On the Erasing of the Cyclic Preloading by Monotonic Deformations in Granular Soils

Abstract

For the design and construction of Offshore Wind Energy Turbines (OWT), it is essential to predict deformations in the subsoil. Wind and waves cause a high-cycle loading on these structures. To ensure their servicability, reliable soil models for predicitions of cumulative displacement over the expected OWT lifetime are needed. In this work, the explicit constitutive High-Cycle Accumulation Model (HCA-Model) by Niemunis et al. [1] has been modified to account for the influence of large monotonic strains on the rate of subsequent cyclic accumulation. In this research project, 21 drained cyclic triaxial tests on saturated, cylindrical Karlsruhe fine sand samples were performed. The packages of cycles were applied on the specimens one after another. Between the packages, the average stress state was monotonically changed. To examine the reduction of the so called cyclic preloading, the tests were analysed regarding the accumulated strain throughout the packages of cycles in each test and the monotonic strain resulting from the change of the average stress state between the packages. In addition, finite-element calculations on an exemplary shallow foundation of an OWT were performed. Two packages of cycles with modification of the cyclic preloading were studied. The reduction of the cyclic preloading was evident.