Lowwall and Ex-pit Waste Dump Slope Design Optimisation Study: Millennium Mine Bowen Basin Queensland, Australia

Slope stability is a major issue in all open cut mines particularly sedimentary operations such as coal mines. The issue of slope stability can have major ramifications on mine safety and eco-nomics and in some instances can cause mass sterilisation of reserves and even mine closures not to mention mine worker casualties. This thesis will analyse the risks and propose design cri-teria for the construction of a significant Ex-pit waste dump behind the Pit C Lowwall at Millen-nium Open Cut Mine. A structurally complex metallurgical coal mine situated along the New Chum thrust fault in Central Queensland Australia. The New Chum Thrust is a significant reverse thrust with 250m of vertical displacement. The resulting highly faulted nature of the adjacent stratigraphy exemplifies the variance of rock masses between each fault block within the re-source area. The difficulty in determining the acceptable slope angle is related to geological variances within different rock masses. In determining the safe maximum slope angle of the Lowwall and Ex-pit waste dump design a series of geotechnical investigations, rock mechanics testing and numeri-cal simulations are used to determine design parameters and models for input into GALENA a limit equilibrium slope stability analysis software. These include but are not limited to down-hole acoustic scanner and highwall mapping analysis, point load and uniaxial compressive tests, Hoek-Brown and STEPSIM4 rock mass strength determination. It was also necessary to develop an accurate geological model to determine the projected bedding dip and different rock mass thicknesses under the proposed Ex-pit waste dump. The Rosenblueth Method was adopted as the risk assessment process for the suit of GALENA limit equilibrium models. A sensitivity analysis of the resulting factor of safety associated with physical and material properties was conducted to determine which rock masses are more likely to result in a poor factor of safety and potential slope failure. The results of this sensitivity analysis provided the identification of the three rock masses to be varied as part of the Rosen-blueth Method and which physical parameters require the greatest ongoing monitoring atten-tion. Resulting data and analyses while presented as an isolated case study can be observed as an example of the methodology for other open cut sedimentary operations