Large-diameter monopiles are widely used foundations for offshore wind turbines. In the present study, three-dimensional finite element (FE) analyses are performed to estimate the static lateral load-carrying capacity of monopiles in dense sand subjected to eccentric loading. A modified Mohr-Coulomb (MMC) model that considers the pre-peak hardening, post-peak softening and the effects of mean effective stress and relative density on stress-strain behavior of dense sand is adopted in the FE analysis. FE analyses are also performed with the Mohr-Coulomb (MC) model. The load-displacement behavior observed in model tests can be simulated better with the MMC model than the MC model. Based on a parametric study for different length-to-diameter ratio of the pile, a load-moment capacity interaction diagram is developed for different degrees of rotation. A simplified model, based on the concept of lateral pressure distribution on the pile, is also proposed for estimation of its capacity.

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Different particle properties, such as shape, size, surface roughness, and constituent material stiffness, affect the mechanical behavior of coarse-grained soils. Systematic investigation of the individual effects of these properties requires careful control over other properties, which is a pervasive challenge in investigations with natural soils. The rapid advance of 3D printing technology provides the ability to produce analog particles with independent control over particle size and shape. This study examines the triaxial compression behavior of specimens of 3D printed sand particles and compares it to that of natural sand specimens. Drained and undrained isotropically-consolidated triaxial compression tests were performed on specimens composed of angular and rounded 3D printed and natural sands. The test results indicate that the 3D printed sands exhibit stress-dilatancy behavior that follows well-established flow rules, the angular 3D printed sand mobilizes greater critical state friction angle than that of rounded 3D printed sand, and analogous drained and undrained stress paths can be followed by 3D printed and natural sands with similar initial void ratios if the cell pressure is scaled. The results suggest that some of the fundamental behaviors of soils can be captured with 3D printed soils, and that the interpretation of their mechanical response can be captured with the critical state soil mechanics framework. However, important differences in response arise from the 3D printing process and the smaller stiffness of the printed polymeric material. Graphic abstract Artificial sand analogs were 3D printed from X-ray CT scans of sub-rounded and sub-angular natural sands. Triaxial compression tests were performed to characterize the strength and dilatancy behavior as well as critical staste parameters of the 3D printed sands and to compare it to that exhibited by the natural sands.

With increasing demand of energy, attention to the alternative sources of sustainable energy is getting priority over the last decades. Offshore wind turbine is one of them. The most widely used foundation system for the wind turbine is the monopile, which is a large diameter single pile. In the present study, three-dimensional finite element (FE) analyses are performed to evaluate the capacity of large diameter monopiles in dense sand using the Arbitrary Lagrangian-Eulerian (ALE) approach available in Abaqus/Explicit FE software. The behavior of sand is modeled using the Mohr-Coulomb (MC) and a modified Mohr-Coulomb (MMC) model where the pre-peak hardening, post-peak softening and the effects of mean effective stress and relative density on stress-strain behavior of dense sand are considered. Comparison with physical model test results shows that the MMC model can simulate better the load-displacement response than that with the MC model. The mechanisms involved in soil deformation are also explained using FE results.

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