Characterization of the dynamic behavior of shallow foundations with full-scale dynamic tests

This work provides a detailed description of the full-scale experimental tests performed on the dynamic behavior of a shallow foundation under intermediate strains. A wind tower supported by the foundation was subjected to a snap-off test, i.e., it was first pulled with a cable and then suddenly released, thus inducing free oscillations of nonnegligible amplitude in the whole system. The motion induced was measured with a digital camera, seismometers, and accelerometers attached to the surrounding ground surface and to the wind tower. An innovative interpretation technique based on optimizing a few meaningful parameters obtained from the recorded time histories was required by the heterogeneity of the data collected and the accuracy needed to deduce the behavior of the foundation plinth. The analyses showed that the rotational stiffness of the foundation plinth was approximately 10 times greater than that of the base joint, which in turn was approximately one order of magnitude greater than that of the wind tower. As a result, the vibration phenomenon was driven by the wind tower, which induced a sort of forced, damped, harmonic excitation in the foundation such that the tower’s oscillations and the foundation’s rocking were decoupled from one another. Seismometer measurements performed on the ground surrounding the foundation plinth enabled an assessment of the geometrical attenuation of the surface vibrations induced by foundation rocking. To the best of the authors’ knowledge, the geometrical attenuation assessments reported in this study are the first to be published on the deformations of the ground surrounding a rocking foundation, and could serve as a useful reference to validate constitutive models for simulating small-strain soil response. © 2016 American Society of Civil Engineers