Mill Rig Wind Farm

What was the aim of the work?

Natural Power was asked to implement and report on detailed ground investigations across OnPath Energy’s Mill Rig Wind Farm site based in Central Scotland. The development included three borrow pits, which were used for the extraction of construction aggregates, an electrical sub-station and several met mast locations. The aim of the ground investigation was to provide key information on the geotechnical performance of ground conditions and of existing track infrastructure for the increased loading from delivery of the latest wind turbine components. This information was then used to inform the design of turbine foundations and supporting infrastructure.

What was involved?

The project involved the deployment of several ground investigation services which included:

Rotary core borehole drilling, sampling and detailed logging,

Trial excavation and onsite geotechnical performance testing,

Peatland surveys,

Electrical and seismic refraction geophysical surveys,

Aerial based topographical survey using semi-autonomous drone technology.

What was the outcome?

The team was able to successfully deliver high-quality ground investigation to national standards. As principal contractor, Natural Power was able to complete the works safely and efficiently and ensure the comprehensive and on-time delivery of factual and interpretive geotechnical reports.

What did Natural Power do to get this result?

Natural Power was asked to deliver the ground investigation work to a narrow time schedule which meant that efficiency and safety had to have the highest priorities. The site works were managed by Natural Power’s engineers with all investigation works delivered in-house.

Before starting on site, the team was able to work around and redesign specifications to avoid impacts to sites of special scientific interest (SSSIs) and special protection areas (SPAs) during breeding bird season. By working alongside the clients’ appointed ecological clerk of works (ECoW) they ensured that there was no disturbance to local raptor populations without holding up the work schedule.

Natural Power used its specialist drilling rigs to access the soft ground and forested areas on the site while its multi-disciplinary team was able to form an expert understanding of how the ground conditions impact the construction phase of the project. This was invaluable as the work on site required active felling to gain access to the site investigation locations needed for rotary drilling. Without this they would have been unable to stay on schedule. Further complications arose from a Met Office named storm and numerous windblown trees. However, this failed to impede progress as the team worked safely with the forestry operators to manage the access and felling works.

The geophysical survey team utilised high resolution seismic refraction surveys. This decision was due to the uncertainty in feasibility of one of the borrow pit location. The non-intrusive sub-surface imaging provided rapid high-quality results and, in conjunction with rotary core drilling, it was possible to establish 2D ground model.

The client required a short turnaround for geotechnical reporting to meet pre-construction tender milestones. Natural Power delivered the preliminary report complete with over 400m of drilled, sampled, and logged core, interpreted seismic refraction surveys and hundreds of other investigation data points. Natural Power delivered a true multi-phase ground investigation to the industry standard.

Client Feedback

“We have been carrying out a wide range of tests and surveys on the Mill Rig site since May and are pleased with the results from this.

“Once operational, Mill Rig is a site that will deliver 30 years’ worth of clean energy to homes across the country as well as delivering significant benefits for local communities for many years.

Gordon Thomson, projects director