The influence of installation effects on the bearing characteristics of piles under lateral cyclic loading in sand

The displacement pile installation process significantly affects the stress and strain fields in the surrounding soils, which is often neglected for simplicity in conventional analysis and design. It is crucial to investigate the pile installation effects on the bearing characteristics of offshore wind turbine piles subjected to lateral cyclic loading. In this paper, a state dependent Mohr-Coulomb constitutive model is introduced first to describe the dilatancy and cyclic degradation of sand. The model is then incorporated into the Eulerian-Lagrangian method (CEL) of a three-dimensional finite element to simulate the pile penetration process and obtain the stress field developed in the sand mass during the installation. Two simulation scenarios are considered in the numerical model: one with in-situ stress field (pile introduced as wished-in-place) and the other with the stress field resulting from the pile installation. Lateral cyclic loaded pile tests are conducted on the model, considering varying pile shaft elastic moduli, lateral cyclic load cycles, and amplitudes. A comparative analysis is performed to evaluate the bearing characteristics of cyclic loaded piles and the response of the surrounding soil in both cases. The results show that, for a given number of cycles and amplitudes, the installation effect reduces the cumulative displacements at the pile head under lateral cyclic loading, while increasing the lateral bearing capacity of the pile. The findings of this study provide valuable guidance for offshore pile design, particularly in considering installation effects, material selection and load analysis.