Tailings storage facility (TSF) design has long been based on deterministic limits. By extension, the TSF owner accepts a Probability of Failure (PF) associated with these deterministic limits which are assessed against industry norms with respect to investigation/analysis and design assumptions related to the operation of the facility. If the Probability of Failure of a design that is derived in this way is taken as the likelihood related to the tolerable risk limit, it follows that the same, or a lower PF, should be maintained during operations. Examples of operational controls include pond management and inspections/monitoring. Upset conditions arise when operational controls are not being implemented. Therefore, by comparing the calculated PF of the TSF complying with the design assumptions and the PF for the same TSF in an upset condition, the required PF of operational controls can be estimated. This concept assists the TSF owner in determining what is required to safely operate the facility and communicate the geotechnical risk to all stakeholders. By extension, scenarios where a TSF owner cannot achieve the required PF of operational controls can be addressed with: 1. Greater rigor applied to operational controls. 2. Addition of more operational controls. 3. A change to the design assumptions, where the timing of the project allows. This method provides a measured approach to risk management in the design and operational phases, without a TSF owner having to quantify an acceptable risk tolerance. Instead, the design is based upon widely accepted practice and industry/business accepted safety, economic and environmental risk levels. Subsequently, the design PF can be calculated and then applied as a benchmark for operations. This approach serves to reduce uncertainty through alignment of the design and operation phases. The concept is explored for three different tailings storage methods: upstream raised TSF, downstream raised TSF, and impoundment by mine waste dumps, to estimate how sensitive each storage method is to the type and effectiveness of operational controls implemented by the dam owner.
Inherent uncertainty associated with the selection of input parameters to various geotechnical analyses often results in the likelihood of failure being a dominant topic in the discussion of risk associated with geotechnical assets. As a result, embankment failure is the default risk scenario driving ongoing management of tailings storage facilities (TSFs). This commonly applied approach is inefficient as it drives resource intensive TSF management and limits scope for a risk-based approach. However, many TSFs operate with several layers of controls in place. Therefore, assessment of risk with consideration of these controls would promote greater efficiency in TSF management. A fit for purpose approach will be discussed that demonstrates how risk can be utilised as the foundation for the development of a management framework for a single or portfolio of TSFs. This approach focuses on the identification and monitoring of controls, based on the understanding that hazards impact when the controls put in place to manage them fail. It is necessary to build such an approach with the full application of risk principles, which will be introduced by a specialist in corporate risk. Topics covered include a brief history of risk, importance of control effectiveness in scenario selection and risk evaluation and communicating value at risk to drive resource allocation. It is hoped that this discussion and presentation of simple examples allows risk concepts to be better applied to the design and management of geotechnical structures.
Thin spray-on liners (TSLs) provide areal support to rock excavation surfaces, and have been implemented in the mining sector for over 20 years. However, scepticism over their usage still prevails, despite the results of laboratory research that has been carried out indicating their effectiveness for use in mines. The study described in this paper aims to highlight TSL performance as viewed by the mining industry. Some underground cases of practical performance have been singled out and compared with the expected performance based on information from suppliers and from laboratory testing perspectives, and the causes of the resulting quality of performances were categorised. Among the causes of the discrepancies between expectations and observations is the lack of inclusion of parameters such as temperature and humidity in the laboratory tests, which could have significant effects on the liner performance since, based on results from Brazilian indirect tensile tests on coated samples, their inclusion doubles the probability of failure and therefore, increases the predicted geotechnical risk of failure. Consequently, to take into account potential performance discrepancies, some existing recommendations and further potential recommendations are suggested in the paper. If later validated, these suggestions could be included in a good practice guideline for TSL application in underground mines.