DRILL & BLAST - COIRE GLAS PROJECT | TECHNICAL


but as it would become clear, Coire Glas was a model of collaboration, and all the key players in the venture were represented. The night was an honest retelling of the full story of a


project, from inception to completion, although in this case it’s only the first chapter in what will be the biggest scope in underground works of its kind in the UK in a generation. The presentation kicked off with an overview of


the full Coire Glas scheme, an ambitious pumped storage hydroelectric power station, capable of up to 1,300 MW generation, and 30 GWh’s long duration storage. Sean Murchie, Engineering Geologist for the project developer, SSE Renewables, started off by taking us through the landscape of this part of the Great Glen, with the plant’s lower works on the banks of Loch Lochy, and the upper reservoir located in a convenient horseshoe of the Munro ‘Sron na Coire Garbh’. In between the two, sits Sean Mheall, the Southern ridge of the Munro, and it is inside of this mountain that the workings of Coire Glas will be situated: turbines; pumps; watercourses; surge shafts; and, kilometres more of access tunnels. The concept of the Exploratory Works came


from SSE’s commitment to obtain detailed Ground Investigation (GI), to de-risk their future works, especially given the size and scale of the planned excavations. It was stressed that although the broader Great Glen has been studied extensively, relatively little site specific information was available and this was identified as a project risk early on. Those that are aware of the geological history of


the Great Glen, the longest fault line in the UK, will understand that it was likely to be an interesting study. The published geology for the site included two main domains: the Great Glen Fault Zone itself, including heavily sheared and brecciated fault rocks, these cataclastic rocks having a predominantly quartzite or psammite protolith, with subsidiary amounts of semipelite, amphibolite and metacarbonate; then, to the North, the Tarvie Psammite Formation, consisting of more competent meta-sediments - predominantly psammite (metamorphosed sandstone) with subordinate bands of semipelite and/or pelite. Sean continued with a rundown of SSE’s strategy


for the Exploratory Works, involving a two pronged approach: a campaign by Fugro of conventional surface GI (in some unconventional locations, such as a borehole from the top of the mountain and others from the floor of the coire (glacial hollow); and, the underground works by Strabag, accessing areas that surface drilling simply couldn’t reach. This would be made possible with the construction of the Exploratory Adit - a relatively small heading, originally planned at 900m in length, and then to be followed by a campaign of underground GI, to target the locations of key structures even deeper underground. The design for the Exploratory Adit had to be


undertaken with only the geological information already available, supplemented by some limited surface outcrops, and a healthy amount of engineering


February 2026 | 11


judgement. Tom Taplin, Engineering Geologist in the design joint venture of Stantec-Cowi, the client’s Designer, explained how the factors at play were run through the Q-system, taking into account rock quality, jointing, and stress influences, for a range of anticipated conditions. This analysis resulted in a suite of conservative designs, or support classes, from A to D, that could be installed depending on the actual conditions encountered underground. For areas of better ground, like Class-A/B, ground


support consisted of a thin sprayed concrete lining (SCL), with either spot bolting, or systematic bolting respectively. If conditions deteriorated, Class-C support included lattice girders and overhead spiling. Class-D


Loch Lochy and the Coire Glas Exploratory Adit, aerial drone photo


PHOTO CREDIT: IAIN MURCH


Below:


Published geology of Coire Glas site


(annotated BGS area map)


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