Predicting the expected time of slope collapse is an important aspect of managing open pit slope stability as it determines the appropriate actions to be taken. It is important to know when to evacuate but is also useful to know well in advance if a particular slope is creeping towards collapse or whether the deformations measured are unlikely to result in collapse. Having this type of information well in advance allows a mine to plan and execute remedial actions, such as schedule changes, slope angle changes and buttresses, that will mitigate economic as well as safety risks. While several methods of analysing slope monitoring data have been published to date, none have been able to establish themselves as the definite answer to any of these questions. This paper evaluates several previously published methods of predicting the time of slope collapse based on the monitoring data collected for slope instabilities that occurred at two of Rio Tinto's Pilbara Iron Ore operations in 2009 and 2010. The methods tested against the data are: CUSUM, inverse velocity and the slope of velocity and time multiplied velocity (SLO) method (Mufundirwa and Fujii, 2008). The paper concludes by evaluating the effectiveness of each of these methods to serve as early warning of impending failure and to predict the onset of collapse. Both instabilities were managed without injury to personnel and no loss of equipment. Predicting the expected time of slope collapse is an important aspect of managing open pit slope stability as it determines the appropriate actions to be taken. It is important to know when to evacuate but is also useful to know well in advance if a particular slope is creeping towards collapse or whether the deformations measured are unlikely to result in collapse. Having this type of information well in advance allows a mine to plan and execute remedial actions, such as unloading of slopes or building of buttresses, that will mitigate economic as well as safety risks. While several methods of analysing slope monitoring data have been published to date, none have been able to establish themselves as the definite answer to any of these questions. This paper evaluates several previously published methods of analysing slope deformation data against two slope instabilities that occurred in the Pilbara. The two slope instabilities occurred at Tom Price's North Deposit (NTD) in 2009 and West Angelas' Centre Pit North (CEPN) in 2010. Both of these slope collapses were managed without harm to personnel or equipment. The basic failure mechanism for both NTD and CEPN was very similar in that failure occurred on a bedding parallel shale band with stability maintained by several metres of Banded Iron Stone (BIF) preventing the shale band from day lighting. In each case the slope instability was triggered by a reduction in the thickness and quality of the BIF buttress. https://papers.acg.uwa.edu.au/p/1308_74_Venter/ An evaluation of the CUSUM and inverse velocity methods of failure prediction based on J. Venter et al. two open pit in...

Investor confidence is largely driven by a mining company's ability to deliver on the guaranteed return on investment. Thus, robust due diligence processes, functioning as part of a mining company's corporate governance, become essential tools to identify hazards that can impact production, assess the associated risks and introduce controls to manage the risks. The geotechnical practitioner is tasked to manage one of the biggest risks on the mine; that of a rock mass instability. Since an instability, or collapse, need not be large to have a significant impact on production, the challenge is to develop an optimised life-of-mine design with a risk management plan that suits the risk requirements of the mining company and investors, whilst meeting acceptable, minimum safety standards. The concept of a Geotechnical Review Board has been adopted in the industry as a vehicle to provide assurance that the geotechnical risks on a mine have been identified and are being properly managed. The review relies on external parties providing appraisals of the design and processes, and experienced oversight of the active operations. In general, these reviews tend to have a unique style; often a combination of the current, visible, critical issues on the mine and issues deemed as important by either the reviewer or a third party. Coupled with the challenge of fluidity in modern planning environments, the geotechnical practitioner is often still faced with uncertainty in the level of geotechnical risk associated with any given mine plan. This paper introduces a geotechnical risk assessment tool that has been developed for use as a leading indicator within AngloGold Ashanti's international operations. The authors aim to provide the reader with insight into how the tool can be utilised to understand a mine's ability to proactively identify and manage geotechnical hazards, by exploring the following components: Introduction to a questionnaire, which is the main input, and serves as a means for the practitioner to assess the geotechnical engineering activities being conducted on the mine compared to best-practice in the industry. Using a qualitative geotechnical risk matrix to report the status of the primary hazard control classes and the overall geotechnical risk on the mine compared to others in the company. Establishing a reliability index for the geotechnical engineering system (GES) on a mine, which can be used to illustrate how the mine's GES compares to that of a project (ranging from conceptual to feasibility level), design and construction phase, operational phase, and industry best-practice.

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Many publications are available that provide statements of best practice in terms of open pit slope risk management. However, to date none provide a risk model that demonstrates the risk reduction achieved for applying each of the risk management elements. This leaves the slope stability practitioner unable to analytically answer questions such as:  How frequently should slopes be inspected?  How frequently should prisms be read?  Should a radar be acquired? If so, which one?  How many monitoring systems to use? And many more. This paper applies the Venter and Hamman (2018a) temporal safety risk model to an open pit in West Africa. The paper demonstrates the use of the model to a small saprolite open pit and concludes with recommendations for slope instability registers to facilitate future back-analysis in terms of this model.