High Speed Shaft Sinking Techniques In South Africa

1. INTRODUCTION The economic importance of bringing a new mine to production in the shortest possible time, is well known. In recent years the rate of escalation of mining costs has accelerated more rapidly than at any time in the past. This fact has enhanced the need to reduce time schedules and made it an overriding and predominant objective when planning new shafts. The squeezed profit margins and widely fluctuating metal prices have also increased the emphasis being placed on this aspect. Moreover the increase in the present value of future profits due to the reduction in the time element, can be so substantial that expenditure on equipment and additional labour can be justified conditional on sufficient gain in shaft sinking speed being achieved. The emphasis on time saving becomes more abundantly clear when considering the very large increase in the capital required to bring a modern underground mine to production. As an example, the initial capital expenditure requirements for a large new gold mine in the Western Transvaal, which has commenced production recently, is estimated at R200M, and a major extension to another deep level mine in the same area is estimated at R300M. With the uncertainty of future metal prices and the recent trends in increasing inflation, it is becoming more difficult than ever to estimate the profitability of proposed mining projects and any cost saving due to more rapid sinking of shafts can only assist in this respect. Since the shaft systems are frequently the most expensive set of underground excavations and no other underground work can commence until they are completed, the speed of shaft sinking is subject to closer scrutiny than in the past. In the following sections of this paper the factors contributing to the high average advance rates achieved by South African shaft sinkers are discussed. It is difficult, if not impossible, to estimate the effect of any single factor, in isolation, on the overall sinking achievements. However, the cumulative effect of improvements made in the inter-related activities is, probably, the most important contributor. Although there has not been any single major technical change or innovation to shaft sinking practices in the last decade, the average sinking speeds have increased, due to improved application and technical improvements in established procedures. 2. GENERAL When discussing South African shaft sinking techniques and average sinking rates compared to those achieved in other parts of the world, it should be remembered that the size and depth of South African shafts are often considerably greater than in most other countries. Typical examples of shafts either in the course of sinking or recently completed are -