ABSTRACT: It is evident that the reserves available for mining in the goldfields of South Africa are likely to be significantly reduced in 10 to 15 years. A significant percentage of the ore reserves, within gold mines of South Africa, are probably locked up in pillars. Although some of these pillars were especially designed to reduce the closures and energy release rates, other pillars were formed because of increasingly difficult mining conditions, better reserves elsewhere, or an un-pay block at the time of mining. With shrinking reserves at reasonable depth, some of these remnants have to be mined to ensure sustainability and in certain cases preservation. However, such mining is expected to be carried out at higher average stress levels when compared to stress levels for conventional mining panels. As a result the hazards and risk to safety is expected to be higher. The need to develop methodologies to identify the hazards associated with remnant extraction to ensure higher levels of safety and improved efficiency in production, is therefore of paramount importance to all stakeholders. Until now, although there is a considerable amount of remnant extraction, very little research has been done to evaluate the risks involved. This paper reports on some of the findings of a three year research project undertaken to understand and quantify the hazards associated with remnant mining.
INTRODUCTION Although many remnants have been extracted and many are in the process of being extracted, the rockmass behaviour within these remnants is not well understood or documented. Much of the information and most of the designs in use today are based on experience passed on between practitioners.
From an industry survey, Rangasamy and Jager [1] concluded that in the Far West Rand region, a definition for remnants based on size and seismic history is favoured. The shape, block stress and geology are considered secondary definition criteria. In the Klerksdorp and Free State regions, stress, geology and seismic history of the area feature prominently in the definition of remnants.