Modern Mining December 2015

GEOTECHNICAL

risk at Orapa vehicular traffic into and out of the open pit. One of the slopes that required rockfall miti- gation extends over an area of 57 040 m 2 . The linear horizontal length of the area is 320 m, with the average height of the highwall slope being 178 m. The second slope extends over an area of 34 960 m 2 , with a linear horizontal length of 330 m, with the average height in this case being 106 m. Wepex had previous experience of provid- ing viable solutions to rockfall problems at mines, having completed similar projects at Debswana’s Jwaneng mine (a first project in 2010 of 54 000 m 2 and a second in 2013/2014 of 135 000 m 2 ), as well as Anglo American Platinum’s Mogalakwena mine in Limpopo (where the area involved was 40 000 m 2 ). With all three of these projects, Maccaferri’s prod- ucts and Melis & Du Plessis’ innovative design were used, achieving the desired results, with visible, quantifiable success. Rockfall mitigation is not a recent require- ment for open-pit mining activities. Various factors such as natural degradation of the rock mined, insufficient catchment areas, poor min- ing practices and rainfall cause rockfall hazards to develop. There are a number of mitigation options available and all have variable time, cost and quality implications. One of the primary reasons a drapery sys- tem was chosen for Orapa was the height of the highwall slopes that required mitigation which extended to over 180 m above the haul road. The drapery mesh solution that Wepex adopted prevents a significant number of rocks from falling in the first instance or, alterna- tively, in the case of rocks which have become loose, intercepts them, allowing a significant number to work their way to the bottom of the drape wire mesh without impacting the normal operation of the haul road. Many alternative solutions adopt the approach of trying to ‘catch’ the rocks on their way down to the pit floor or haul road. By the time these rocks have reached the catchment devices (or missed them and hit the pit floor or haul road) they have reached a significant velocity! Benefits of the drapery mesh system include minimal to no environmental impact and the fact that the quality and construction of the Maccaferri drape wire mesh product used offers a longevity that exceeds the projected require- ments for mitigation of the areas. The wire mesh chosen for the project needed

Inspecting the integrity of the drapery mesh system.

Two Decoilers specially designed for the project were deployed on the contract.

December 2015  MODERN MINING  23