Modeling of laterally cyclic loaded monopile foundation by anisotropic undrained clay model

Abstract

Improved design methods for laterally loaded monopile foundation are crucial for the offshore wind turbine (OWT) sector, as established approaches no longer apply to such a pile foundation characterized by a relatively small length-to-diameter ratio. Numerical modeling is the primary approach to improve and validate design methods for monopiles and a central part of it is the soil constitutive model. This work presents a model that captures the essential mechanical characteristics of cyclically loaded undrained clay yet retains simplicity demanded by practicing engineers. This objective is realized by simplifying undrained clays as single-phase materials governed by total stresses and utilizing kinematic hardening plasticity. Via a new kinematic hardening rule, strength and stiffness anisotropy of clay and their cyclic deterioration are accommodated. The model is evaluated at different scales of simulating laboratory soil tests and analyzing monopile subjected to monotonic and repeated lateral loading in geotechnical centrifuge tests. The latter validation provides an encouraging demonstration of how monopile foundation can be numerically analyzed based on soil data acquired mainly from in situ site characterization and routine laboratory tests.