Penetrating-levelling tests on bucket foundation with inner compartments for offshore wind turbines in sand

Abstract

The penetration of a bucket foundation in sandy soil is complex. When suction is large, the installation of bucket foundation is prone to seepage damage, and the foundation cannot penetrate the sandy soil due to insufficient suction. The impact of the skirt plate and inner compartment plates in mono multi-chamber bucket foundations on the penetration resistance is not clear. In addition, when the foundation is tilted, whether it can be leveled to the design requirements is related to the success or failure of the installation. When the suction during leveling reaches the critical value, penetration damage will occur; therefore, selecting the correct leveling strategy is particularly important. This paper primarily deals with the issue of mono multi-chamber bucket foundation penetration and the associated leveling mechanisms, focusing on analyzing the influence of the skirt plate and inner compartment plates on mono multi-chamber bucket foundation penetration resistance, selecting the mono multi-chamber bucket foundation leveling method, and analyzing the relationship between the adjustable angle and depth in the bucket foundation leveling process. Moreover, the seepage characteristics of the soil under the leveling state is studied, and the critical suction is derived. The analysis results show that the leveling method of applying suction to multiple chambers is safer than the method of applying negative pressure suction only on one chamber. In addition, the negative pressure leveling method has a certain limitations on the inclination angle and penetration depth. To the bucket foundation test model, when the foundation inclination angle is less than 2° and the ratio of penetration depth to skirt height is within 0.5, the foundation can be leveled using negative pressure suction on the high chamber. The reason for the failure of leveling is the formation of piping channels. When seepage failure occurs, the permeability coefficient of the soil in the high chamber may be about 10 times that of the soil that is not affected by suction.