Rock slope design at great depth as open pit mining progresses beyond the available experience base: expected behaviour and potentially robust design approaches

摘要

Open-pit mines are progressively exploiting minerals at great depth and beyond the availableexperience base. In-depth and well-considered research is crucial if mine planners anddesigners are to understand the behaviour expected at these new depths. Approaches thatappear to offer the potential for robust design and analysis of rock slopes in the future undersuch conditions need to be thoroughly investigated. This paper discusses several aspects thatneed to be considered in order to come up with a robust slope design methodology at greatdepths as open-pit mining go beyond available experience base.An open-pit mine thrives on an appropriate slope design and slope stability analysismethodology. A balanced trade-off between risk and economic benefits has to be struck if asuccessful operation is to be achieved. A slope has to be steep enough to allow a minimumstripping ratio, while at the same time it has to be gentle enough in order to minimize risk offailure.The critical review in this study establishes that there are behaviours unique to deep openpitmining. As depth increases, the rock mass suffers severe strain extension effects, multiplefailure mechanisms are possible, complex geological and groundwater conditions areencountered, and the risk of slope instability increases. In consideration of different state-ofthe-art approaches to rock slope design, the author proposes several different approaches torock slope design that can be used to tackle these challenges. The most promising approacheshave applied the concepts of discrete fracture network (DFN), synthetic rock mass (SRM),simulation of mining process, modelling of progressive failure, and 3D and probabilisticanalysis. Powerful numerical modelling tools for slope design and analyses such as ELFENand Slope Model have also been developed for use at great depth.For the successful implementation of these approaches the author strongly advocates thatthey need to be reinforced with sound slope management strategies such as monitoring,groundwater control, and smooth blasting. Slope design and analysis at great depth alsorequires in-depth consideration of Bieniawski's design process and principles, a dependablecode of practice (COP), and sound geotechnical data collection and database management.In addition, the numerical models built for the slope design need to take Starfield andCundall's guidelines for numerical modelling into consideration.