Abstract
A high-cycle accumulation (HCA) model predicting the accumulation of permanent strain or excess pore water pressure in clay under a large number of load cycles is presented. Data from an extensive laboratory testing program on kaolin under undrained cyclic loading has been analysed for that purpose. The influence of strain amplitude, void ratio, stress ratio, overconsolidation ratio and loading frequency on the accumulation rates is considered in the constitutive equations of the HCA model. The proposed model is validated first by the simulation of element tests. Subsequently, its application to offshore wind turbine foundations under long-term lateral cyclic loading is presented by the back-analysis of a centrifuge test on a monopile in soft clay. The results are in good accordance with the measurements in terms of pile displacement and bending moment versus number of applied cycles. It is concluded that the proposed model is feasible to describe the long-term behaviour of clay subjected to high-cyclic loading.
Highlights
Similar to sand, clay can show an accumulation of permanent strain due to cyclic loading with many repetitions
Its application to offshore wind turbine foundations under long-term lateral cyclic loading is presented by the back-analysis of a centrifuge test on a monopile in soft clay
Highcyclic loading is relevant for many structures, the most prominent and actual example being offshore wind turbine (OWT) foundations which are continuously loaded by wind and water waves during their lifetime
Summary
Clay can show an accumulation of permanent strain due to cyclic loading with many repetitions. To take into account these influencing factors and to allow for a reliable estimation of the permanent deformations of OWT foundations subjected to millions of load cycles, the application of numerical methods in combination with special constitutive models can represent a feasible approach. In order to account for millions of load cycles, as faced in the offshore environment, special constitutive models such as the so-called high-cycle accumulation (HCA) models can be applied. These models are formulated in general stress– strain rate form, but do not predict the soil response during individual cycles. To show the applicability and robustness of the proposed model and to extend its validation to a larger scale, a monopile foundation for OWTs under cyclic lateral loading is studied in the framework of a back-analysis of a centrifuge model test
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