Multi-Modal Synthesis and Variable Modulus Effects in Resonant Column Tests by Random Excitations

To extend current measurement and data synthesis techniques for resonant column testing, random vibration transfer functions measured using a modified 6 inch (152.4 mm) diameter Drnevich free-free resonant column device are evaluated against viscoelastic theories of homogeneous and heterogeneous soil models. By means of the transfer function approach, it is found that the first four resonant peaks of the soil column response can be captured experimentally with some instrumental adaptations. By calibration against theoretical transfer functions, the ability to characterize the modulus and damping properties of the soil samples over a broad range of frequencies is demonstrated. As a generalization of the analytical theory for resonant column tests to a number of practical applications, the sensitivity of the experimental procedure to the specimen’s vertical material heterogeneity is examined for a linear variation in shear modulus. The feasibility of applying the experimental and analytical techniques to investigations of the frequency-dependence of damping properties is demonstrated. Calibration of theoretical models against measured resonant column soil behavior over a wide range of frequencies is anticipated to lead to more accurate material characterization across the spectrum of frequencies encountered in seismic and foundation vibration applications