Evaluation of Seismic Settlement Potential of Saturated Sandy Ground Based On Concept of Relative Compression

ABSTRACT Mechanisms regarding the earthquake-induced settlements of saturated sandy deposits with level or nearly level ground surface are revealed based on new post-earthquake stress-strain constitutive analysis and experimental evidence. It was found that: 1) the residual volumetric strain of saturated sand evr induced by drained consolidation following cyclic undrained loading, depends on an irreversible dilatancy component evd.ir and a residual shear strain during the consolidation γr only; 2) change in evd.ir can universally be measured using an index “relative compression, Rc” for different sands over a wide range of density; and 3) a consistantly good correlation exists between Rc and maximum double amplitude shear strain induced by preceding cyclic undrained loading. From these theoretical and experimental findings, new analytical and empirical methods with a high degree of physical rationale were developed for predicting earthquake-induced maximum undrained shear strain and the resulting residual volumetric strains. As a consequence, the seismic ground surface settlement potential for level sandy deposits can be evaluated only by integrating the relative compression along ground depth. The proposed methods were confirmed to be effective by comparing the predictions with observations made during the 1995 Hyogoken-Nambu earthquake.