Study on Meso-Structural Evolution of Bedrock Beneath Offshore Wind Turbine Foundation in Pressurized Seawater

Abstract

In recent years, offshore wind turbine technology has been widely developed, making a significant contribution to the advancement of renewable energy. Due to the predominant subsurface geological composition characterized by rocky formations in some marine areas, rock-socketed piles are commonly applied as offshore wind turbine foundations. Generally, rock-socketed piles need to be driven into rock layers that have not undergone significant weathering or erosion for optimal load-bearing capacity. This design is essential to ensure structural support for offshore wind turbines. However, during the long-term operation period of offshore wind turbines, the contact surface between the rock-socketed pile and the rock is prone to be detached under multiple dynamic loads. The generated channel makes seawater seep into the unweathered rock layer, resulting in the erosion of rock meso-structure and deterioration of mechanical properties. The reduced load-bearing capacity will adversely affect the operation of the offshore wind turbine. In this study, the meso-structural evolution of bedrock in pressurized seawater is investigated by X-ray CT imaging using tuff samples from the marine areas of an offshore wind farm in China. A cellular automata model is proposed to predict the long-term evolutionary process of tuff meso-structure. Results indicate that the porosity of the tuff sample in the pressurized seawater shows an upward trend over time. Based on the erosion rate of pores obtained from the CT scanning test, the proposed cellular automata model can predict the evolutionary process of tuff meso-structure and corresponding failure strength of the bedrock in the long term.

A New Ocean Rock Mass Rating and Its Application to Determine the Ultimate Bearing Capacity of an Offshore Wind Monopile Foundation

“…These original rock mass classifications are unsuitable for evaluating the quality of the marine bedrock because the effect of time of seawater erosion on the deterioration of rock properties is not considered. Zhang et al [16] pointed out that in recent offshore wind turbine foundation designs, the evaluation is typically assessed without considering seawater erosion. It is recommended to adjust the original rock mass classification and consider the effect of time of the seawater erosion.…”