Yukun Ma

With the rapid development of offshore wind turbines, traditional monopiles have increasingly exhibited performance limitations. In recent years, plate-monopile hybrid foundations and bucket-monopile hybrid foundations have attracted growing attention due to their structural simplicity and ease of fabrication. However, existing studies have mostly investigated these two hybrid foundation concepts independently, and systematic comparisons under comparable conditions remain lacking, particularly with respect to their soil-pile interaction behaviours. Based on the principle of equal material consumption, this study conducts a series of 1 g scaled model tests combined with prototype numerical simulations. The aim is to comparatively investigate the mechanical response differences and pile-soil interaction mechanisms among monopile, plate-monopile hybrid foundation and bucket-monopile hybrid foundation. The results indicate that: (1) Under the principle of equal material consumption, adjusting the baseplate diameter and wall embedded depth of bucket can yield an optimum configuration that provides larger bearing capacity than the plate-monopile hybrid foundation; (2) Compared to the plate-monopile hybrid foundation under identical loading amplitude, the bucket-monopile hybrid foundation shows 30% less deflections at mudline level and 60% greater cyclic stiffness across the considered parameter range; (3) With increasing number of loading cycles, an upward shift of the pivot point is observed for all hybrid foundation configurations. The bucket-monopile hybrid foundation exhibits the most notable response; (4) High loading amplitude and long-term cyclic loading amplify the ability of bucket-monopile foundation in reducing the structural bending moment and shear force. The experimental and numerical studies are expected to provide new insights into the mechanical behaviour of the hybrid pile foundations to support their optimal design.

The plate-monopile hybrid foundation is a cost-effective solution for supporting offshore wind turbines under complex conditions. In this study, FE models of hybrid foundation and monopile are established. Taking the Walney Wind Farm as a test site, the dynamic responses of two foundations under different loading patterns (symmetric bidirectional, asymmetric bidirectional, fully recovered unidirectional, partially recovered unidirectional) and different load amplitudes (0.3-0.7 of ULS load) are comparatively analysed. The results indicate that: (1) The hybrid foundation achieves a normalised deflection ratio as low as 0.78 and stiffness as high as 1.28 of the monopile; (2) The evolution pattern of deflection under bidirectional symmetric cyclic loading differs from other patterns; (3) The vertical effective stress beneath the plate is single-peak distribution under partially recovered unidirectional loading but double-peak distribution otherwise; (4) The hybrid foundation reduces the peak bending moment and shear force by up to 10% and 20% per unit load, respectively, and shifts their locations upward along the embedded depth; (5) The contribution of the steel plate increases with cycle number and load amplitude. This study provides new insights into the mechanical performance of the hybrid foundation under dynamic loading.

The plate-monopile hybrid foundation, owing to its structural simplicity, cost-effectiveness, and potential for life extension, has emerged as a promising alternative to monopile in complex marine environments. However, its mechanical performance and soil-structure interaction mechanisms under unidirectional cyclic loading remain insufficiently investigated. In this study, the Walney Wind Farm is as a test site, FE models of monopile and plate-monopile hybrid foundation are established to comparatively analyse the mechanical responses under fully recovered and partially recovered unidirectional cyclic loading, to evaluate the improvements in performance of the hybrid foundation, and to elucidate the soil-pile interaction mechanisms. The results indicate that: (1) The hybrid foundation reduces the accumulation of peak and residual deflection, with distinct evolution patterns under fully recovered and partially recovered unidirectional cyclic loading. (2) Unloading stiffness of the hybrid foundation exceeds that of monopile and resists degradation more effectively, particularly at higher loading amplitudes. (3) Stress distribution beneath the plate and around the pile shows clear double-peak features under fully recovered unidirectional loading, which diminish or evolve into single-peak distributions under partially recovered unidirectional loading. (4) The hybrid foundation suppresses the accumulation of bending moment more effectively than shear force.

In recent years, with the growing attention to offshore renewable energy, hybrid offshore renewable energy harvest system (HOREHS) has gradually emerged as a promising solution. These systems enable cost-effective harvest of offshore renewable energy and hold significant potential in contributing to the achievement of the United Nations Sustainable Development Goals. Since the concept remains at the early stage of development, there is a lack of systematic summary of challenges and latest development of these systems. This paper provides a comprehensive review of progress made in relation to this novel hybrid systems, including integrations approaches of diverse energy harvesting devices and various support technologies. The characteristics and limitations of different types of hybrid systems are compared and summarised. This paper then reviews the numerical simulations approaches and physical testing techniques for testing HOREHS and the mechanical responses of HOREHS obtained from these investigations, which demonstrate the feasibility of hybrid systems from the perspective of mechanical response. Finally, the paper outlines the potential challenges that HOREHS may face in the future.

Establishing a hybrid offshore renewable energy harvest system (HOREHS) on a shared platform can reduce energy costs and increase productions. This paper aims to propose a HOREHS supported by a foundation consisting of a monopile and a plate to integrate various offshore renewable energy devices. Taking the Sheringham shoal wind farm as a case study, the benchmarking monopile dimensions were determined using design guidance and an equivalent monopile-plate combination was determined from FEM simulations. Parametric studies of system mechanical responses were conducted using FEM simulation. It is found that, to maintain the same mechanical response, the embedded depth of the monopile supporting the HOREHS should be increased by about 17% comparing with that supporting an offshore wind turbine. Adding a 14 m diameter steel plate can avoid the extra 17% embedded depth. Adding a plate has no effect on the size of influence zone of lateral soil stress. However, due to the shorter embedded depth, the magnitude of lateral stress for the hybrid foundation is larger than that for monopile, with the maximum increase being about 18%. The system response at the mudline level shows the highest sensitivity to the changes in embedded depth and plate diameter.

A hybrid offshore renewable energy harvest system (HOREHS) integrates multiple offshore renewable energy harvesting devices into a shared platform, offering a promising solution to enhance energy sustainability. Selecting a foundation with high performance and understanding system response are essential for ensuring the stable operation of the HOREHS. This paper examines a HOREHS supported by a hybrid foundation consisting of a steel plate and a monopile. The Walney Wind Farm was selected to conduct a comparative numerical investigation. FE models of HOREHS supported by monopile and hybrid foundation were established. The responses of the upper structure and the soil-foundation interactions under dynamic loading were analysed. The results show that (1) The hybrid foundation significantly reduces the deflection at different levels and changes the trend of deflection variation with increasing cycles compared with monopile; (2) The presence of the steel plate alters the distribution of both the peak and residual lateral soil reaction forces and increases the shallow soil stress near the pile; (3) The presence of the steel plate reduces peak shear forces, shifts their maximum positions upward, and decreases the peak bending moment; (4) Cyclic loading alters the system natural frequency and damping ratio, and the presence of the steel plate modifies their evolution trends with increasing loading cycles. The results provide exploratory, mechanism-oriented insights under the investigated modelling assumptions, advancing engineers’ understanding of the underlying mechanisms. 

The plate-monopile hybrid foundation is an innovative solution developed to support increasingly larger offshore wind turbines under harsher marine conditions. However, due to its structural differences from monopile, the bearing capacity estimation model and failure mechanisms remain unclear. In this study, FEM simulations were performed to obtain the bearing capacity of the hybrid foundation for various soil parameters and foundation geometries, covering representative worldwide seabed conditions as well as current and future design parameters in the offshore wind industry. The failure envelopes of the hybrid foundation under different parameter combinations were established, and the empirical formulas for estimating the ultimate bearing capacity were derived based on extensive simulation results. The results indicated that (1) Both lateral load bearing capacity () and moment bearing capacity () were positively correlated with soil properties and foundation geometry, with consistent parameter effects. (2) The failure envelope of the hybrid foundation in the -plane exhibited an elliptical shape, and variations in different parameters affected the curvature of the envelope to distinct extents. (3) The applicability of the proposed bearing capacity prediction formula for the hybrid foundation incorporates both soil properties and foundation geometric parameters was quantitatively validated against previous research cases.

Low-temperature degradation affects the bearing capacity of rock-lining constructions surrounding tunnels in chilly regions. In this work, rock-concrete composites with varied interface angles (0°, 30°, 45°, 60°, 90°) were tested for freeze-thaw (F-T) cycles (0, 4, 8, 12, 16) and uniaxial compressive strength. The impact of F-T cycles and interface angles on the strength degradation of composite specimens was quantitatively evaluated. The microscopic degradation mechanisms induced by F-T cycling were analyzed using scanning electron microscopy. According to the experimental findings, the F-T mass loss rate of the specimens followed a power-law distribution. Under the influence of F-T cycles, the peak strength loss rate reached a maximum of 40%. Under the influence of the interface angle, the elastic modulus of specimens subjected to different F-T cycles displays varying trends. Finally, an innovative damage constitutive model was developed that couples the evolution of F-T damage with the effects of interface angles. The model is applicable for predicting the impact of F-T cycling on the durability of rock-concrete structures, which provides effective support for the long-term performance evaluation of the structure.