The Construction Conditions of a Pre-Piling Template for Foundations of Offshore Structures

Abstract

The foundations of offshore wind power can be classified as floating, tripod, jacket, monopile, or gravity-based, depending on the support type. In the case of tripod- and jacket-type supports, the structures require precise construction. There are two main methods for installing substructures: post- and pre-piling. The post-piling method involves moving the completed substructure to the site and fixing it to the seabed by inserting a pile into the leg pile and driving it, allowing it to be constructed without special off-shore equipment; however, the construction period is long. Contrarily, the precision of foundation installation can be improved by installing a pre-piling template, which is special equipment that serves as a basic structure, on the seabed in advance, and subsequently inserting substructures. This study presents a new type of underwater pre-piling template and method for achieving optimal construction environment conditions. Construction precision was analyzed based on the wave condition, current speed, winch speed, wave direction, and current direction while the under-water template was anchored to the seabed. It was found that the wave conditions, winch speed, and vessel type had a significant influence. The results obtained considering the Douglas sea scale show that precise construction could only be achieved within Grade 2 for general barge ships, while jack-up barge ships could be used even at Grade 3 or higher. The higher the winch speed, the more stable construction becomes possible, and jack-up barges show greater constructability than general barges.