Stability assessment and slope design at Sandsloot open pit, South Africa

Sandsloot open pit is located on the northern limb of the Bushveld Igneous Complex. II is the largest open pit platinum mine in the world. Three major joint sets have been recognized at Sandsloot, which are related to the reg ional tectonic history. They have an important influence on slope stability in the open pit, notably in terms of planar and wedge failures. Detailed g eological and geotechnical data are often a notable unknown factor in the d esign and operation of an open pit, the lack of which may pose a significan t risk to the mining venture. As data are accumulated and used effectively, so the risk of unforeseen conditions is reduced, and accordingly safety an d productivity is increased. Usually, the geotechnical work undertaken at a n open pit mine is in connection with improving slope stability. At Sandslo ot open pit geological and geotechnical data have been obtained by face map ping, scanline surveys, from exploration drillholes and from laboratory tes ts. Such data have been used to delineate different geotechnical zones in w hich different types of slope failure have occurred. These are the usual ty pes of slope failure associated with rock masses, namely, planar, wedge, to ppling and circular failures. Analysis of the data has allowed optimum desi gn parameters to be developed for these zones which has led to improved slo pe stability. In other words, this has allowed slope management programmes to be initiated, as well as slope optimization of the hangingwall. The latt er resulted in an improved slope configuration and an increase in the ultim ate angle of the wall by 7 degrees. This has resulted in substantial saving s, as well as an improvement in safety. (C) 2001 Elsevier Science Ltd. All rights reserved.