The AngloGold Ashanti Obuasi Mine project is located in the Ashanti region, approx. 320 km north-west of Accra, the capital of Ghana.

AngloGold Ashanti Obuasi Ltd (AGA) Obuasi is commencing Phase 3 of the redevelopment project aimed to provide a robust and efficient infrastructure to support the Obuasi Mine in producing 400 koz per annum from the underground mine; progressively delivering 6000 tpd in a cost-efficient manner for the life of the mine. The New Kwesi Mensah ventilation shaft is to be used for the ventilation of the extension of the Obuasi underground gold mine.

 

BAUER Engineering Ghana was awarded a 6.5 m diameter circular shaft, which was executed with piles with a maximum depth of 30 m. The embedment depth of the piles into the rock was between 0.5 m and 1.0 m.

 

Geology

Lateritic soil was encountered down to 22 m. The observed soil ranged from moist clayey gravel to wet silts and clays. Rock was encountered from 22 m. A 4-m transition zone from soil to rock was moderately weathered. UCS value of fresh rock (greywacke with minor schist) is up to 80 MPa.

 

Scope of works

• Guide wall for the secant pile wall
• 34 nos secant piles Ø 880/780 mm, max 30 m deep for one circular ventilation shaft
• 4 nos load bearing piles Ø 1180/1160 mm, max. 29 m deep to provide solid anchor points for the raise borer beams
• 1 nos drilled at the center of the KMVS shaft position to enable piloting through concrete pile instead of weathered ground, Ø 1180/1060 mm, 29 m deep.

 

 

Miscellaneous

The center pile and support piles were installed using 1180/1060 mm diameter drilling tools. The embedment depth into the rock length was varying depending on the in-situ geological ground conditions. And approx. 20 m of temporary casing were installed during the drilling. The secant pile wall was executed as “hard / hard” pile wall of 30 MPa concrete with sufficient pile overcut to ensure the technical design requirements. In addition, the secondary piles had tobe reinforced full length.

 

INFO

Construction Method:             Secant pile wall

Construction Material:            Concrete, steel

Main Equipment:                    BAUER BG 28

Construction Period:              April 2022 - May 2022