Yijun Ge

The current research on the penetration of offshore wind turbine monopiles primarily focuses on driving with a vibratory hammer, although there are several smaller studies that focus on the vibrating penetration mechanism. To further the body of research, this paper establishes a numerical model to calculate the vibration penetration speed (VPS) of an offshore wind turbine monopile that considers the soil plugging effect. In this model, a monopile is assumed to be a rigid body. The surrounding soil is divided into a series of circular cylinders of concentric axes. The shear stress at the external soil elements' interfaces and the soil's vertical stress at the monopile toe are calculated using the Gudehus–Bauer hypoplastic constitutive model. The VPS is obtained from the motion equation by compiling it in MATLAB R2012b. Finally, a finite element model is conducted to verify the results, showcasing the rationality of the proposed model. Parameter analyses are also conducted to study the influences of the soil void ratio, soil internal friction angle, vibration frequency, ratio of static load to dynamic load, and monopile diameter on VPS.

Compared with the conventional drainage strengthening techniques, the precast concrete segment assembly strengthening method (PCSAM) is regarded as a fast, more economical, and traffic-friendly underwater strengthening method for damaged bridge piers and piles, as the drainage procedure can be omitted. However, this method still has some disadvantages, such as strength loss of the filling material, debonding of the interface due to shrinkage of the filling material, poor connection effects, and poor durability of the segment sleeves. To solve these problems, the PCSAM is improved in this study by using self-stressed anti-washout concrete (SSAWC) as the filling material and by developing a lining concrete segment sleeve (LCSS) by referring to the design theory for shield lining segments. Six specimens are designed and prepared with consideration of the influential factors, such as the self-stress, thickness of the filled concrete, and concrete strength of the LCSS, then the monotonic axial compression test is carried out to investigate the improvements in the axial compression properties of the specimens. Accordingly, extended parametric analyses are performed based on the established numerical models. Finally, the calculation formula for the bearing capacity is proposed based on the analysis results. The results indicate that the SSAWC can provide initial confining compressive stress in the core region of the piers, in addition to increasing the bearing capacity and ductility of the specimens. The improved LCSS segment connection is more reliable and increases the strengthening efficiency. The influence of self-stress on the bearing capacity of the specimens is cubic and the influence of the filled concrete strength on the bearing capacity of the specimens is nonlinear. The calculation formula for predicting the bearing capacity of axially compressed columns possesses good applicability and can be used as a reference for practical engineering.