Rate-Dependence of Rockfill Behavior on Propagated Near Fault Ground Motions

Equivalent linear one-dimensional site response analysis, which approximates the nonlinear soil behavior within the linear analysis framework, is widely used in estimating local site effects. In this analysis, soil behavior is often assumed to be independent of the frequency of seismic loading. However, the large scale triaxial test results on rockfill material have shown that the shear modulus, and especially the damping ratio, are influenced by the loading frequency. A series of one-dimensional equivalent linear analyses were performed on 30m and 90m thick profiles of the studied rockfill material to evaluate the frequency-dependent soil behavior under several well-known near-fault ground motions. The analyses are carried out for three base acceleration levels, namely, 0.1 g, 0.35 g, and 1 g, using the simple time history scaling method. Results show that the frequency-dependent shear modulus and damping ratio can have a pronounced influence on propagated ground motions. The frequency-dependent soil behavior is also dependent on the thickness of soil profile,amplitude, equivalent no. of cycles at 0.65τmax, and frequency content of the input ground motion.