Abstract: The stiffness of soils at small strain level is different from that at large strain level obtained by normal triaxial tests. Small-strain characteristics of soil play an important role in the analysis of deformation in deep excavations, tunnels and other underground engineering. A series of static triaxial tests equipped with Hall Effect local strain transducers and dynamic tests using resonant column with bender element are carried out to study the small-strain characteristics of typical Shanghai natural clays (i.e. Layer2~Layer6). The results of this study show that the shear modulus increases with the increase of depth of soil layer. Shear modulus of the over-consolidated Layer 6 decays more rapidly than that of the other normally consolidated layers (i.e. Layer 2~ Layer 5). The initial shear modulus and the normalized shear modulus degradation are obtained by the resonant column. Both the triaxial tests and the dynamic tests can reveal the non-linear decay trend of shear modulus with the increasing of shear strain.

Key words: Shanghai cohesive soils, small-strain characteristic, stiffness decay, initial shear modulus, non-linear