Drilling solutions for offshore wind foundations and export cable landfalls

Abstract

The development of renewable energies is the focus for future energy supply. Large offshore wind farms are to be constructed and connected to the grid. Due to public environmental awareness, smart methods are required for fast and safe installation of foundations and cable landfalls. In addition to limitations in certain ground conditions, conventional pile-driving has a deep environmental impact and reaches its limits with increasing turbine sizes and water depths. Today, the Offshore Foundation Drilling technology provides a completely drilled installation of offshore foundations. Both full-face cutting systems and partial-face excavation concepts are utilized, depending on the foundation type and diameter to be installed. While partial-face excavation solutions are primarily used for drive-drill-drive installations of tapered monopiles, the OFD full-face machines are mainly considered for rock socket drilling and drive-drill-drive of pin piles, providing high drilling performance and considerably reduced acoustic emissions. For the connection of offshore wind farms to the onshore grid, microtunnelling methods offer considerable environmental, safety benefits and a high degree of flexibility for project planners and contractors. Landfall sections of export cables are usually located in sensitive coastal areas with high environmental regulations. Remote-controlled microtunnelling methods like Pipe Jacking and Direct Pipe are used to safely install protective pipes and tunnels with subsequent pull-in of the export cables. Drilling works are carried out underground, from onshore to offshore, to reduce marine construction costs and to preserve marine wildlife and seawater quality. This paper shares different technological approaches for trenchless landfall construction and offshore foundation drilling. 1 No-Dig Down Under 2025 Drilling solutions for offshore wind foundations and export cable landfalls Ben Hayes, Dr. M. Peters and Joachim Engelhardt 1. OFFSHORE FOUNDATION DRILLING WITH OFD® With a growing number of offshore installations for the expansion of renewable energies and the construction of coastal infrastructure, the demand for an economical and environmentally friendly installation technique of offshore foundations has gained importance in recent years. More and more foundations have to be installed for wind turbines, transformer stations, tidal power plants, bridges and harbor infrastructure, such as quay walls, breakwater and jetties. Today, the main focus for the Offshore Foundation Drilling (OFD) applications are the wind farm foundations, including anchoring of floating wind turbines, with drilling diameters from 3 to 12 meters. 1.1. Benefits of drilled approach for foundations Based on more than 40 years of experience in the tunnelling industry, OFD drilling concept represents a customized drilling technique, according to foundation diameter and specific project conditions. The continuous drilling process with constant diameter to install the foundation directly or indirectly in the seabed is executed by the cutterhead of the machine. The cutterhead is equipped with cutting tools and further customized according to specific project conditions. Extendable overcutters enable under-reaming to assure a smooth lowering of the drilled structure (e.g. final pin pile foundation) or temporary casing structure, depending on the installation method of the foundation. The high-torque machinery provides high performance rates and continuous control of the discharge volume by frequency-controlled slurry pumps. This makes the OFD technology highly competitive and reliable with a high level of safety standards and low noise emissions at the same time. 1.2. Bottom-fixed drilling solutions In OFD both full-face cutting systems and partial-face excavation concepts are utilized, depending on the foundation type and diameter to be installed. While partial-face (PF) excavation solutions can primarily be used for drive-drill-drive installations, the OFD full-face (FF) machines can be considered for socket drilling for monopile and pin pile installation and drive-drilldrive approach for pin piles. Figure 1. Overview of mechanized drilling approaches for bottom-fixed foundations. 1.2.1. Pin Piles and Jackets (FF) The application of pin pile installations with full-face OFD typically involves two main installation methods. The first is socket drilling with underreaming, where an annular gap is created by drilling a larger diameter than the pile’s outer diameter. This is achieved using either a temporary casing or the final pile itself as the drill guiding. Once the desired depth is reached, the annulus is filled with grout to ensure structural stability and effective load transfer to the surrounding ground. 2 No-Dig Down Under 2025