Error reduction in slope stability assessment

1. Introduction Slopes in quarries and open pit mines, as well as all the types of embankments (stockpiles, tailing dams, waste dumps) resulting from mining and mineral processing activities, must be considered as "geotechnical structures". Therefore, the design and implementation of these structures must be conducted with all consideration. Considering an economical plan, the selection of reasonable slope angle for excavations in open pits is crucial as it affects the stripping ratio (ratio between waste and ore tonnages) and/or the tonnage of recoverable ore with consequences on the benefits or return on investment of the mining operations. In terms of safety, various disasters can be mentioned (e.g. Failure of the waste dump at Aberfan in Wales in 1966, many failures in tailing dams on every continent or failure in open pit mines and quarries) in which safety and profitability of the mining operations were often adversely affected by various slope instabilities. Finally and with respect to environmental issues, long-term stability of slopes in quarries, open pit mines and mainly embankments must be maintained, at the end of operations and even after that. So, slope design is the process of determining the optimum slope angle for input into pit design, that is to say the slope angle at which the net benefit is the highest. Mining at flatter angle will result in higher stripping costs and reduced ore recovery. Conversely, mining at steeper angle would result in slope instability costs higher than the increased ore recovery. The Earth and Mechanical Sciences are the primary focus of this issue, in particular, disciplines such as: engineering geology, geotechnical engineering, soil mechanics and rock mechanics, hydrogeology and underground water. The main aim of this section is to highlight the basic principles of the slope design process. Though, these principals can be well presented and understood, however it is not enough and it is always necessary to involve slope stability experts; More advanced and sophisticated scientific methods can be only applied by an expert; they have access to laboratory facilities; they have long-time experiences on field studies so they have better understanding of each project uniqueness; considering above, experts can provide more comprehensive definition of the problem and consequently more reliable designs. It is again necessary to emphasize that each case study is always a new special and unique case. This section also presents different cases of difficulties encountered in open pit slope design.