ISP-Bucket: Development of an in situ testing method for suction bucket foundations of offshore wind turbines

At a glance

• Compared with other foundation structures, suction bucket (or suction caissons) offer the advantage that they can be installed in the seabed with minimal noise emissions .
• However, to overcome installation refusal in difficult soil conditions, reactive measures during the installation can be required. Currently, there is no approved test method available for the reliable assessment of the load-bearing capacity and stability of suction bucket foundations following the implementation of these measures.
• The ISP-Bucket research project aims to close this gap and thus deliver an important basis for the further development of suction buckets as a reliable offshore foundation element, emphasizing their low-noise installation method.

The challenge

Suction bucket foundations are increasingly being employed in the offshore wind industry alongside the monopiles already in widespread use. This environmentally friendly foundation structure allows almost silent installation, flexible production, and complete dismantling. However, challenges due to unexpected obstacles and varying seabed conditions can occur during the suction-assisted installation at sea. The installation process must then be adjusted ad hoc, for example by means of pressure cycling or repositioning. These adjustments can affect the load bearing behavior of the foundations considerably. To date, there is no approved in situ test method for suction buckets to estimate such changes.

The solution

The aim of the ISP-Bucket project is to develop a test method that enables reliable assessment of the axial load-bearing capacity and stability of suction bucket foundations after installation. To achieve this, the researchers are evaluating existing data on suction bucket installations performed at IWES at different scales retrospectively and also expanding on test results from the ProBucket project. The findings will be used as a basis for executing a complementary small-scale test campaign at the Test Centre for Support Structures Hannover (TTH). As a result, a correlation approach that considers the effects of installation and dismantling pressures will be developed. This approach will be verified and optimized based on the test results generated in the project. 

The added value

ISP-Bucket represents key progress in the further development of suction buckets as a reliable and quiet offshore foundation technology. In the future, operators of wind farms will have a tool at their disposal allowing cost-effective and low-risk planning of wind farms, in particular with regard to noise protection regulations in the German Exclusive Economic Zone (EEZ). Furthermore, the newly developed test method will make it possible to corroborate and optimize design assumptions, which can enable more reliable predictions of bucket performance and thus contribute to lower economic costs of offshore wind energy use.