Analysis of Settlement Behavior and Evaluation of Field Applicability of an Underwater Template Using the Pre-piling Method

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Offshore wind energy, as a large-scale renewable energy source, is continuously seeing an increase in project developments, particularly centered around Europ. Due to the recent increase in interest in renewable energy, new developments are underway in the southwestern coastal area to achieve a supply of 12GW of offshore wind power by 2030. As the scale of offshore wind farms becomes larger, the technology for installing offshore wind substructures has become crucial. The pre-piling method, which utilizes an underwater template that serves as a framework for precisely installing piles in the seabed, is advantageous for large-scale farms due to its short construction period and the ability to move and install piles using a single template. This method has seen increasing demand, and research on the design and construction technology of pre-piling methods, as well as underwater templates, is actively being conducted.Existing underwater templates pose a risk of settlement and differential settlement on soft ground, potentially making it impossible to meet the horizontal installation standard of 0.25° required for offshore wind turbine installation. This study compares the traditional underwater template with a new underwater template equipped with a skirt foundation designed for installation on soft ground and to ensure horizontality despite differential settlement. Based on numerical analysis results, we developed a leveling technology that uses multiple hydraulic cylinders to control horizontal and vertical alignment. Since excessive settlement can make it challenging to maintain the horizontality and verticality of the pockets of the underwater template on very soft ground, we fabricated a separate structural form with a tripod skirt foundation for use on such grounds. We then tested the leveling and individual sensor and module performance of the underwater template using the pre-piling method.