The Large Open Pit (LOP) project is an international industry-sponsored research and technology transfer project focused on the stability of large slopes associated with open pit mines, developed and managed by Dr John Read of the Commonwealth Scientific and Industrial Research Organisation (CSIRO Earth Science and Resource Engineering, Brisbane, Australia) in April 2005. Planning for the LOP Project commenced early in 2004 when a scoping document outlining a draft research plan was submitted to a number of potential Sponsors for appraisal. An inaugural Project Sponsor’s meeting was then held in Santiago, Chile, on 22 August 2004, when the proposal was examined in detail by mining company representatives and a number of senior practitioners from across the mining industry. There was a strong positive response to the proposal, which resulted in the participants agreeing to convene an interim management committee to overview and help finalise the direction of the research plan. Since then, its ultimate goal has been to deliver a better understanding of the mechanisms of slope failure and new tools for the slope design practitioner, including:
- A new generation of pit slope design guidelines directed at topics including the fundamentals of slope design, field and laboratory data acquisition, rock mass characterisation, preparing the geotechnical model, assessing and reporting data uncertainty, slope design acceptance criteria, performance assessment and slope monitoring techniques, controlled blasting, risk management, and open pit closure.
- Rock mass strength determination using a Synthetic Rock Mass Model (SRM) that uses intact rock strength and jointing data to construct an “equivalent material” envelope that honours the strength of the intact rock and joint fabric within the rock bridges that may occur along a candidate failure surface in a closely jointed rock mass. Importantly, the SRM model can be applied to different sample sizes, making it possible for the first time ever to demonstrate the effect of scale and defect orientation on the strength of the rock mass.
- Fully coupled modelling of transient flow within a closely jointed rock mass environment, including variation in pore pressures as the slope is excavated.
- 3D structural modelling and slope failure analysis tools, including a modified PFC3D procedure based on lattice mechanics that incorporates the SRM concept and coupled flow deformation behaviour which will run 10 times faster and handle larger models than the current PFC3D or equivalent simulations, thus enabling direct modelling of significant portions of a real slope.
- Managing the risks presented by open pit mine slopes such that optimum value to mining businesses can be achieved.
Research Themes
Geotechnical investigations are an integral part of large open pit mine development. They routinely follow an orderly path of data gathering aimed at providing as much information as possible about the engineering characteristics of the ore body, especially the lithology, structure, mineralisation, alteration, weathering, and hydrogeology. This information is usually augmented by laboratory tests to determine the shear strength characteristics of the rock mass and frequently is encapsulated within one of a number of alternative rock mass classification schemes specifically adapted for use in rock slope engineering. It may also be displayed in one of the several three-dimensional mine planning visualisation systems that are now available in the marketplace. Ultimately, the assembled information is used in limiting equilibrium and numerical stability analyses that, in parallel with cost-benefit and risk analyses, are aimed at predicting the optimum wall design. The final part of the package is likely to include recommendations for monitoring pit wall performance, rainfall, and groundwater during mining.
The need for and acceptance of this investigation, design and monitoring process as routine has been underpinned by all manner of examples demonstrating that ground stability and wall slope design are fundamental variables in the economics of operating large open pit mines. Managing risk is also a key performance requirement. The end goal is achieving reliably engineered mine slopes that, if they fail, do not cause loss of life, equipment damage, sustained losses of production, or the inability to achieve published reserves.
Depending on the scale of the investment there will, however, be trade-offs between the intensity of the investigation, the design work performed, and the perceived criticality of the slope design. When planning, the leading questions are nearly always concerned with “when is enough enough?” The more important but less often asked question is, “do we understand the design and can we quantify its reliability?”
When answering these questions critical gaps in our knowledge and understanding of the relationships between the strength and deformability of rock masses and the likely mechanisms of failure of rock slopes in large open pits are inevitably exposed. There is also a highly diverse literature that outlines any number of ideas concerning likely failure mechanisms and a plethora of suggestions of how best to analyse them for stability. A frequent outcome is a confusion. Many slope design practitioners are thus faced with an uncertain choice concerning which design approach and which method of analysis will give them the best outcome.
The purpose or theme of the Rock Slope Stability Project is, therefore, to address these critical gaps and uncertainties in our knowledge and create more effective ways than now exist for predicting the reliability of rock slopes in large open pit mines.
From 2005 to July 2014
The LOP project was funded by the following mining companies, representing a majority of the world’s diamond and base metals production, including:
- Anglo American plc, London, United Kingdom
- Anglo Gold Ashanti Limited, Johannesburg, South Africa
- Barrick Gold Corporation Pty Limited, Toronto, Canada
- BHP Billiton Innovation Pty Limited, Melbourne, Australia
- Compañía Minera Doña Inés de Collahuasi SCM, Iquique, Chile
- Corporacion Naciónal Del Cobre De Chile (“Codelco”), Santiago, Chile
- DeBeers Group Services, Johannesburg, South Africa
- Debswana Diamond Co., Gaborone, Botswana
- Newcrest Mining Limited, Melbourne, Australia
- Newmont Australia Limited, Perth, Australia
- Ok Tedi Mining Limited, QLD, Australia
- Technological Resources Pty Ltd (the “Rio Tinto” group), Australia
- Teck Resources Limited
- Vale, Rio de Janeiro, Brazil
- Xstrata Queensland Limited, Brisbane, Australia
CSIRO Exploration & Mining was the lead research group, responsible for managing the research and coordinating the efforts of the participating research partners and industry practitioners. Given its many successes, among which was the publication of what is probably the most widely used reference on open pit slope design, there was a strong desire by the sponsors to continue the project but in a format that would reflect current industry needs.
Mid-2016 to mid-2019
The project vision was developed by a committee of sponsor representatives and endorsed by the remainder of project sponsors. The project was therefore renewed under the leadership of Dr Marc Ruest form the University of Queensland (UQ) as LOP II in June 2016. After Dr Ruest departing UQ in mid-2017, the ongoing management of the LOP II Project was transferred to Professor David Williams and Dr Mehdi Serati from UQ with 8 sponsors including:
- Anglo Gold Ashanti, Johannesburg, South Africa
- Barrick Gold Corporation Pty Limited, Toronto, Canada
- BHP Billiton, Brisbane, Australia
- DeBeers Group Services, Johannesburg, South Africa
- Debswana Diamond Co., Gaborone, Botswana
- Newcrest Mining Limited, Melbourne, Australia
- Rio Tinto, Brisbane, Australia
- Vale, Rio de Janeiro, Brazil
The LOP II runs for 3 years from June 2016 to June 2019.