Backfill

The principal support regime on the Merensky reef is the placing of backfilled bags at intervals of 1.5m. Backfill is placed in 65% of the mined out Merensky reef areas. Between 60% and 70% of all panels are being backfilled concurrently with the advancing faces, thereby enhancing both local and regional stability.

In the UG2 area backfill accounts for up to 30% and is used in conjunction with stabilising pillars. Backfill provides a valuable means of regional support and also serves to control ventilation in working areas and reduces the transmission of heat from the surrounding rock.

The backfill (waste) is supplied from the surface metallurgical plant backfill silo in a slurry form. It is pumped to the shaft and gravity fed through 70/114mm diameter pipelines to the stope horizon. The slimes are pumped tightly into porous 'backfill bags' that retain the +45 micron sediments, yet release the water, to leave a noncompressible, rigid structure to resist and contain roof lowering.

The backfill bulkhead and paddock design were recently re-evaluated and found to be technically sound. Backfill quality and installation is strictly controlled. A specialized backfill contractor, Concor, is employed to undertake and monitor the backfill placement underground.

More on underground support systems.