1. Synopsis
This paper will focus on the use of the "wet-mix" Steel Fibre Re-inforced Shotcrete as a permanent lining in deep shafts, accessing gold bearing reef. It will cover all aspects relating to the choice of this material covering the geological conditions through to the final quality control. All procedures are in line with ISO 9001, as JCI projects who manage the project, are an approved company thereof.
2. Introduction to the South Deep Shaft
South Deep, which is a gold mining operation controlled by the Placer Dome Western Areas Joint Venture, is situated about 50km west of Johannesburg and 20 km south of Randfontein in typical Gauteng Highveld country. It is the largest single gold deposit known in the world. The ore-body is complex and dips North/South at + 18 degrees between 2500 m and 3500 m below surface. The thickness of the ore-body varies from 1 m to 90 m and has a planned life of mine in excess of 60 years at 220 000 reef tons per month.
The mine occupies a lease area of approximately 1 481 ha. The northern portion of the mine's lease area comprises a gently northward sloping dolomite plain containing depressions typical of karst type topography. Southward, two prominent ridges separated by a dolomite inlier provided a suitable site for the mines surface shaft (South Shaft) with its associated infrastructure. Kloof, Libanon, Venterspost and Randfontein Estates Gold Mines at its western and northern extremities bound the mine, respectively. The figure below shows the position of the mine relative to surface infrastructure and neighbouring mines.
3. Background to the South Deep Shaft Sinking Project
The South Deep shafts were positioned to pass through the single reef (VCR) orebody for practical, economic and several other advantageous reasons which have been covered in a number of previous papers.
The location necessitated a philosophy of shaft pillar protection. This protection was based on pre-extraction of the reef together with extensive backfilling of the shaft pillar area, prior to the sinking shafts intersecting the VCR reef plane. The practice of shaft pillar pre-extraction is nothing new in the mining industry and is the preferred method of ensuring the long-term stability of a shaft.
The application however, of a suitably designed shotcrete system in an area above and below the pre-extracted reef plane, including an instrumentation monitoring program, is something new to the industry.
This aspect will be covered in some detail in this paper.