Dynamic soil pressures on deeply embedded structures
Younan, Adel Helmy
Veletsos, Anestis S.
Doctor of Philosophy
The studies reported herein are motivated by the need to gain improved understanding of the response to earthquakes of deeply embedded and underground cylindrical tanks storing nuclear wastes, and develop rational but simple methods of analysis and design for such systems. The first part of the study, reported in Chapters 2 and 3, is concerned with the dynamic modeling and response of soil-wall systems. Simple approximate expressions for the dynamic pressures and associated forces induced by ground shaking on a rigid, straight, vertical wall retaining a semi-infinite, uniform viscoelastic layer are developed, and comprehensive numerical data are presented which elucidate the effects of the numerous parameters involved. These solutions are then compared with those obtained by use of a popular approximate model, and the accuracy of the model is assessed. It is shown that the model may lead to substantial inaccuracies. The sources of the errors are identified, and a modification is presented that defines correctly the action of the system. The modified model is then used to evaluate the response of more involved soil-wall systems. The second part, comprised of Chapters 4 and 5, deals with the response to horizontal shaking of an upright, circular, rigid vault that is embedded in a uniform viscoelastic stratum of constant thickness and infinite extent in the horizontal plane. Both the vault and the stratum are presumed to be supported on a non-deformable base. Simple approximate expressions for the dynamic pressures and associated forces induced in the vault are developed, and comprehensive numerical solutions are presented. Furthermore, the accuracy of a popular model in which the medium is represented by a series of independent thin layers is investigated. The errors arising from such an idealization are identified, and a modification is proposed that describes correctly the behavior of the stratum. The last part, reported in Chapter 6, deals with the response to a lateral base shaking of a rigid cylinder containing a viscoelastic solid. Simple approximate expressions for the resulting dynamic wall pressures and tank forces are developed, and comprehensive numerical solutions are presented which elucidate the effects of the numerous parameters involved.