Winkler Spring Coefficients for Laterally Loaded Piles

Winkler spring methods are widely used in the analysis of piles, but the elastic Winkler spring coefficient is still a subject of research, especially for large-diameter monopiles. This study proposes a three-dimensional (3D) rigorous solution for piles covering the entire range of flexibility in different soil profiles. The simplified 1D Winkler-type model is then calibrated. It is shown that the elastic p-y spring coefficients depend mainly on the pile aspect ratio and the pile-soil modulus ratio, and not on the pile diameter. The pile with relative pile-soil stiffness greater than 0.05 is characterized as a rigid pile. The difference between flexible piles and rigid piles is mainly due to the reduction of the pile aspect ratio. The reasons for the underestimation of monopile stiffness are further analyzed. The flexible piles are unable to mobilize the soil stiffness along the lower part of the pile, while the base effect of rigid piles is significant due to stress concentration. The spring coefficients are averaged using the equivalent work method. Some of the existing solutions provide a good approximation for flexible piles, while for rigid monopiles, the dimensionless spring coefficients are mainly related to the pile aspect ratio and the soil Poisson's ratio.