on the flexibility of the foundation rock and on the component of ground motion. It is also shown that the significance of the response of dams to vertical ground motion was overestimated in earlier studies assuming a rigid reservoir bottom.