Derrybrien Windfarm, Co. Galway

Peat Stability

The project involved the construction of 70 turbines with over 20 km of site access tracks, most of which were constructed as floating roads on the peat. All of the turbines were located in areas of blanket bog on an upland site and there was a large peat slide on the site during and early stage of construction.

AGL Consulting were specialist geotechnical consultants to the Contractor to assess peat stability on the site and to monitor the construction of the remaining elements of the work. Our scope of work included the following:

• A forensic investigation into the cause of the slide including detailed walkover surveys, specialist peat sampling and laboratory testing, slope stability analysis and finite element modelling.
• Supplemental specialist investigations across the site involving peat probing, in-situ vane shear testing and peat sampling for the assessment of the floating roads and peat repository sites.
• Stability analysis for all 17.5 k, of the floating roads and peat repository sites with full-scale serviceability and proof load testing.
• Devising and implementing a certification system on site to manage peat stability during construction, which included detailed evaluation and specification of the Contractor’s method statements for road construction, peat excavations and spoil management, with appropriate risk mitigation measures.

All of the remaining work was successfully completed on the site without any further incident. All of the site roads were certified for the design crane loading, and all of the excess peat and mineral spoil from excavations was safely stored on site.