How ground conditions influence anchor design for floating wind turbines

Designing anchors for the mooring systems of floating offshore wind turbines (FOWTs) is inherently complex. High mooring loads, combined with challenging and highly variable seabed conditions, mean that anchor selection must be closely tailored to the geotechnical properties of the site. Understanding these conditions early is essential for predicting installation strategy, project schedule, and overall cost. 

Floating wind farms introduce additional complexities due to their scale, environmental exposure, and the need for long term reliability. Ground conditions are a major driver of anchor feasibility, performance, and installation methodology. 

Large site areas with variable soil profiles 

Floating wind developments often span very large geographic areas, leading to significant differences in seabed composition across the site. Soil conditions can vary both laterally and with depth, including transitions between: 

• Soft clays
• Dense sands
• Rock layers
• Mixed sediments 

This variability means a single anchor type may not be technically or commercially suitable for the entire wind farm. Instead, designers must assess how changing soil characteristics influence anchor performance, installation method, and long-term reliability. 

Complex Soil Conditions 

Many planned floating wind projects are located in regions with challenging geotechnical conditions, such as:  

• Rock
• Glacial till
• Very dense sands
• Gravel, cobbles, and boulders 

These ground conditions often require specialised installation techniques, such as drilling or the drive-drill-drive method. Anchor designs that work in soft seabeds may be unsuitable or uneconomical in these environments. 

While developers often have a general understanding of site conditions, the geotechnical influence on anchor design is nuanced. Factors such as strength parameters, layering, stiffness, and drainage behaviour directly affect:  

• Holding capacity
• Embedment performance
• Installation forces
• Long-term cyclic behaviour 

Because floating wind farms span varied terrain, multiple anchor solutions may be needed to deliver a technically robust and cost-effective layout. Achieving this balance requires expertise across both geotechnical engineering and moorings structural engineering. 

A multiphase approach to site investigation 

Acteon supports floating wind developers through a multi phase approach that provides high quality geotechnical data for anchor and mooring system design.  

In situ testing using borehole sampling 

UTEC, Acteon’s Geo-services business line, performs detailed in situ testing using advanced equipment such as the Portable Remotely Operated Drill (PROD5). 

Key capabilities of PROD5 include:  

• Nearly double the tool load capacity of previous systems
• Faster and more cost effective than heave compensated drilling
• Designed for shallow waters (to 500 m)
• Fully capable in ultra deep water up to 4,000 m 

 This allows efficient geotechnical sampling and testing across a wide range of floating wind development environments.  

High quality laboratory testing 

Soil samples are analysed in UTEC’s in house laboratory in Brazil or through vetted third-party labs. Laboratory testing provides reliable engineering parameters, including:  

• Strength and stiffness
• Consolidation behavior
• Particle size distribution
• Rock properties where applicable

Ground condition reporting and characterisation 

UTEC compiles the results into comprehensive reports that map and characterise seabed conditions across the full development area. This dataset forms the foundation of engineering decisions. 

Engineering assessment for mooring and anchor design 

2H, Acteon’s Engineering Consultancy, integrates the geotechnical data into a fully coupled engineering analysis of the mooring system. 

Their assessment includes: 

• Defining engineering soil parameters
• Evaluating anchor feasibility and performance for anchor design
• Integrating geotechnical inputs into structural and hydrodynamic modelling
• Considering longterm cyclic loading, installation forces, and lifeoffield integrity 

This combined geotechnical and structural approach ensures the chosen anchors are suitable for the site’s specific ground conditions, technically robust, and commercially optimised.