3D stability analysis of gravity dams: An introduction to spade-stroke mechanisms

Historical failures of rock foundations have highlighted the vital role foundation stability of concrete dams plays in the overall stability of the structure. Although stability analyses are carried out for both arch and gravity concrete dams, it has become common to perform 2D foundation stability analyses for gravity dams and 3D analysis is considered exclusive to arch dams. Many dam engineers use the bearing capacity formula or the 2D wedge methods for stability analysis of gravity hydraulic structures. In this paper the importance of realistic 3D stability analyses for gravity structures is discussed. A group of ‘spade-stroke wedge mechanisms’, which are common to gravity structures, are introduced and the computational aspects are briefly explained. Finally, an illustrative example of 3D stability analyses based on the spade-stroke mechanisms is presented and the sensitivity of the stability to various geometrical and loading aspects are evaluated.