Phillip Jones Reference No. G-01483.84-008-LR-Rev0_FINAL OceanaGold Corporation 17 June 2022 3 Option 1: Prefabricated structural cover This option involves a metal plate (steel, aluminium, stainless steel or equivalent) being installed over the shaft opening and bolted to the existing concrete shaft lining and supported on the steel cross beams. The plate is then covered by a structural steel frame and Glass Reinforced Plastic (GRP) or equivalent. The purpose of the structural frame and cover is to protect the plate from the elements while allowing for periodic condition inspections. The structural steel frame and plate will be prefabricated in sections that can be transported to the shaft opening by helicopter for assembly. The structural steel frame would require anchoring into the concrete ring beam; or would require a concrete footing to allow for the surrounding ground conditions. The structural steel frame would be covered in GRP. GRP has low weight with high mechanical strengths, resistance against chemical corrosion, UV radiation and temperature extremes. GRP is also waterproof, fire-retardant, and highly durable material with a long-life expectancy. The ground level around the outside of the shaft lining would need to be built up to the height of the shaft cap above ground level at a suitable angle to allow surface water to flow away from the shaft opening. A sketch of this design option as a plan and section is presented in sketches 3 and 4 with details A and B in Attachment B. Option 2: Reinforced cast in-situ concrete cover This option involves installing a reinforced concrete cover over the shaft opening and bolting the cover into the surrounding ring beam and steel crossbeams. The reinforced concrete cover has a nominal thickness of 450 mm. The opening of the shaft would need to be covered by a temporary element that supports a working platform and false floor on which the reinforcing can be assembled and the concrete can be placed. Concrete, batched offsite, will need to be transported by helicopter to the site. Based on a 5.5 m diameter shaft opening, the volume of concrete required will be 10.7 m3. The ground level around the outside of the shaft lining would need to be built up to the height of the shaft cap above ground level at a suitable angle to allow surface water to flow away from the shaft opening. A sketch of this design option as a plan and section is presented in sketches 5 and 6 in Attachment B. Option 3: Cemented backfilling This option involves placement of cemented backfill in the shaft opening in multiple lifts. The backfill would be a self-consolidating type concrete. The backfill would be mixed underground and pumped into the shaft via boreholes drilled into the shaft at multiple elevations, or pipe to be suspended in the shaft and terminating at multiple elevations. A specialized concrete pump capable of pumping the cemented backfill would be required. Such pumps are sometimes referred to as “high-rise” concrete pumps as they are used in the construction of high-rise buildings in civil construction. Prior to selecting this option, additional studies are required to confirm the
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