Pre-failure deformation characteristics of geomaterials

Most of the papers submitted to session la on "Laboratory tests" deal with clayey and sandy soils while only a limited number of studies are devoted to the stiffness characteristics of gravels and rocks. Among cohesive soils, reconstituted clays still predominate indicating the need for further laboratory investigations of the small-strain behaviour of natural clays. The main topics selected for discussion in the next sections concern the different results obtained using different testing techniques and possible reasons for this; the importance of accounting for soil state when studying the small-strain shear stiffness and some of the options available to reduce experimental data; the evaluation of soil microstructure and sample disturbance; the stiffness anisotropy at small strains under axi-symmetric or general stress conditions.