Estimation of Linear Spring Constant for Laterally Loaded Monopile Embedded in Nonlinear Soil

Abstract

A single large diameter pile, known as monopile, is often provided to carry all the loads and moments being transferred from the superstructure. In such a case, accurate estimation of displacement and slope become imperative. 1D, 2D or 3D modelling can be done to simulate deflect tion of pile. For 1D simulation using Winkler’s model, the spring constant can be calculated from shear modulus of soil. There are many recommendations available in the literature to estimate maximum shear modulus of soil. The predicted maximum shear modulus from various recommendations indicates that the direct correlations with SPT value have relatively less uncertainty of prediction. 1D model predictions using existing simple correlations between spring constant and soil modulus generally overestimate the deflection of pile when compared to 3D model. Through a comparative study of results from 1D and 3D simulation, a new expression for estimation of spring constant from soil modulus is proposed which incorporates relative stiffness of soil and pile. It is also known that soil is nonlinear material and its stiffness reduces with increase of strain level, hence, it is important to know the amount of expected lateral strain in soil at different depths. A coefficient has been proposed to estimate the approximate value of equivalent lateral strain in soil by assuming strain as a function of top deflection and diameter of pile.