On the correlation of “static” and “dynamic” stiffness moduli of non‐cohesive soils

The secant stiffness of the stress – strain – hysteresis during a cyclic or dynamic loading with very small strain amplitudes is sometimes called “dynamic” stiffness of a soil. In contrast, a “static” stiffness is obtained from the first loading curve in oedometric or triaxial tests. Indeed, the difference between “dynamic” (small‐strain) and “static” (large‐strain) stiffness moduli is due to the different magnitude of strain or strain amplitude and not due to different loading rates. The small strain stiffness is an important design parameter for foundations subjected to a cyclic or dynamic loading. However, its determination in situ or from laboratory tests is laborious and expensive. In practice, the small‐strain stiffness is often estimated by means of a diagram correlating “dynamic” and “static” stiffness moduli. However, the assumptions and the range of applicability of this correlation are not clear. The present paper presents an inspection of this correlation for four sands with different grain size distribution curves. The “static” stiffness was obtained from tests with monotonic oedometric or triaxial compression. The “dynamic” stiffness was determined in resonant column tests and from measurements of the P‐wave velocity. For some of the tested sands, significant deviations of the experimental data from the correlation actually used in practice were obtained. Modified correlations are proposed in the paper.