Tailings Dams — Some Aspects of Their Design and Construction

Tailings material from the existing Sishen plant is currently being deposited on four individual tailings dams. The solids concentration of the tailings can not be increased by means of thickening as the current process can not deal with flocculant. Decant water from each tailings dam is transferred into two seepage sumps via gravity penstock decant systems from where the water is returned back to the Sishen plant. The water balance and water recovery for the current Sishen tailings disposal system is not optimised and the dams are used on a random basis for the storage of storm rainfall and excess process water. The deposition cycle on the dams in terms of layer thicknesses and cycle times was not optimised. Significant evaporational losses therefore occur which is not ideal for an operation in such an arid climate. The Sishen Expansion Project (SEP) involves the establishment of a separate process plant. Tailings material from the SEP plant will be disposed off in the cross area in between the current four individual tailings dams. One leg of the cross area will be closed off at a time and filled with SEP tailings materials. It is planned to fill the four legs of the cross area over a period of approximately 10 to 12 years. The SEP will increase the current water consumption and has prompted the optimisation of the tailings dam complex water balance. Once the cross area is filled up to the same level of the four individual tailings dams, the four dams and the filled cross area will be consolidated into one single dam with four operating paddocks. The principle of operating four paddocks with optimised deposition strategies and small pool areas contributes towards improved water recoveries. The method of tailings disposal and dam operation also remains the same as per the current operations. A return water dam (RWD) will be constructed as part of the SEP. The RWD will consist of an operating compartment capable of containing five days operational storage. Any run-off water from a 1:50 year 24 hour rainfall event on top of the tailings dams will be contained on top of the tailings dams and decanted in the shortest period of time possible. This paper will discuss how the water consumption of the Sishen tailings dam complex was improved by conventional means other than thickened tailings. The improved water consumption over the life of mine will also be discussed.

Tailings dam is an important control project of mine safety, once the instability, the greater harm.Tailings dam seepage damage is the main reason about tailings dam safety accident and tailings dam seepage problem belongs to the muddy water seepage.By considering the main hydraulic factors of the seepage problem, use finite element software to analyze its seepage stability.Test the safety of dam running state and get the influence law of permeability coefficient and aquitard on dam safety.

Study on the Risk Assessment of the Tailings Dam Break

Gold and uranium tailings (‘slimes’) dams and the adjacent polluted soils in the deep-level mining regions of South Africa (Carletonville, Klerksdorp and Welkom) were surveyed for the frequency of occurrence of naturally colonizing, actively introduced and persisting plant species. Fifty-six tailings dams with a combined area of 5864 ha. and a similar area o f tail- ings-polluted soils, were surveyed between July 1996 and March 1997. During the survey, 376 plant species and subspecies were recorded from the dams and adjacent polluted soils, with an additional 8 6 records obtained between 1998 and 2003 (i.e. a total of 462 taxa: species and infraspecific species). Overall, the most commonly represented families were the Poaceae (107 species and subspecies), Asteraceae (81). Fabaceae (55) and Anacardiaceae (16). with other families represented by just one to 14 species. Only 60 species were common to all three regions, and of these 24 had been introduced during rehabilitation attempts. Most of the species found on tailings were persisters or natural colonizers (53-88%, depending on substrate), with the vast majority being indigenous and perennial taxa (76% and 85% respectively), with semi-woody to woody growth forms (6 6% being resprouters, forbs, shrubs and trees). Less than 4% of the naturally-colonizing taxa found during the survey had also been introduced by vegetation practitioners. The majority of introduced plants were alien herbaceous taxa. The number and frequency of annuals was only high on recently vegetated sites, whereas annuals were rarely present on old-vegetated and never-vegetated dams. This list includes a wide range of indigenous plant species that may be suitable for phytoremediation of tailings dams and polluted soils due to their apparent tolerance of acid mine drainage and salinity.

In February 2007, a tailings dam used as sedimentation pond of lime particles failed. As a result, an estimated volume of 150,000m3of tailings flowed from the breach in the dam slope. Forensic investigations were carried out to determine the causes of failure, so that suitable changes could be made for the future safe operation of the tailings disposal facility. The investigation identified several features of the tailings material and dam behaviour that it is considered contributed significantly to the slope failure. Among them, a marked anisotropy in the effective shearing resistance of the tailings material and the water accumulation in the tailings were identified as important factors in the failure. The origin of the anisotropy is the method of tailings deposition per layer, and results in a much lower shearing resistance on horizontal planes. The water accumulation was the consequence of a permeability of the tailings being higher than expected due to shrinkage fissures and a significant reduction in drainage efficiency from below the tailings. This loss of drainage was due to precipitation of calcite that lowered dramatically the permeability of the granular soils. The objective of the paper is to illustrate through back-analysis of the tailing dam failure how the shear resistance anisotropy and the efficiency of the drainage system influences the safety factor of the tailings dam.

The demand for tailings storage, and in turn the associated risk, is increasing exponentially with time. It has been estimated that the potential risk posed by tailings dams increases by 20-fold approximately every 30 years, as tailings storages become larger, are built faster and must remain stable for longer. The social, environmental, and economic consequences of tailings dam failures are globally significant, and more readily scrutinised and observed by the general public than ever. As a persistent liability, how does the tailings dam avoid being dismissed as an expenditure until such time as a serious deterioration or failure occurs?In hindsight, there have been no tailings dam failures that are unexplainable. Through the appropriate investigation into their root causes, each and every failure has been able to have its mechanism described using the data available. Switching this to a proactive perspective, it is suggested that through access to and the use of the appropriate design and construction, and operational and monitoring approaches, tailings dam practitioners can be more readily equipped to understand and foresee the deterioration of their unique tailings dam structure. In turn, this allows for a safer, collaborative approach between the different stakeholders and provides a vessel for healthy and informed discussion and decision-making. Today, challenges arise in identifying and utilising monitoring systems to understand the complex performance and rapid behaviours of these dams, in turn reflecting on the system’s ability to be able to predict deterioration before failure occurs.This thesis developed a comprehensive monitoring strategy for tailings dams. Focusing predominantly on onsite monitoring techniques, the research explored the role that appropriate monitoring can play in understanding and assessing the performance of the dam against its expected behaviour. The research explored the state of practice for monitoring techniques, developed catalogues of instrumentation types and the systems that these integrate with in practice, described analysis techniques in relation to risk management processes in combination with the observational approach and numerical model calibrations, and demonstrated the effectiveness of these techniques through a number of case studies.The research found that by appropriately acknowledging the advantages and limitations of different monitoring methods, tailings dam practitioners have the opportunity to foresee certain types of failure ahead of time and implement appropriate responses prior to a catastrophic consequence. Monitoring strategies and technologies need to be simple and user-friendly enough to accommodate the cost-effective collection of information, which introduces a shared responsibility between operators, suppliers, and designers. The data collected from different instrumentation should fundamentally link to potential failure modes and should be used to iteratively update original design assumptions and the design intent of a safe, stable and non-polluting tailings dam. The research acknowledged the variability of tailings dam environments, while reiterating a focus on core mechanisms and the understanding gained from geotechnical theory, lessons learned from previous failures, and a structured baseline approach allows tailings dam practitioners to spend more of their time focused on the unique challenges onsite. Collaboration between the global community of tailings dam practitioners is needed, whereby data are proven to enable greater understanding through real demonstration of the trends, patterns, and data behaviour.

Tailings dams: Assessing the long-term erosional stability of valley fill designs

Geomorphologic risk zoning to anticipate tailings dams' hazards: A study in the Brumadinho's mining area, Minas Gerais, Brazil

The upstream valley-type tailings dam exhibits a longitudinal profile that resembles an inverted triangle or a shape approximating an inverted triangle. This unique dam structure and its mechanical characteristics mean that the influence of longitudinal stress on the stability of the dam cannot be overlooked. However, the two-dimensional Swedish slip circle method calculation model does not take into account longitudinal stress, necessitating the development of a three-dimensional model specifically for the stability analysis of upstream valley-type tailings dams. Utilizing the Beijing Lizheng Geotechnical Calculation Software 5.3 standalone version, a three-dimensional calculation model was constructed based on the Swedish slip circle method. Taking the Cangyuan Jinla Lead-Zinc Mine tailings dam as an engineering example, this model was used to calculate five cross-sections, including 1–1′, of the dam. The results were then compared and analyzed with those obtained from the Swedish slip circle method, the simplified Bishop method, and the Janbu method. Using this three-dimensional model, the safety factors for cross-sections 1–1′, 2–2′, 3–3′, 4–4′, and 5–5′ of the tailings dam were calculated to be 2.798, 1.348, 1.332, 1.466, and 2.134, respectively. Analysis concluded that the most dangerous sliding surface of the tailings dam is located at the 3–3′ cross-section, with an overall dam safety factor of 1.332, indicating that the tailings dam is in a relatively stable condition. The safety factor of the tailings dam calculated using the finite element software MIDAS is 1.3531, verifying the accuracy of this three-dimensional model. For upstream valley-type tailings dams, the results from ordinary two-dimensional models tend to be on the dangerous side and thus should be corrected using this three-dimensional model to obtain more accurate and conforming safety factors.

A method for assessing the long-term integrity of tailings dams

The mining is an activity of importance to the world economy moving billions of dollars/years and employing a network of people. After the tragedies observed in Brazil over mining dams, reflections have been raised about the safety of these environments and their impacts on the environment. This paper focused on compliance weakness on tailing dams' regulations in Brazil and the impacts of environmental accidents in Canada. Besides that, it did a bibliometric analysis with tailing dams’ strings/terms relationed and a comparative Brazil-Canada, a developed country where a similar accident with a tailing dam happened. It discussed the following topics: Salient keywords and Emerging themes, temporal and geographical distribution of publications; growth publication; word cloud, the federal legislation, and instruments for safety of dams, regulations, and the role of inspections agencies, tailing dam accidents and the Canadian scenario of mining regulations and make a comparison between these two countries.

Rehabilitation of a tailing dam at Shimen County, Hunan Province: Effectiveness assessment

Tailings dams are structures that store both tailings and water, so almost all tailings dam accidents are water related. This paper investigates a tailings dam’s failure pattern and damage development under flood conditions by conducting a 1:100 large-scale tailings dam failure model test. It also simulates the tailings dam breach discharge process based on the breach mode using FLOW-3D software, and the extent of the impact of the dam failure debris flow downstream was derived. Dam failure tests show that the form of dam failure under flood conditions is seepage failure. The damage manifests itself in the form of flowing soil, which is broadly divided into two processes: the seepage stabilization phase and the flowing soil development damage phase. The dam failure test shows that the rate of rise in the height of the dam saturation line is faster and then slower. The order of the saturation line at the dam face is second-level sub-dam, third-level sub-dam, first-level sub-dam, and fourth-level sub-dam. The final failure of the tailings dam is the production of a breach at the top of the dam due to the development of the dam’s fluid damage zone to the dam top. The simulated dam breach release results show that by the time the dam breach fluid is released at 300 s, the area of over mud has reached 95,250 square meters. Local farmland and roads were submerged, and other facilities and buildings would be damaged to varying degrees. Based on the data from these studies, targeted measures for rectifying hidden dangers and preventing dam breaks from both technical and management aspects can be proposed for tailings dams.

Soil and vegetation development along a 10-year restoration chronosequence in tailing dams in the Xiaoqinling gold region of Central China

Based on the engineering geological, hydrogeological conditions and survey results of Zhelamuqing tailings dam, two types seepage problems in the tailings dam which are saturated seepage and saturated - unsaturated seepage were described and solved by Darcy law and Richards Equation respectively. Then the three-dimensional seepage field of tailings dam under steady saturated state was simulated by finite element method (FEM). And the seepage line of saturated - unsaturated seepage field in the tailings dam was simulated and predicted by numerical analysis method when the embankment is enduring the flood. Subsequently, the simulated seepage line of saturated - unsaturated seepage field in the tailings dam was verified by the survey result. Results show that it is feasible to describe the saturated seepage and saturated - unsaturated seepage by means of Darcy law and Richards Equation respectively and it is effective to simulate the three-dimensional seepage field of tailings dam under steady saturated state by using the finite element software Midas GTS. Results also show that the simulated seepage line of saturated - unsaturated seepage field in the tailings dam agree with the survey result.