Federico Pisanò

This paper presents a soil reaction framework for monotonic lateral analysis of offshore wind monopiles in sand, formulated using input parameters that can be derived from seismic cone penetration test (SCPT) data. The model adopts a multicomponent Winkler representation incorporating distributed lateral, distributed moment, and base shear reactions within a unified bounding-surface plasticity formulation. This approach enables direct linkage between soil reaction behavior and site-specific soil properties, namely small-strain stiffness and cone penetration resistance inferred from in situ measurements. Model calibration is supported by an original centrifuge testing program conducted within the Monopile Improved Design through Advanced Cyclic Soil Modeling (MIDAS) project, covering monopile geometries and sand densities representative of offshore wind applications. The calibrated parameter ranges are subsequently evaluated against independent field test data sets from the Pile Soil Analysis (PISA) and VIBRO research programs. Comparisons indicated that the proposed formulation reproduces global load-displacement response and bending moment distributions with satisfactory accuracy across a range of pile–soil relative stiffness conditions. The proposed framework provides a computationally efficient alternative to three-dimensional finite-element analyses for monopile design, particularly during early wind farm development stages when high-fidelity simulations are constrained by time and/or limited soil data.

The occurrence of flotation phenomena during trench backfilling remains a well-recognized threat to the successful installation of offshore pipelines, with direct implications for both safety and cost. This study developed and assessed a simplified model based on Kynch’s batch sedimentation theory to predict the buoyant response of pipelines during sand–water backfilling. The formulation couples the temporal evolution of solid concentration with the dynamic equilibrium of the pipe, accounting for both buoyancy and Bingham-type drag forces. The model was assessed through comparison with a set of small-scale laboratory test results, and good agreement was found in terms of concentration evolution, uplift onset time, and pipe displacement evolution. The results of numerical parametric studies provide insight into the influence of pipe specific gravity, revealing its impact on the evolving balance between driving and resisting forces—from the onset of flotation to eventual resettlement. The results confirm that, despite the simplifying assumptions, the formulation captures the fundamental physics of pipe flotation and resettlement. The model offers a sound theoretical framework that can support future design-oriented studies aimed at identifying safe combinations of pipe density, trench geometry, and backfilling conditions in offshore installations.

This paper presents the setup, execution, and key findings of a comprehensive centrifuge testing programme investigating the cyclic lateral response of monopiles in sand. As part of the Monopile Improved Design through Advanced cyclic Soil modelling (MIDAS) project, a series of centrifuge tests was conducted using instrumented model piles embedded in both dry and saturated sand under monotonic and cyclic loading, with particular emphasis on very dense, dry sand conditions. The programme examined the influence of pile geometry, load sequence, mean load ratio, and soil density on the accumulation of monopile tilt. Laser displacement sensors, strain gauges, and total pressure sensors were used to measure, or derive, ground-level rotation, rotation point depth, and soil stress redistribution along the pile. The results show that while the maximum accumulated pile rotation is primarily governed by the peak cyclic load, the sequence and asymmetry of loading significantly influence irrecoverable deformation. In very dense dry sand, rotation often stabilised or even decreased with continued cycling, contrasting with previous experimental findings typically associated with looser, though often still dense, sands. The discussion is accompanied by a publicly available dataset, which has supported the development of the MIDAS cyclic soil reaction model for monopiles in sand. This dataset, together with the insights presented herein, provides a valuable resource for researchers and engineers developing or validating design models for offshore foundations subjected to cyclic loading.