UCLA Civil and Environmental Engineering

An eccentric mass shaker mounted to the crest of a model levee resting on very soft peat soil was used to measure dynamic base shear-displacement and base moment-rotation relations. The model levee rotated and translated visibly during testing, exhibiting a response that deviates significantly from the one-dimensional wave propagation assumption often used to analyze the seismic response of levees. We evaluate complex-valued stiffness and damping of the levee-foundation soil interaction for translational and rotational modes of vibration. The damping is strongly dependent on frequency, indicating that it is controlled by radiation of energy away from the vibrating levee. These radiation damping effects are dominant even at low frequencies that are well within the range of engineering interest for ground failure evaluations. Interestingly, the levels of radiation damping are roughly comparable, when expressed as percentage of critical, to predictions from classical models for impedance functions of rigid rectangular foundations on an elastic half-space. More research is needed to generalize these observations for application to seismic analysis of levees resting on peat.