Gideon Steyl, Ralph Holding, Lis Boczek
A Monte Carlo method for assessing liner systems is applied with outcomes demonstrating the range of discharge that could occur over the liner interface. The Monte Carlo approach allows for variation of fill material over the liner system and includes the assessment of a second compacted zone either above or below the liner zone. In this paper clay liners were evaluated due to regulatory guidelines and it could be demonstrated that similar performance to a 1 m clay liner could be attained using compacted material to reduce discharge over the liner interface. The approach applied in this paper allows for at least a worst-case quantification of seepage risk which could be included in liner selection criteria or presenting liner options to regulators.
Hench Wang, Peter Hill, Sam Banzi, Muhammad Hameed
Dam owners can often struggle to demonstrate the dam safety risk benefits that can be achieved through non-structural risk reduction measures, such as adoption of smart technological solutions that improve the timeliness and quality of decision making. WaterNSW collaborated with HARC to develop a novel way of demonstrating benefits from improved data management. This paper discusses the use of HEC-LifeSim to demonstrate the reduction in life safety risk from improved monitoring through DamGuard for a case study dam in Sydney. DamGuard is a real-time dam safety monitoring system implemented by WaterNSW. This case study was the first time in Australia where a simulation model such as HEC-LifeSim was applied to quantify the life safety risk benefits pre and post the implementation of DamGuard. The implementation of DamGuard to the sample dam was estimated to reduce the life safety risk by 15%.
Ryan Singh, Jiri Herza, James Thorp
Recent and continual failures of tailings storage facilities (TSFs), often resulting in catastrophic consequences, has led to calls for action from the industry, stakeholders and the public at large. Several standards and guidelines are being prepared at the time of writing, most notably a Global Industry Standard on Tailings Management (GISTM), with the overall objective to reduce the rate of TSF failures globally. While better guidelines are certainly necessary, there are requirements that must be carefully followed in developing a document that has the ambition to become a standard. If such requirements are not fulfilled, the document can become ineffective or potentially have the opposite result to that which was intended. This paper discusses whether or not the GISTM meets the requirements of the standards and analyses the potentially negative impacts of its implementation on the industry and wider society. Based on this analysis, this paper provides several recommendations for improvements that should be considered by the GISTM panel and other working groups preparing standards and guidelines.
Qian Gu, Joshua Chan
Tailings Storage Facilities (TSF) constructed using upstream methods may have static liquefaction risks due to the strain softening behaviour of contractive tailings. Conventional Limit Equilibrium Analyses (LEA) using either peak strength or residual strength fail to address the stress-strain compatibilities between materials at different stages of softening or hardening, resulting in over or underestimating embankment stabilities. Static numerical analyses (Finite Element or Difference) are unable to identify the threshold stability due to their inability to converge close to or beyond equilibrium conditions.
In this study the failure triggering process is modelled with dynamic Finite Element Analyses (FEA) with the stress-softening behaviour of contractive tailings simulated by Norsand Model. The embankment failures are identified by either non-zero residual velocities along downstream face, or a drop in average shear stress along potential failure surfaces under increasing disturbing surface pressure. Threshold disturbing surface pressure estimated using these two methods are in close agreements. Factor of Safety (FoS) values estimated from peak mobilised shear strength are found to be between those estimated using the peak and residual shear strength in LEA. q-p’ stress paths in tailings clearly show the stress ratio increasing towards and beyond instability ratio during undrained triggering process. The developments of zones of shear softening and p’ reduction with increasing undrained disturbances help visualise the failure triggering process.
Michael Ashley, John Phillips
New guidance and publications relating to tailings dams have been released recently by many jurisdictions across the world as an initial response to recent, well-documented, catastrophic tailings dam failures. The application of new guidelines retrospectively to existing tailings projects can introduce complex challenges, especially for sites with a long and often not well documented history. Challenges can be difficult to overcome while balancing time, cost and risk objectives.
This paper explores the impacts of changes between the 2012 and 2019 revisions of the ANCOLD Guidelines on Tailings Dams and potential implications for existing facilities.
The most significant update between the 2012 and 2019 revisions of the guidelines relating to design practices is the additional detail and guidance on seismic stability analyses and static liquefaction. Guidance on the application of new guidelines for tailings dam designers, owners and regulators is required to provide a consistent approach to manage the risk.
James Thorp, Ryan Singh, Jiri Herza
Responsible management and operation of tailings and water storage facilities comprises a series of activities and projects that must be delivered within the commercial realities of the organisation and operation context of the facility owner. All projects are constrained by several variables, which are commonly represented by the Project Management Triangle of Scope, Time, and Cost. These variables are often finite and mutually exclusive, and delivery of the required outcome is accomplished by successfully managing each variable. The activities (variables) associated with the long-term dam safety are sometimes omitted to meet the immediate project requirements. In addition, the commercial realities, such as a selected project delivery model, can have a significant impact on dam safety risks through the allocation of risk, ability of the key decision makers, and the undue commercial pressures applied by each project delivery model. This paper presents several case studies where the project and commercial realities have led to decision making that impacted dam safety and increased the risk presented by the storage facility. While the immediate impact of these decisions may appear to be minimal, all stages of a tailings or water storage facility’s life span are impacted. This paper presents learnt lessons with the aim to prompt both owners and consultants to reconsider their commercial processes and project delivery strategies and limit unforeseen risks to the safety of tailings or water dams.