South West Scotland Overhead Line Scheme (OHL), Ayrshire

Extensive Ground Investigations support an Overhead Line Scheme (OHL) in Ayrshire, Scotland

To facilitate the connection of renewable generation in South West Scotland and to cater for future load growth, a new network of three 132kV overhead lines are proposed for construction in Southwest Ayrshire.

CGL was appointed to undertake an intrusive ground investigation at each of the 233 transmission tower locations. The ground investigations comprised combined percussive and rotary drilling techniques along with trial pitting. In addition, groundwater monitoring wells were also installed at selected tower locations.

CGL co-ordinated the ground investigations along the routes alongside the principal contractor, Amec Foster Wheeler. To assist with the client’s programme, CGL managed up to three rigs operating on site at the same time.

The proposed OHL routes pass through 56km of either forested land used for evergreen plantations or areas of rugged open sheep farming hillside. This led to difficult access and working conditions during site works, often involving steep slopes, peat bogs, ground laden with tree stumps and inclement weather.

The investigations frequently involved working in remote locations with low ground bearing tracked plant, particularly for an 18 tower stretch across four kilometres of forestry and peat bogs/open hillside. Extra measures were also required as this area is within the environmentally sensitive Afton Reservoir Catchment Area where strict environmental restrictions are in place.

Upon completion of the investigation for each route, CGL provided a Ground Investigation Factual Report which included the exploratory hole logs, core photographs and geotechnical laboratory results.