Skirt–pile foundations have gained widespread attention in the field of offshore engineering due to their ease of installation and high bearing capacity. In this study, the ultimate bearing capacity, pile bending moment distribution and development, cumulative deformation characteristics, and cyclic stiffness development of skirt–pile foundations were investigated using physical model tests. The experimental results indicate that the ultimate bearing capacity and deformation resistance of the foundation can effectively be improved by increasing the skirt diameter. The cumulative deformation of the skirt–piles exhibited rapid development during the initial stages of cyclic loading, eventually stabilizing. Under long-term cyclic loading, the existence of the skirt can share the bending moment, which then affects the internal force distribution of the pile foundation along the axis. The pile foundation’s cyclic stiffness reduces as the loading cycles increase and increases as the skirt diameter and length grow. Meanwhile, the horizontal cyclic stiffness decreases as the number of cycles increases, stabilizing after 3000 cycles. This study can not only deepen the understanding of the deformation laws of skirt–pile foundations in clay soil but also offers some references for the design of offshore pile foundations.

In order to study the failure mechanism of a finned pile foundation under horizontal cyclic loads, a physical model test of the pile–soil interaction of finned pile is designed in this paper. Based on the model tests, the pile top displacement, the cyclic stiffness of the pile foundation, and the response of pore water pressure within the soil around the pile were fully studied for the finned pile foundation under horizontal cyclic loads. It is found that the cyclic stiffness attenuation of the finned pile foundation is more severe than that of a regular single pile foundation, but the final stiffness at equilibrium is still greater than that of a regular single pile foundation. The accumulation of horizontal displacement at the pile top and pore water pressure within the soil around the pile mainly occurs in the first 1000 loading cycles, and an increase in fin plate size will reduce the magnitude of pore water pressure and pile top displacement. This study can not only deepen the understanding of the failure mechanism of finned pile foundation under horizontal cyclic loads, but also provide guidance for the design of the finned pile foundation.

In this paper, a two-dimensional numerical model for wave-seabed-pipeline interaction is developed to examine the wave-induced uplift force onto pipelines buried in sloping seabeds. The Reynolds-averaged Navier stokes equation and the poro-elastic equation are used to simulate the wave motion and seabed response, respectively. Meanwhile, the pipeline is considered to be elastic. Firstly, three laboratory experiments are taken to verify the effectiveness of the numerical model. Then, the effects of pipeline characteristics, soil properties and wave parameters on the nonlinear wave-induced uplift force onto a pipeline buried in a sloping seabed are analyzed. Finally, an empirical formula for predicting the nonlinear wave-induced uplift force onto buried pipelines under different slope angles is proposed. It can be found that the slope angle can greatly affect the nonlinear wave-caused pore pressure response, as well as the uplift force onto the pipeline. Moreover, the simple method for predicting the uplift force proposed in this paper can facilitate engineering applications.

As a new type of offshore wind power foundation, skirt–pile foundation combines the advantages of pile and bucket design, which can effectively control the horizontal deformation of the foundation. In addition to being subjected to dynamic loads such as wind, waves, and earthquakes, wind power foundations are also affected by vibrations caused by turbines, and their erosion evolution mechanism is very complex. This article investigates the erosion development process around skirt–pile foundations under vibration combined with steady water flow, vibration only, and water flow only conditions through flume experiments, with a focus on the influence of vibration frequency and amplitude on the ultimate equilibrium scour depth and scour hole morphology. Experimental results show that the vibration–flow coupling effect can affect the scour depth and the scour morphology around the foundation by changing the compactness of the soil and can accelerate the formation of scour equilibrium through. Compared with water-only scouring, the foundation scouring under coupled vibration–flow condition reaches equilibrium in a shorter time and has a smaller erosion depth. Moreover, increased vibration amplitude results in wider but shallower scour holes with more uniform shapes. Higher vibration frequencies correspond to decreasing scour depth, radius, and slope. Overall, scour characteristics exhibit a negative correlation with vibration intensity, with the influence diminishing at greater azimuthal angles. Based on the measured result, a formula for forecasting the equilibrium scour depth of skirt–pile foundations under combined vibration–flow actions was proposed. The research can provide a basis for predicting scour depth of skirt–pile foundation under the coupling effect of vibration and flow.

The structure dynamic characteristics determine the response, vibration behavior, and long-term usability of the foundation to external loads; quantitative identification of its driving factors is crucial for precise design, safety optimization, and fatigue life prediction. In harsh marine environments, local erosion around offshore foundations can significantly alter dynamic performance. Previous studies linked the depth of scour to changes in pile fundamental frequency, but largely overlooked the additional effects of scour pit morphology and hydrodynamic forces. This study established a fully coupled fluid soil pile interaction model with dynamic grids to capture real-time erosion evolution and validated it through comprehensive flume measurements. Then, the system analyzed and quantified how current velocity, water depth, and scour pit geometry collectively affect the natural frequency of the foundation. The results indicate that for maximum scour depths below 1.8 times the pile diameter, it is not sufficiently accurate to explain the frequency attenuation by considering only the maximum scour depth while ignoring scour-pit morphology. Neglecting hydrodynamic effects may result in an estimated fundamental frequency difference of up to 20% for scour pile foundations.