Size Effects of Ground Improvement on Seismic Response of Piles: Derivation and Validation of p-y Curves

We use the results of pseudo-static and seismic load tests on centrifuge model piles to investigate the effects of improved zone size on the soil-pile interaction mechanisms in cement-improved soft ground. In deriving the p-y curves that are typically used for modeling the soil-pile interaction, we implemented a modified bending moment curve-fitting procedure that accounts for discontinuities inherent in the distribution of soil reaction at the interface of the improved and unimproved soils. Our experimentally derived p-y curves show the influence of the improved layer on the behavior of the underlying soft clay layer and vice versa. The standard p-y curves performed reasonably well for estimating the stiffness of the largest improved zone but over-predicted the stiffness of the smallest improved zone. The standard p-y curves also showed good agreement with the backbones of the seismic p-y curves in the soft clay away from the improved zones. We evaluated the reliability of a simplified pseudo-static analysis for a seismic excitation and obtained satisfactory results for the largest improved zone. Our analyses reveal the dominant nature of kinematic interactions in the response of the improved piles.