Scale Model Study of Pile Foundations Under Earthquake Excitation

Similitude theory is used to develop scale models for determining the earthquake response of pile foundations embedded in overconsolidated clay. The model is compared with full-scale foundations embedded in natural soil, for which dynamic response measurements had been made in previous work. Correlation of the model and prototype earthquake response constitutes a major difference in this work over previous efforts using scale models. Gravity effects are included in the models by scaling pile and soil material properties. The model pile material is selected to provide the correctly scaled stiffness and mass properties. The required model soil properties are achieved by developing a mixture of bentonite, aerosil, and veegum. Elastic properties of the model soil are compared with those of the prototype by standard momotonic stress and cyclic stress soil tests. It is found that scaling considerations must also apply to supporting static soil tests for determining soil properties, as well as to the model piles for measurement of dynamic responses. Soil property nonlinearities are shown to be distorted by geometric effects. However, a method is developed to account for the distortion as long as excitation waveforms are similar. The successful correlation of pile data extends the relationship between frequency parameter and relative soil strain to much higher strain levels than those obtained in the prototype tests. Therefore, the potential for a significant savings in future investigative work is demonstrated with scale model testing.