A Combined DFN-LE Approach to Improve Inter-Ramp Design


The fundamental technology applied to Inter-ramp analysis for slope design and optimization has not changed significantly over the past decade or two, yet it remains the component of open pit slope performance in which uncertainty is most evident. A number of existing methods are commonly used for inter-ramp slope design, from simple kinematic analysis to advanced three-dimensional (3D) discontinuum analysis. Whilst all of these methods are useful tools in slope design, each has specific limitations. Simple preliminary approaches are quick but fail to consider complex non-daylighting failure mechanisms and the explicit contribution of rock bridges to improving shear strength of sliding surfaces. More sophisticated tools have the capacity for studying complex failure mechanisms but are computationally expensive and require significant development time, particularly when a high number of sensitivity analyses are required. Increasingly, there is a need for an approach that can consider complex failure mechanisms involving both discontinuity and rock mass that is more grounded in a structural geological reality than simple kinematics. In addition, this method must be efficient enough so that a wide range of slope inter-ramp angles (IRAs) and orientations can be evaluated in a practical duration while permitting probabilistic assessments for each configuration.

Golder has recently developed and applied an inter-ramp slope analysis method that addresses these issues by coupling the structural validity of a Discrete Fracture Network (DFN) approach with a 3D stress-based limit equilibrium (LE) assessment of stability, as documented in Valerio et al. (2020), Lawrence et al (2020). To further establish the robustness and widespread applicability of this approach, however, application / back analyses to a number of existing pit slopes where historical instabilities have been observed is required. Scenarios where instabilities were not predicted and/or more complex than initially believed are preferred so that the tool can be rigorously evaluated against an agreed upon suitable design acceptance criteria (DAC).