Tailings Dam
Tailings dams are generally formed by well-engineered containment structures. Unfortunately, failure of these structures and loss of containment are still reported across the world in recent years, releasing both tailings and contaminated water from the storage, resulting in catastrophic environmental, social and economic impacts, or even loss of lives.
Brumadinho tailings dam failure, photo by Ibama from Brasil, CC BY-SA 2.0
Arguably, tailings dams bear a resemblance to water retaining dams. Still, the geotechnical properties of the stored tailings and the non-Newtonian behaviour of the tailings slurries make the failure impact of a tailings dam completely different from water dams. The variability of tailings properties from one mine to the other also makes the failure impact from each tailings dam distinctively different from another.
Jagersfontein tailings pond failure, image by Planet Labs SkySat, used with permission
The importance of Tailings Dam Breach Analysis
The parties involved in the planning, permitting, operating and managing Tailings Storage Facilities (TSFs) include mine owners, design engineers, and regulatory authorities. All parties are highly interested in conducting precise simulations of tailings dam breach scenarios as it allows them to evaluate the severity of the dam failure and the possible impact on downstream areas.
Therefore, predictive modelling and simulation techniques for tailings dam breach analysis (TBDA) have been developed and gradually improved over recent years to facilitate the understanding of the dynamics of the breach flow behaviours.
Animation showing the modelling of TSF failure with downstream flood protection levee (note the first wave of water flood and second wave of tailings flow)
TSF failure impact hazard rating map
A unique approach to comprehensive TDBA
Even before the release of the Global Industry Standard on Tailings Management (GISTM), ATC Williams has always been an industry leader in developing innovative and comprehensive techniques and the most realistic approach for site-specific TDBA. The GISTM has specified that all tailings dam breach analyses need to consider the credible failure modes (regardless of the probability of occurrence) and site-specific parameters and conditions.
TSF failure releasing tailings into the downstream river
Our dedicated TDBA team of highly skilled specialists offers comprehensive TDBA with the following three key advantages:
1. Credible failure modes and scenarios
With our extensive experience in tailings dam design, construction, tailings and water management and facility closure, we understand the ins and outs of a tailings storage facility throughout its lifespan. This capability assists us in the proper assessment of the individual credible failure modes and scenarios.
TSF embankment failure with tailings release
2. Site-specific tailings characteristics
Instead of relying on purely empirical and statistical approaches or published literature data to determine input parameters for dam breach simulation, our team utilise site-specific, in-situ testing data and results from lab testing on representative samples from the site to define the input parameters for dam breach simulation. Information like in-situ tailings density profile, moisture content, strength profile and liquefaction potential all contribute to estimating the post-failure surface and released volume assessment.
Tailings in-situ density profile
Tailings in-situ strength profile
Tailings in-situ strength spatial variations
3. Rheological Properties
It is well-recognised that should the stored tailings in the TSF be identified as liquefiable, the runout of the tailings needs to be modelled as a hyper-concentrated mudflow, which generally behaves as a non-Newtonian fluid (i.e., materials with yield stress and shear rate-dependent viscosity).
At ATC Williams, our Melbourne-based geotechnical and material characterisation laboratory utilises state-of-the-art testing techniques to measure the rheological properties of the tailings samples accurately, even for high solids concentrations which are usually beyond the capacity of routine techniques.
This includes the actual measurement of flow curves (i.e., Shear Stress vs Shear Rate plots) for different solids concentrations and the development of a rheological model (either Bingham Plastic or Herschel-Bulkley models) for the material from the site. The site-specific rheological model parameters are essential inputs to the non-Newtonian tailings flow analysis and tailings runout simulation.
Rheograms
Foreseeing the unforeseen
Comprehensive numerical modelling of the TDBA and flood routing can provide a reference for the designers and dam operators to visualise and assess the potential impact on the downstream area should a dam failure occur. The inundation mapping and failure impact assessment provide direct input toward detailed hazard analysis and consequence category assessment. Furthermore, mitigation strategies, including flood protection levees, diversion channels and Emergency Preparedness and Response Plan (EPRP) can be developed and implemented accordingly.
Tailings dam failure with downstream flood protection levee
Our team is pleased to partner with the client at any stage of the project to assist with the development of a complete understanding of the dam breach failure impact for both water and tailings dams. This approach will lead to establishing a more reliable safety management and emergency response plan.
Please contact the ATC Williams Melbourne Office on 03 8587 0900, Zerui (Thomas) Lu or Dr. Behnam Pirouz to discuss how we can assist you with your project.
Note: all the presented dam break models in this article are non-existent projects and used for demonstration purpose only. Any resemblance to real-life projects is purely coincidental.
