STATE OF THE ART IN MODELLING OF SOIL BEHAVIOUR AT SMALL STRAINS

The present paper is an attempt at a comprehensive overview of studies on behaviour of overconsolidated soils at small strains. The text has been divided into six sections related to different aspects of the addressed issues. The first section provides an introduction. The subject of the second section is the phenomenon of abrupt drop of the tangent shear and bulk moduli when increasing corresponding strain invariants in the ranges of their small values. Special attention is paid to evaluating the maximum values of moduli which are constant in a region of very small strains. The third section concerns the nature of the above mentioned material properties. The results of the discussed Jardine's experiments indicate that there exist four regions of different soil behaviour around a stable stress point within the admissible state space. The fourth section focuses on simple hypoelastic laws for soils describing steep decreasing tangent shear and bulk moduli at small to moderate strains. The fifth section presents advanced kinematic hardening elasto-plasticmodels which take into account, in different ways, strong stress-strain nonlinearity at small deformations. Two models are described in more detail. The first of them is the one surface model of the cryptonym NAHOS 1 and the other is the three surface SH3 one. The conclusion inserted in the latter sixth section discusses briefly beneficial outcomes of accounting for small strain nonlinearity phenomenon.