At zones of strong impedance contrast in which there is a significant change in stiffness between adjacent geomaterial layers, Winkler-based analysis methods predict abrupt changes in the internal pile reaction force effects for laterally-loaded foundation elements. In particular, the sudden de-amplification of moment when transitioning from a soft to stiff layer is accompanied by amplification of pile shear. From a design perspective, this is problematic when considering large lateral loads and moments acting on drilled shafts, because it can result in bulky transverse reinforcement designs that pose constructability challenges. This paper will review the challenges associated with the lateral performance of piles in zones with strong stiffness contrasts and present a large-scale experimental research program that investigates the lateral load transfer of rock-socketed deep foundation elements. The study seeks to better understand the ability of numerical and analytical methodologies in capturing the behavior at impedance interfaces, compare such with experimental observations, and derive lessons for the construction industry in how to optimize the design requirement using performance-based predictions for deep foundations embedded in stiff materials.
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