Case Study: Cumbrae Solar Array, Great Cumbrae
Client: Advance Grid Solutions Ltd
Services: Geoenvironmental site investigation, trial pitting, geotechnical laboratory testing, pile installation, pre-drilled and grouted piles, pull-out testing, compressive and lateral load testing, corrosion assessment, foundation recommendations
Location: Great Cumbrae, Scotland
Project summary & client purpose:
Earth Environmental & Geotechnical was commissioned to undertake a geoenvironmental site investigation to support the development of a ground-mounted solar array on Great Cumbrae, Scotland. The proposed scheme comprised 142 solar array modules and associated infrastructure.
The investigation was designed to establish ground conditions across the site, assess the suitability of proposed foundation solutions and evaluate the potential for steel corrosion. The findings provided the client with the information required to optimise foundation design and reduce construction risks before installation commenced.
Our services:
Our team completed a comprehensive programme of exploratory works, including 21 machine-excavated trial pits across the site to assess subsurface conditions. Geotechnical laboratory testing was undertaken alongside chemical testing to determine engineering properties and ground aggressivity.
Following the initial site investigation, we continued to support the project through a second phase of works, installing pre-drilled and grouted piles before undertaking pull-out, compressive and lateral load testing to validate the proposed foundation solution.
In total, 36 ‘C’ section piles were installed and tested at depths of 1.90m, 2.10m and 2.40m, with the results informing practical recommendations for the final foundation design.
The challenges:
The site presented challenging ground conditions, comprising shallow sand overlying sandstone and microgabbro bedrock across much of the development area. Rockhead was encountered at relatively shallow depths, creating potential difficulties for conventional driven or rammed pile installation. Groundwater was also encountered locally during the investigation.
In addition, laboratory testing identified that much of the site’s natural soils could present an aggressive environment for buried steel elements. Understanding both the structural performance of the piles and the long-term corrosivity of the ground was essential to developing a durable and cost-effective foundation solution.
Results:
The investigation confirmed that pile foundations were a suitable solution for the proposed solar array, although the shallow rock profile indicated that pre-drilling would be required in many areas to facilitate installation. Detailed pile testing demonstrated increasing tensile capacity with greater embedment depth, while compressive performance exceeded the applied test loads across all tested depths.
The assessment also identified areas of potentially aggressive soils, enabling corrosion risks to be addressed during the design stage. Together, the findings provided the client with clear recommendations for foundation design, pile installation and long-term durability of the solar array foundations, helping to de-risk construction and support the successful delivery of the renewable energy project.
