Estimation of the linear spring constant for a laterally loaded monopile embedded in nonlinear soil

In the case of large-diameter monopiles, pile deflection against lateral loads must be predicted accurately to determine the direct influence on the superstructure. One-dimensional (1D) linear models of the pile-soil system, which are simple to analyze, are more commonly used in practice than the sophisticated three-dimensional (3D) simulations. This study proposes an equivalent lateral strain concept to incorporate soil nonlinearity into an equivalent linear analysis of the pile-soil system. The spring constant is obtained by iterating over soil stiffness at different strain levels and finding equivalent lateral strain from updated pile deflection at each iteration. It requires the maximum shear modulus and modulus reduction curve for different layers of the soil profile. Correlation between the equivalent lateral strain and pile deflection has been developed by comparing results from 1D and 3D simulations of long piles. The existing correlations between the lateral spring constant and Young's modulus of soil are too approximate to help in quantifying nonlinearity of soil accurately in this comparative study. Therefore, a more accurate relationship between spring constant and Young's modulus of soil for long piles has been proposed by incorporating relative stiffness of soil and pile.