Seismic behaviour of earth dams - permanent displacement prediction

Abstract

ln   the  past  decade,  in  opposition   to  the  conventional   pseudo-static  approach,  designers of  large  earth  dams  devoted  much  effort  to  a  quantitative  assessment  of   the  structural   behaviour, based on permanent seismic induced displacement criteria. Whilst simple semi-empirical procedures may be attractive, the engineer is morally bound to use the best available methodologies to ensure that the structure, as conceived, is safe and economical. Therefore a comprehensive review of the usefulness and limitations of the principal available procedures is given.

It is shown that induced time-histories at the base of critical potential sliding mass must be properly determined for a rational evaluation of the permanent displacement. An example of application to an earth dam is given.

Induced strains in dynamic triaxial testing are insufficient to define post-peak strength and because significant displacements, along yield surfaces in earth dams, mobilize progressive failure, a method is proposed taking into account the dynamic brittleness of soils and the excess pore pressures generated during an earthquake. Ring shear and/or shacking table tests are then recommended.