Piled-cruciform attachment to monopile head reduces deflection

Much critical infrastructure, including bridges, wind turbine structures, dolphins and some other ocean engineering structures, is supported on large-diameter rigid monopiles. For such structures, compared with the gravitational loads, cyclic lateral loading may often be more critical for the analysis and design. The lateral load-carrying capacity of a pile depends on its geometry (dimensions), the soil properties and type of loading. In order to increase its lateral load-carrying capacity, it is necessary either to change the properties of the near-surface layers of soil or to change its geometry. This paper presents model studies investigating a novel technique to limit the lateral deflection (rotation) of a monopile under long-term cyclic lateral loading. The technique provides enhanced restraint of the monopile through the installation of four shorter piles, arranged in a cruciform, which attach to the head of the central monopile by way of a grillage. Different aspects of this modification, including its fabrication and attachment to the monopile, are presented. Its efficiency in reducing the monopile rotation under cyclic lateral loading is evaluated through a comprehensive testing programme, with reasonably encouraging results.