Development of a Scale Model for the Dynamic Interaction of a Pile in Clay

Abstract

Similitude theory is used to develop a scale model for determining the dynamic response properties of a single pile embedded in over-consolidated clay. The basis for the design is a full-scale pile embedded in natural soil, for which dynamic response measurements had been made in previous work. Correlation of the model and prototype results constitutes a major difference in this work over previous efforts using scale models. 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 monotonic stress and cyclic stress soil tests. Nonlinearity of the soil stiffness is included in the modeling. Dynamic response of the pile is monitored while excited by impact and swept sine forces at the pile top cap. The results are obtained in terms of time histories for excitation and response at various locations, frequency response functions, natural frequency and mode shapes, and modal damping. Validity of the model is established by comparing the appropriately scaled responses with those of the prototype under similar excitation conditions. It is concluded that the approach should be suitable for measurement of pile/soil dynamic interaction behavior in other types of material and excitation conditions, providing that suitable soil and pile material properties can be selected to allow testing in a one-g environment. Therefore, the scale model approach can be used to verify predictions made by analytical design methods or to provide input parameters for those methods.