The Effects of Preloading History on the Undrained Behaviour of Saturated Loose Sand

Abstract

ABSTRACT This paper presents a comprehensive analysis of the effects induced by drained and undrained preshear and, in general, by preloading history on the undrained behaviour of loose sand prepared by moist tamping. The results are interpreted from the point of view of understanding the evolution of elastic anisotropy and the shape of the yield surface. The undrained behaviour of loose sand is shown to be a powerful and expeditious means for analysing the effects of stress-induced anisotropy. At first the reliability of this approach is evaluated through a comparison of the undrained effective stress paths with the stress states corresponding to a stiffness change along drained stress paths of samples subjected to the same preloading history. Subsequently the effects induced by isotropic preconsolidation, by drained preshear at different maximum stress ratios and along different stress paths, by undrained preshear and, finally, by drained cyclic preshear are analysed in detail on samples with similar void ratios at the beginning of the undrained loading phase; the results are discussed in terms of the evolution of the yield surface and elastic anisotropy. This paper is consequently both a further development in the analysis of the effects of preloading history on the undrained behaviour of saturated loose sand and another step towards a better understanding of the mechanisms governing the evolution of mechanical anisotropy in loose sands along triaxial stress paths.