What Green Volt reveals about ground investigation in complex geology

Ground investigations play a decisive role in de-risking offshore wind projects, particularly where subsea cables transition onshore at the landfall. In areas with complex or poorly understood geology, relying solely on historical data can bring risks. Investigations must combine site-specific data, geological modelling and specialist expertise to develop an accurate understanding of ground conditions.  

Green Volt represents a major milestone as Europe’s first commercial-scale floating wind farm and for offshore wind. Beyond the turbines and infrastructure, one of the more challenging problems that needed to be solved was where offshore and onshore meet. This is known as the landfall.  

The project’s landfall, at Craigewan Links near Peterhead, connects the seabed infrastructure to a 35km onshore cable route across Aberdeenshire, an area with sparse intrusive investigation data. Designing a ground investigation for the cable route meant working with limited historical data in highly variable, notoriously complex geology, which could have resulted in significant project risks.

Addressing these uncertainties called for more than robust technical analysis. The team combined research, modelling and insights from local landowners and academics so every decision was informed by on-the-ground realities and underlying geology.  

How to build a reliable ground model from limited data

Green Volt sits within one of the UK's geological exceptions. Historical ground investigation data is sparse, and, in some cases, the published geological mapping was inaccurate.

The team adopted an iterative and evidence-led approach rather than relying on what went before. Drawing on experience from comparable projects, academic research, site-specific investigations, and geological know-how, they developed a comprehensive, predictive ground model.

As boreholes were drilled along the route (often out of sequence), the subsurface began to reveal its complexity, and the ground model was tested. This part of Scotland contains some of the UK’s oldest and most geologically complex rock formations. These were created by multiple phases of volcanic events, tectonic movement and glaciation, in ways that can appear contradictory at first glance. The shallow, superficial soils featured numerous buried glacial and post-glacial channels, often not mapped or recorded, and consisted of significant thicknesses of clays, sands, and gravels.  

Each layer encountered contributed to an evolving understanding of the ground and led to multiple revisions to the ground model, progressively reducing uncertainty and informing design decisions along the route.  

The project showed the importance of remaining adaptable throughout an investigation.

A landscape that continues to challenge assumptions

As the investigation developed, it became clear that the geology's variability was highly localised. Changes in ground conditions occurred both laterally and vertically over short distances, further complicating interpretation.  

Metamorphic rocks, altered by heat and pressure, cover much of the region. However, the types of metamorphosis varied widely. Spotted rocks, such as pelite (a sedimentary rock) containing cordierite prophyroblasts (mineral crystals), were found between massive psammites (sandstones). As a result, some of the psammites were completely eroded and so structurally weak, whilst others remained untouched and strong.  

Additional findings reinforced how even experienced teams can be challenged by complex ground conditions. Coarsely crystalline pegmatites (igneous rocks) were identified with the country rock (the existing rock formation). These were originally mis-recorded due to a fault and so required collaboration with academic specialists to confirm the initial interpretations and produce the ground model.  

The superficial soils introduced additional geotechnical challenges. Unrecorded, buried glacial channels posed new challenges to the investigation and subsequent design. These were often poorly consolidated and of significant thickness, which needed to be addressed.  

These discoveries show that assumptions - even in familiar terrains - can be misleading. Investigations must remain flexible and adapt to on-site findings.  

From investigation to informed delivery

By the end of the investigation, the team had completed around 300 boreholes along the 35km route. This provided a substantial volume of data but also revealed how complex it was to translate that data into a coherent and reliable ground model.  

Working with academic experts was key to interpreting the findings, especially for understanding the associations among igneous, metamorphic and structural geology across the site. Evidence of multiple phases of volcanic and seismic activity, alongside both contact metamorphism and regional metamorphism, confirmed the area as one of the most geologically diverse in the UK.

Due to the extensive variables, the project required a detailed, adaptable ground model to better manage risk and deliver Green Volt to construction. The key takeaway is that expanding offshore wind requires ground investigations to uncover unknowns, not just confirm assumptions.

Success now depends as much on challenging assumptions and integrating diverse knowledge as on technical skills.  

Green Volt demonstrates that the ground investigation is not simply a confirmatory tick-box exercise. It is a critical part of determining how major renewable infrastructure is de-risked and delivered effectively and efficiently. 

If you’re navigating complex ground conditions on renewable energy projects, early-stage infrastructure and integrated thinking can make a significant difference to risk, design and delivery outcomes. Contact a member of our energy team to learn more.