TECHNICAL | DRILL & BLAST - COIRE GLAS PROJECT
Right:
Epiroc Boomer S2 in action PHOTO CREDIT: JOHN ZAMMIT
Below both images:
Photo of exposed geology and corresponding face mapping sketch at Advance 284 of the Adit PHOTO CREDIT: ANTONIA DECMAN
was also a detailed LiDAR and photogrammetry record of each advance, which provides an unaltered record of the exposed ground, regardless of the support later installed. Forward probing was maintained ahead of the tunnel face, to give early warning of any weak zones, or more importantly, water ingress. A pre- excavation grouting rig was on hand in case of any severe water strikes, but thankfully never used. The Epiroc jumbo in use also provided ‘measure while
drilling’ (MWD) data for every probe hole, blast hole and rock bolt drilled, which when collated, formed a very visual representation of the geological conditions. Tunnelling continued steadily through to November
2023, clocking to reach beyond Ch 700m, almost into the final stretch to the drilling gallery. It was at this point that a feature was encountered consisting of very poor, highly deformed rocks, with ground conditions that fell outwith the existing support classes. By the next advance this feature was present in
almost half the face, and was evidently much poorer ground than accounted for at this depth. In the hope this was a finite feature, an additional short advance was undertaken, but the poor rock continued up to the crown yet again. Additional support was instructed in this area, and tunnelling brought to a safe stop. Sean explained how SSE tackled the issue on all
fronts, and was keen to highlight this period being noteworthy for the collaboration between all of the teams on site. Given tunnelling was on hold, waiting for detailed
GI before starting the design wasn’t an option. From the information available and numerical modelling, Stantec-Cowi proceeded with conservative lining design for the location, the assumptions for which could be verified later on. This design, which became
14 | February 2026
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