Navigating pile refusal challenges in offshore renewables: Data-driven solutions for success

Understanding the risk of pile refusal in offshore renewables 

As offshore renewables expand into deeper waters and tougher seabed conditions, the installation of foundation piles faces increasing uncertainty. Encountering hard layers, boulders or unexpected resistance can halt progress, inflate costs, and delay schedules. At Acteon, we combine data-driven insight with hands-on engineering experience to anticipate, manage, and mitigate these pile refusal risks. 

From data to design: quantifying installation risk 

In the world of offshore renewables and oil & gas industries, finding strategic partners who can seamlessly blend valuable data insights with hands-on practical knowledge is paramount. We pride ourselves on possessing first-hand experience in understanding the unique challenges our customers face. We leverage this experience, coupled with our in-house knowledge base, to provide innovative solutions that meet and exceed expectations. 

In this blog, we explore mitigating the challenges of pile refusal in various soil conditions, which is a critical aspect of subsea installation project planning. Pile refusal is a situation where a foundation pile encounters significant resistance or difficulty during the installation process. This resistance can occur for various reasons, such as encountering hard or rocky seabed conditions, encountering obstacles like boulders or debris on the seabed, or due to challenging geological formations. When pile refusal occurs, it can lead to delays in the construction timeline and increased costs as additional equipment and techniques may be required to overcome the resistance.

Assessing driveability and refusal risk through intelligent engineering 

Data from previously driven piles can be valuable in developing site-specific driving resistance models and calibrating standard driving methodologies. This data can be consolidated into an integrated ground model, often created within a geospatial information system (GIS), and a foundation hazard register (FHR) is established to detail ground risk, both in terms of in-place stability and installation performance specific to the proposed foundation solution. 

The assessment of risk involves various aspects, including pile stability analysis and an evaluation of drivability and the risk of pile refusal and/or pile run. Stability analysis determines the required penetration for safe support and the removal of the pile gripper. A driving (SRD) model, developed using recognised industry methodologies and site-specific data underpinned by practical experience, helps establish a blow count versus depth profile, fatigue assessments, and risk identification. This informs the selection of the optimal hammer size and other equipment to minimise offshore risks and maximise safety.  

Sometimes, modifying the design of the foundation pile itself can help mitigate pile refusal. This may involve changes in pile geometry to better suit the seabed conditions. Our expert geotechnical and structural engineers provide site characterisation, geotechnical and structural consultancy services through 2H, Acteon’s Engineering consultancy, to determine a realistic, cost-effective solution based on individual project requirements.  

Mitigating installation risk with robust solutions 

Addressing pile refusal effectively may involve using specialised equipment, such as vibratory hammers or drilling techniques delivered through Menck, Acteon’s Marine foundations business line, to break through the resistance and securely position the piles into the seabed.  

Impact hammers can be equipped with various types of pile caps and cushions to optimise energy transfer and reduce the risk of pile refusal. Additionally, the blow count can be monitored to assess the pile’s penetration progress. If the installation is performed using vibratory hammers, high-frequency vibrations are used to reduce the friction between the pile and the seabed, making it easier to install the pile. This technique is particularly effective in loose or sandy seabed conditions and can minimise the risk of pile refusal.  

In cases where pile refusal is expected due to challenging geological formations or obstructions, drilling techniques may be employed to help overcome obstacles and reduce resistance. In extreme conditions, equipment such as hydraulic drill rigs or underwater excavation tools may be used to remove obstacles or hard layers before pile installation. High-pressure jetting techniques can also be used to fluidise the seabed sediments around the pile, allowing for easier penetration in certain types of soils.  

During installation, real-time monitoring of pile penetration is essential. Sensors and monitoring equipment are used to assess the pile’s progress, ensuring that any issues related to pile refusal can be addressed promptly.  

Optimised solutions to increase commercial value 

Managing pile refusal is a critical aspect of subsea installation projects in the offshore renewables and oil and gas industries. We stand as a dependable partner, combining practical knowledge with data-driven solutions to navigate the complexities of challenging soil conditions. We understand the risks associated with pile refusal and provide optimised, efficient, and commercially effective solutions that enhance project delivery while reducing overall development risk.  

Early engagement with our customers is central to our approach. This allows us to gain insight into the unique challenges of each project and develop efficient strategies to address the risks associated with the proposed foundation solution. Combined with our in-house knowledge and experience, this proactive approach enables us to meet or improve development schedules while mitigating commercial risk.