Damping at Small Strains in Cyclic Simple Shear Test

Mladen Vucetic, & Macan Doroudian

Published July 1998, SCEC Contribution #397

Cyclic tests were conducted to study damping properties of two reconstituted sands and three laboratory-made clays at small cyclic shear strain amplitudes of gammac[approximate] 0.001–0.04%, employing a recently developed constant-volume equivalent-undrained direct simple shear device for small-strain testing. The tests were strain-controlled with an approximately sinusoidal shape of cyclic straining. The effects of cyclic strain amplitude (gammac), frequency of cyclic loading (f), plasticity index (PI), silt content, vertical effective consolidation stress (sigma^[prime]_vc) and overconsolidation ratio (OCR) on the equivalent viscous damping ratio, lambda, were investigated. The results show that, for a given gammac, lambda decreases with sigma^[prime]_vc and OCR, but both of these effects become smaller if PI increases. The effect of f on lambda was not observed for f[approximate] 0.01–0.1 Hz. The results also show that below gammac[approximate] 0.005%, lambda for clays is larger than lambda for sands, which is exactly the opposite of the trend above gammac[approximate] 0.005% established previously. Such a reversal of the trend of lambda with respect to the type of soil is explained by the relative contributions of soil nonlinearity and soil viscosity to the area of the hysteretic cyclic stress-strain loop at small versus large cyclic strains.

Citation
Vucetic, M., & Doroudian, M. (1998). Damping at Small Strains in Cyclic Simple Shear Test. ASCE Journal of Geotechnical and Geoenvironmental Engineering, 124(7), 585-593. doi: 10.1061/(ASCE)1090-0241(1998)124:7(585).