bespoke testing unlocks early insights for Awel y Môr

RWE is leading the development of the Awel y Môr offshore wind farm, on behalf of a group of partners, in the Irish Sea and required early insights on the seabed conditions to ensure the subsurface rock would be suitable and safe for the construction of the turbine foundations.

Often developers postpone planning until spring due to concerns about winter site works. But, as with many major infrastructure projects, efficiency in the planning and design timeline was key. We worked closely with RWE to ensure the GI could be safely and successfully conducted during winter. This was achieved through meticulous planning and execution, plus the careful selection of the right mission-specific equipment.

Winter-proofing operations

The project presented several significant challenges, including a short lead time, deep water operations, inclement weather and unpredictable tidal velocities and ranges during the winter months. We had to tailor our plan for high winds, rough seas, and low temperatures in the Irish Sea that could potentially disrupt operations.

The campaign was carried out in two phases, the first for the offshore substation locations, followed by the wind turbine generator locations.

Given the constraints, we mobilised a self-elevating liveaboard jack-up barge (JUB). JUBs are suited to coastal environments as the legs are fixed to seabed and don't move with the waves. Additionally, our metocean team, provided advanced weather forecasting tools so we could plan activities around favourable weather windows.

The investigation involved drilling 53 boreholes over a period of 130 days, with water depths reaching up to 37 metres. The scope included in situ testing techniques, such as:

• Wireline geophysical logging, for example, high-resolution acoustic borehole imaging for discontinuity mapping and structural evaluation of the underlying strata, P- & S-wave suspension logging, caliper and natural gamma methods

• Wireline cone penetration testing (CPT)

• High pressure dilatometer

• Optional top push CPT.

Our bespoke 20" conductor hostile environment riser casing was selected for the project as it allows the drill string to remain in place through inclement weather events. This saved time compared to traditional casing systems that pull the casing up prior to a weather event, then re-drill to test depth afterwards.

Health and safety considerations

Allowing staff to live onboard the JUB for the duration of the project reduced the need for frequent crew changes and the potential HSSE risk and downtime.

Our bespoke riser casing system eliminates manual lifting and reduces the need for operatives to interact directly with the equipment. The automated system is designed for tough environments and makes it easier and safer to install long sections of large casing to stabilise the boreholes.

Additional laboratory testing

When we began the laboratory testing for Awel y Môr, we found the Mercia Mudstone rock was more complex than expected; its variability and broken nature made traditional rock testing methods, such as uniaxial compressive strength and point load testing, less effective. To obtain better results, we recommended to RWE and their consultant, GCG, other testing (rock triaxial) which is more suited to the rock type and provides a greater understanding of its strength. This led to an innovative, expanded campaign, combining techniques that haven’t been previously used together in our laboratory.

This tailored methodology included triaxial and oedometer testing to better understand the rock strength. We also carried out Atterberg testing – usually reserved for clays - but in this case applied to the mudstone to see if it behaves like a soil or non-plastic sand. The triaxial testing provided a more accurate understanding of the rock's strength by adding confining pressure, which better simulates the rock's natural conditions.

Collaboration with GCG was crucial in scheduling and conducting the testing. The team has worked closely with the laboratory to develop new methodologies, adapting quickly. This highlights Fugro's unique capabilities and commitment to delivering high-quality data even in complex environments.

Proven capabilities for future projects

Our ability to adapt to the challenging conditions and maintain high standards of safety and efficiency was instrumental in the project’s success. Collaborating with RWE on developing a solution to suit their needs, combined with our team’s expertise and meticulous planning, ensured that the investigation was completed despite the difficult winter environment.

We improved our understanding and experience in the complexities of the coastal subsurface and testing methods for intricate geologies; greater knowledge that we can bring to future clients and projects.

It also proved that GI campaigns can be conducted at any time of year. Indeed, planning your investigation during autumn or winter can avoid potential spring-summer backlogs, to keep your project on schedule.