Dynamic pile impedances for laterally-loaded piles using improved Tajimi and Winkler formulations

Lateral dynamic soil-pile interaction is investigated through an improved Tajimi type solution. The soil is treated as a continuum with hysteretic material damping as previously proposed by the authors, and the pile is modelled as beam using traditional strength-of-materials solutions. Following the pioneering work of Novak and Nogami, a more accurate analytical model for the static and harmonic response of a pile in a soil layer overlying rock is proposed, and closed form expressions for pile head stiffness are derived. Results are validated through comparisons against rigorous solutions from literature. Hereafter, the Winkler model was considered as a simple alternative for predicting pile head stiffness and damping. An extensive review of available Winkler moduli demonstrated that the Winkler model performance strongly depends on the selection of the respective moduli but found to be satisfactory in static conditions. Most existing expressions for dynamic Winkler moduli were found to render the model incapable of capturing resonant effects. Consequently, a new expression for a dynamic Winkler modulus is derived based on a modification of the classic dynamic plane strain modulus of Baranov-Novak. Implemented in the Winkler model this expression is capable of accurately computing dynamic stiffness attenuation and damping increase for frequencies up to the first resonance over a wide range of pile slenderness ratios.