A Review of the Stope Support System at Impala Bafokeng North Shaft Owing to Stope Closure at Shallow Mining Depths

Abstract

Impala Bafokeng’s North Shaft is a shallow platinum mine on the western limb of the Bushveld Igneous Complex. Shallow mines experience very little horizontal stress which leads to a support issue of the tensile zone. North Shaft relies heavily on mine pole support due to the requirements for a stiff support system. Elongate support failure in the deeper parts of the mine have occurred due to a change in the loading environment. The support failure has resulted in inadequate support resistance in the back areas and some large falls of ground. In this research report the Hybrid Section stope closure rate was measured. The closure does not appear to be linked to a detachment of a hangingwall parting. The ground penetrating radar scans and borehole data correlate with the observations. The falls of ground are structure related and occur in the back areas of the panel after the elongate support had failed. The footwall material is weaker than the hangingwall material and the pillar punches into the footwall. The footwall fractures and tensile cracks in the panel footwall indicate that the stresses are forced to move horizontally due to the footwall 4 parting plane. The footwall thrusts into the panel causing the high closure observed. The combination of a shorter panel length and pencil sticks would provide adequate support for the high closure rates observed.