The mine is located along the Sefwi Volcanic Belt, a north-east-southwest trending volcanic belt in Ghana. The mine is in the Ahafo region, approximately 307 km northwest from the national capital Accra.
Bauer was commissioned to construct the guide walls and subsequently install three shafts.
These ranged in diameter from 4.1 to 5.1 m. Two of the shafts were intended for the ventilation (Return Air Raise and Fresh Air Raise) and one for waste extraction for the Subika underground mine extension.
Overburden soil in the upper 31 m followed by hard Gabbro rock with a strength up to 293 MPa.
Scope of Works:
- Guide walls
- RAR shaft: 29 nos 1,180/1,060 mm Ø piles
- Waste Pass shaft: 25 nos 1,180/1,060 mm Ø piles
- FAR shaft: 24 nos 1,180/1,060 mm Ø piles
The piles had to have a rock socket of between 1.0 and 2.0 m to ensure the piles were embedded in the solid rock and not the weathered rock.
For RAR shaft having a diameter of 5.1 m, 24 secant wall piles, 4 bearing piles and 1 centre pile were installed. The maximum depth reached here was 21 m. On waste pass shaft, for recovering mine waste, ﬁbre reinforced concrete plus standard reinforcement was used with a 45 MPa concrete to enable a higher abrasion resistance of the piles once the shaft was completed. The maximum depth of the 25 piles (20 secant wall piles, 4 bearing piles, 1 centre pile) reached 18 m. For RAR shaft, the diameter was 5.2 m. The 29 piles (24 secant wall piles, 4 bearing piles, 1 centre pile) installed reached a maximum depth of 31 m.
Construction Method: Secant pile wall
Construction Materials: Concrete, steel
Main Equipment: BAUER BG 28
Construction Period: August 2020 - February 2021