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

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 Gdyn=Gmax and the small-strain constrained modulus Mdyn=Mmax 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 Mstat=Moedo, while the large-strain Young's modulus Estat=E50 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=qmax/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 Mmax and Moedo proposed in the literature underestimates the dynamic stiffness of coarse and well-graded granular materials. Consequently, modified correlation diagrams for the relationship Mmax↔Moedo are proposed in the present paper. Furthermore, correlations between Gmax and Moedo or E50, 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.