Investigating the effectiveness of a ground support system implemented on Block A: A case study of Southern Africa Metalliferous Mine

Abstract

This study aims to investigate the effectiveness of the ground support systems that are planned to be implemented on Block A, which will be excavated through the Marikana fault zone. The block of ground being prepared for mining has been physically affected by the presence of the Marikana fault and is therefore geomechanically and geotechnically weaker than the normal stoping conditions on the rest of the shaft. Data collected during the raiselines mapping was used as input into the numerical modelling software (Dips and JBlock), which indicated a major scatter of joint orientations in Block A. Shallow dipping orientations of 276 /14 , 174 /11 and 69 /14 were observed. An average RMR below 50 was calculated from the field mapping data which indicates that the quality of the rockmass in Block A is relatively poor and pose the risk of rock falls due to high probability of unstable rocks. Jblock simulations were performed to estimate the load bearing capacity of the roof bolts. The simulation results showed that the probability of failure reduced to 26% at a loading capacity of 160 kN as opposed to a 60% probability using 100 kN capacity. Likewise, the probability of block failure for 1 m blocks and the maximum support failure decreased to 27% and 5% respectively. The area simulated is a stoping panel with a 15 m face length and a 30 m back length. A total number of 10 000 keyblocks were generated and the probability of failure was highest for 1 m at a 60% in between support. The JBlock analysis shows that the support spacing implemented at Mine A does not sufficiently account for all rockfalls that can occur due to keyblock formation in the hangingwall. In order to effectively support the unstable ground, it is recommended that longer grouted coupling roof bolts of 2 m length spaced at 1 £ 1.2 m should be installed, as opposed to the current mechanical end-anchors (ungrouted) of 1.6 m length spaced at 1.5 m £ 1.5 m.