On correlations between 'dynamic' (small-strain) and 'static' (large-strain) stiffness moduli - An experimental investigation on 19 sands and gravels

摘要

Correlations between "dynamic" (small-strain) and "static" (large-strain) stiffness moduli for sand are examined. Such correlations are often used for a simplified estimation of the dynamic stiffness based on static test data. The small-strain shear modulus G(dyn) = G(max) and the small-strain constrained modulus M-dyn = M-max have been measured in resonant column (RC) tests with additional P-wave measurements. Oedometric compression tests were performed in order to determine the large-strain constrained modulus M-stat = M-oedo, while the large-strain Young's modulus E-stat = E-50 was obtained from the initial stage of the stress-strain-curves measured in drained monotonic triaxial tests, evaluated as a secant stiffness between deviatoric stress q=0 and q = q(max)/2. Experimental data for 19 sands or gravels with specially mixed grain size distribution curves, having different non-plastic fines contents, mean grain sizes and uniformity coefficients, were analyzed. Based on the present data, it is demonstrated that a correlation between M-max and M-oedo proposed in the literature underestimates the dynamic stiffness of coarse and well-graded granular materials. Consequently, modified correlation diagrams for the relationship M-max M-oedo are proposed in the present paper. Furthermore, correlations between G(max) and M-oedo or E-50, respectively, have been also investigated. They enable a direct estimation of dynamic shear modulus based on static test data. In contrast to the correlation diagram currently in use, the range of applicability of the new correlations proposed in this paper is clearly defined.