2019-05-17_REVISION - M1994117 - Laserfiche WebLink

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Seepa e Failure Condition Head(ft) Pressure(psi) Pressure Gradient(psilft) Factor of Safety Operation 4.5 1.9 0.6 16.6 Current 15.2 6.6 2.2 4.5 Design 17.6 7.6 2.5 3.9 Max OP 22.1 9.6 3.2 3.1 Maximum 102.6 45 15 0.7 The limitation of the West Driefontein Mine seepage experiment and calculations is that they only consider leakage through the bulkhead, concrete-rock contact, and immediate rock mass. They do not consider seepage or piping through joints or shears parallel to the tunnel, across the plug. The Times Mine Bulkhead is located on a vein that was not pressure grouted. Under high head, this is the most likely seepage path. CONCLUSIONS ■ The Times Mine Bulkhead is currently holding back a head of 15.2 feet of water(6.6 psi). The stated design capacity is 17.6 feet (7.6 psi). ■ The water may have been pumped into the mine in the past or groundwater may be seeping in and raising the mine pool. ■ The maximum head possible behind the bulkhead, when water overflows through the Wynona Shaft well casing, is 102.6 feet (45 psi) ■ Based on our calculations, the bulkhead should perform adequately under the design, current and proposed operational conditions. ■ Under the maximum proposed operational conditions, the bulkhead area should be observed and conditions documented on a regular basis with a particular focus on any increases in seepage or the development of any concentrated areas of flow. Should a significant flow or seepage increase be observed, the mine pool would need to be lowered rapidly. ■ Based on our calculations, the bulkhead would most likely fail under the maximum loading condition where water overflows at the Wynona Shaft. The likely failure mode would be excessive seepage and water flow past the bulkhead, possibly through the vein in the back. ■ The total volume of water stored at or above the elevation of the bulkhead is unknown. If the Wynona 100 Level is lower than the bulkhead, the additional volume from the Wynona Shaft is negligible and water behind the bulkhead is limited to the Times Mine volume of approximately 25,000 cubic feet (187,000 gallons). If the Wynona 100 Level is higher than the bulkhead, most of its unknown volume would be stored behind the bulkhead(i.e. it would drain out if the bulkhead was opened). ■ Minor seepage is visible along the contact between the bulkhead and the rock. The seepage continues 3 feet past the air side face. ■ The presence of oxidized iron precipitate on the bulkhead face, rock interface and vein suggest mine pool water is seeping around the bulkhead. This is typical. ■ Total flow past the bulkhead is negligible. No concentrated flows were observed. ■ The bulkhead appears to be performing adequately. There are no visible signs of distress. - 6 -