ABSTRACT:
It is difficult to predict the behaviour and failure of large rock slopes with a high level of confidence. The reasons for this include an incomplete understanding of the uncertainties contained in the geotechnical model used to develop our slope designs and our inability to model precisely the physical process involved in slope failure. The methods we do use to describe the anisotropic strength of a closely jointed rock mass and model its deformation are highly subjective and experiential. Consequently, different operators not infrequently provide quite different results from the same parent data set. These difficulties stress the need for research into the behaviour of closely jointed rock masses in the environment of an open pit. This research work is in hand, but realistically is a medium to long term task. However, techniques that can help us assess our level of uncertainty in the total design process exist now and can be incorporated in a risk management plan from day one of project development. These methods include quantifying and reporting the uncertainties in our geotechnical data base, using this information to quantify the risk levels for different slope configurations, defining acceptable risk levels in terms of safety and economics, and using our slope monitoring systems to formally link these criteria to the capacity of the mining equipment being used at the mine site. We may lack a high level of confidence in the slope design predictions we have made, but most certainly we can establish a risk model that will help us to understand the uncertainties in the design and quantify the effect they will have on the viability of the project.
1 INTRODUCTION
Historically, the largest open pit mines have been from 300m to 500m deep.
