Dam Failure Research Articles

Validation of computational liquefaction for tailings: Tar Island slump

Finite-element analyses using critical state theory proved necessary to understand the development of static liquefaction during three recent large tailing dam failures at Fundao (in Brazil), Cadia (in Australia) and Brumadinho (in Brazil). However, the complexity of these events prevents these analyses being viewed as a complete validation of the methodology. Here the authors evaluate a far simpler case of static liquefaction: the 1974 Tar Island slump (in Canada). This upstream slump involved a rapid drop of 5 m during construction of a 12.5 m high upstream raise over loose tailings. While not a dam stability issue, the event has the attraction for validation of being load-induced, with simple geometry, and with known material properties and in situ state. The computed liquefaction develops from a prior drained condition before propagating rapidly undrained – there are similarities to the video record at Brumadinho (an animation is provided as online supplementary material to illustrate this). A range of scenarios are explored, with the base case of taking reported conditions at face value giving deformations close to those measured. An important aspect was using elastic shear moduli determined by geophysical methods. The analyses were carried out with commercial software (Plaxis) and used critical state theory with largely familiar soil properties measured by standard methods.

Mining Dam Failures in Brazil: Comparing Legal Post-Disaster Decisions.

Mining dam failures have increased worldwide since the 1980s. Two large mining dam failures occurred recently in Mariana and Brumadinho, both in the state of Minas Gerais, Brazil. We hypothesize that there were significant differences in legal post-disaster decisions. The aim of this article is to understand the similarities and differences of post-disaster actions and controversies in Mariana and Brumadinho. We reviewed 686 news reports about court decisions and settlement agreements from the websites of state and federal courts and judicial institutions. After classifying the reports using an adapted protocol from a media health observatory, we conducted a thematic analysis. Our analysis suggests that there were significant differences in legal post-disaster decisions in the cases of Mariana and Brumadinho. In Mariana, there was privatization of post-disaster management, with the creation of the Renova Foundation, a mediated indemnity program, lack of access to information for those affected, and uncertainties in health and resettlement issues. In Brumadinho, there was faster implementation of the recovery and compensation measures, faster recognition of affected parties, and stronger participation of the population since the first hearings. Even though there were particularities in post-disaster management, the ultimate goal of the corporations responsible for the disasters was to protect their profits.

Case History of Risk Evaluation of Earth-Fill Dams Due to Heavy Rain

The present paper describes an assessment method for risks brought on by heavy rain in order to determine the priority of countermeasures for small earth-fill dams. To evaluate the failure risks of an earth-fill dam, defined as the product of failure probability and damage costs, an unsaturated seepage flow analysis is carried out based on the measured rainfall conditions. The damage costs are calculated using the correlation between the results of a flood analysis after breaching and land use and asset data. Subsequently, an evaluation to prioritize the countermeasures is conducted based on the failure risks. The larger of the two comparative failure probabilities—namely, the probability of overflow and the probability of slip failure—will showcase the dominant factor in the failure of small earth-fill dams, and the failure risk evaluation will determine the priority of the countermeasures for repairing and/or reinforcing decrepit earth-fill dams.

Airborne Magnetometry to Identify Metallic Debris to Support Dredging and Search Activities at the Brumadinho Disaster Site – A Case Study

This paper describes the procedures and results of an airborne magnetic survey using Unmanned Aerial Vehicle (UAV) conducted to support Search and Rescue (S&R) teams after the failure of a mining tailing dam at the Corrego do Feijão Mine, in the state of Minas Gerais, Southeast Brazil. The accident claimed 270 lives, practically destroying all the mine’s infrastructure. After the accident, the use of a fast, efficient, and cost-effective method to locate preferential sites for the rescue team to work was critical. Due to the difficulty of direct access to the impacted area, and since most of the affected infrastructure consisted of metallic materials, an airborne magnetometer was the logical choice. First, some performance tests were conducted in order to define the survey configurations, such as flight altitude, transect spacing and anomaly’s detectability threshold. After that, task priorities were set, and the survey area divided in small blocks according to their morphological characteristics using aerial photos of the impacted area. The results showed that the system was able to detect all relevant anomalies. The correlation of the anomalies with aerial photogrammetry helped to discard false anomalies, making the whole operation much more efficient. This increased the effectiveness of the S&R teams as well as the planning of the dredging operations by defining the preferential locations for the interventions.

Application of a critical state model to the Merriespruit tailings dam failure

The use of stress–deformation analyses to evaluate the characteristics of possible static liquefaction events is rapidly becoming the norm for tailings dams exposed to such risk. Ideally, those analyses should be based on constitutive models that incorporate the fundamental mechanics of the problem, are able to perform robustly in commercial numerical platforms and are simple to calibrate. A model that aims to fulfil that specification is proposed. The model is a new implementation of a previously proposed model based on critical state concepts that is able to represent static liquefaction. The model formulation is elaborated to show that all the required inputs can be related to familiar concepts such as the critical state line, the state parameter, the normalised undrained peak strength or the coefficient of earth pressure at rest. The methodology is illustrated by analysing the failure of the Merriespruit tailings dam, which occurred in South Africa in 1994 and was instrumental in the recognition of how widespread liquefaction risk might be in saturated tailings. Numerical analysis of the case showed how a large static liquefaction failure might have been triggered by a relatively small slope erosion caused by overtopping.

Preliminary Risk Assessment of Dam Failure at the Location of the Cukaru Peki Deposit, Bor (Serbia)

Industrial waste landfills, as evidenced by frequent accidents occurring in recent years, are regarded as one of the most hazardous facilities in the world. For the adequate management of a landfill, risk assessments of dam failures should be performed before operations begin. This paper deals with the preliminary risk assessment used for the tailings and pyrite concentrate storage facilities, as well as the drainage waters reservoir, which are currently at the development and construction stage in the Cukaru Peki deposit located in eastern Serbia. The research was conducted to establish the facts and level of risk at an early stage to allow for timely prevention of potential accidents and bring operational practice in line with design requirements. The annual failure probability was estimated using a semi-empirical method, based on the dam stability factor. While, the framework proposed by the New Zealand Society on Large Dams was applied to assess the consequences of potential failures. The risk was assessed as a function of accident probability and the severity of possible consequences, and a 7 × 7 risk matrix was applied for analysis and evaluation. The level of dam failure risk at the location of the Cukaru Peki deposit was preliminarily assessed as moderate and conditionally tolerable, based on a low estimated probability of accident and a significant severity of consequences. Once the operation of these facilities starts risk assessments should be regularly updated, in order to maintain this level, and in accordance with the current situation, the modelling of specific accident scenarios should be included.

An integrated study of the plankton community after four years of Fundão dam disaster

Mining activities can affect the environment either by the tailings releasing or dams failures. The impact of the tailings can last decades and cause chronic effects due to their toxicity. The Fundão dam collapse, a relevant environmental disaster, occurred in November 2015 in Southeastern Brazil. Tailing rich in metals reached the Doce River and arrived in the Atlantic Ocean. Previous studies revealed the acute impact of the tailings in the marine planktonic community near the Doce River mouth. The current study aims to characterize the structure of planktonic assemblages in the impacted area after four years of the disaster. Sampling occurred in November 2018, January, April, and July 2019 at 32 stations located at the marine coastal area near the Doce River mouth. Our study detected high metal concentrations in the surface waters during January 2019, when the lowest diversity and abundance of phytoplankton, lowest zooplankton diversity, and low ichthyoplankton abundance were recorded. The zooplanktonic community was structured by environmental parameters and ichthyoplankton assemblages in November 2018, January and April 2019. Nutrients and metals, mainly iron from the tailing carried by the Doce River waters to the marine environment changed the plankton community, confirming the impact of the Fundão Dam collapse in the coastal area near the Doce River mouth. The phytoplankton community, influenced by the nutrients and to a lesser extent metals concentrations, was not decisive in the zooplankton community structure. The environmental variability was driven by the meteoceanographic conditions and the Doce River flow. There was a high correlation between the zooplanktonic community and ichthyoplanktonic assemblage and the environmental factors and metals. These relations indicate the impact of the tailings from the collapse of the Fundão Dam on these communities, even after four years of the Mariana disaster.

On Dam Failure Induced Seismic Signals Using Laboratory Tests and on Breach Morphology due to Overtopping by Modeling

Dam models were constructed in an indoor flume to test dam breach failure processes to study the seismic signals induced. A simple dam breach model was also proposed to estimate hydrographs for dam breach floods. The test results showed that when the retrogressive erosion due to seepage of the dam continues, it will eventually reach the crest at the upstream side of the dam, and then trigger overtopping and breaching. The seismic signals corresponding to the failure events during retrogressive erosion and overtopping of the dam models were evaluated. Characteristics of the seismic signals were analyzed by Hilbert–Huang transform. Based on the characteristics of the seismic signals, we found four types of mass movement during the retrogressive erosion process, i.e., the single, intermittent, and successive slides and fall. There were precursor seismic signals found caused by cracking immediately before the sliding events of the dam. Furthermore, the dam breach modeling results coincided well with the test results and the field observations. From the test and modeling results, we confirmed that the overtopping discharge and the lateral sliding masses of the dam are also among the important factors influencing the evolution of the breach. In addition, the widening rate of the breach decreases with decreased discharge. The proposed dam breach model can be a useful tool for dam breach warning and hazard reduction.

Improving governance will not be sufficient to avoid dam failures

The last two decades have seen five large tailings dam failures, which developed suddenly and statically with damages of US$ billions and many deaths. These are company-threatening events, far outside societal tolerance, with investors questioning the situation. While media attribute these failures to mining companies, the underlying cause is a failure in engineering education: engineers of record, and their reviewers, lacked an adequate understanding of soil behaviour. The initiative to improve tailings stewardship by the International Council on Mining & Metals, with its focus on process and governance, will not achieve its aims unless this shortfall in understanding of soil behaviour is addressed. Critical state theory quantifies how and why void ratio controls soil behaviour, and was necessary to understand the Fundoa, Cadia and Brumadinho liquefactions (the rapid drained to undrained transition in particular); this critical state framework must become a ‘core competence’ for tailings dam engineers of record. Little additional cost will arise from doing this, with the largest change in practice being adoption of finite-element analysis for stability assessment. The biggest challenge is education, with engineers needing to familiarise themselves with the largely untaught critical state theory (there are public-domain resources for this, as given in the Appendix to this paper).

Process Analysis and Prediction of a Multi-stage Landslide Dam Failure

The studies of mechanism and calculated model of the earth-fill dam and landslide dam have a significant impact on the prediction and risk assessment for dam failure. The present study selected the event of a multi-stage landslide dam failure in southwestern China as a case study. Based on a mathematic model that can consider the failure mechanism, the key parameter can be obtained by back analysis, the twice failure processes can be displayed as well. It indicates that the second landslide dam cannot break under natural conditions, i.e. the landslide dam failure needs manual intervention, which is consistent with the actual situation. Because the landslide would occur again in different cumulated volumes in the future, the dam failure is predicted using the same model. The result illustrates that the maximal flow comes up to 20,000-60,000 m3/s after the dam failure and the failure would occur in a short day. The analysis and prediction provide an improved insight into the landslide dam failure process and risk control.

SIMULATION OF ROCK CRACK AND PERMEABILITY IN DAM FOUNDATION DURING HYDRAULIC FRACTURING

Hydraulic fracturing is one type of thedam internal erosion leading to concentrated leaks and dam failure. During reservoir impounding,cracks in rock or soil can be initiated and expanded by water pressure. The crack expansionincreasesthe permeability of the soil or rock foundations.A numerical model of crack deformationwas established based on the finite elements methodto study crack characteristics due to hydraulic fracturing pressure.The crack of 1 mm wide and 600 mm long is modeled on 1x1 m of rock mass with the overburden pressure and pore pressure in the crack. The permeability of crack rock with orientations was examined using the equivalent permeability based on crack width due to hydraulic fracturing.The results revealed that crack closure variedwith the elastic modulus of the fillerand the orientation along the crack surface. During reservoir impounding, the crack openingswere related to hydraulic pressure and crack orientation. The model of crack opening indicated that the vertical crack orientation was likely to widen more than the horizontal crack orientation,with crack openings in the range0.003-0.37 mm. The range inrock crack permeability with such crack openings was 5x10-6-1.65 m/s thatagreedwell with the range of field permeability based on the Lugeon test of 1.27x10-4 to 4.96x10-3 m/s. Crack openings due to hydraulic fracturing can be used to predict the rock crack permeability within the hydraulic fracturing area in the dam or its foundation.

Numerical simulation of concrete face rockfill dam seepage: case study of Miaojiaba dam, China

Concrete face rockfill dams are widely used in hydropower engineering because of their many advantages. As important structures, if the performance of the concrete face slab and the impervious curtain is weakened, leakages and even serious dam failures can occur. Based on an equivalent quasi-continuum medium model, three-dimensional finite-element numerical simulations of the seepage behaviour of Miaojiaba dam, China, are performed. The seepage field and seepage characteristics, including the phreatic line, maximum hydraulic gradient and seepage discharge, are analysed quantitatively and systematically under various abnormal conditions. The results show that cracks in different areas of the face slab and different degrees of degradation in the impervious curtain influence the seepage field in different ways, with cracks in the lower face slab being the most serious. Ensuring that the face slab and impervious curtain are working as intended is very important for the integrity of the dam. Therefore, the design and construction quality of impervious structures should be strictly controlled. Under abnormal conditions, seepage control should be realised to ensure the safety and stability of concrete face rockfill dams.

A comprehensive evaluation of the consequences of dam failure using improved matter element analysis

A comprehensive evaluation of the consequences of dam failure using improved matter element analysis

Integrated Water-Power System Resilience Analysis in a Southeastern Idaho Irrigation District: Minidoka Case Study

This study investigates the joint water–power system resilience of an irrigation district in southeastern Idaho. Irrigation districts face difficulties in the delivery of water to farmers under drought conditions, during equipment failures, or unplanned infrastructure disruptions. The resilience of interconnected water and power systems can be better analyzed and understood through an integrated approach, using a model that connects the dependencies between the two halves of the system. Using a multi-agent system model capturing both water and power system components, as well as their linkages, we capture the interdependencies of these systems and highlight opportunities for improvement when faced with disruptions. Through simulation scenarios, we examine the system resilience using system performance, quantified as the percentage of met demand of the power and water system, when subjected to drought water year, an unforeseen water demand increase, power outage and dam failure. Scenario results indicate that the effects of low flow years are mostly felt in the power system; unexpected increases in water demand marginally impact irrigation system performance; dams and pumps present vulnerabilities of the system, causing substantial unmet demand during disruptions. Noting the interdependencies between the water–power system halves while leveraging an integrated simulation allows for an insightful analysis of the system impacts during disruptions.

Post-peak behavior of concrete dams based on nonlinear finite element analyses

Dam failures are catastrophic events and in order to improve safety, engineers must have good tools for analysis and an understanding of the failure process. Since there are few cases of real failures in concrete dams, which can work as validation, physical model tests are a good way of improving numerical models and the understanding of the failure process. In this article, a physical model test of the buttress from a concrete Ambursen type dam is used as a benchmark for calibrating a FE-model. The dam failure is thereafter simulated using the concept of safety commonly used in the design codes. The advantages and drawbacks of performing load- and displacement-controlled simulations are compared. A new method for performing displacement-controlled simulations, using nonlinear springs to introduce the hydrostatic pressure and ice load is thereafter suggested and tested. The proposed method gives results which corresponds to the classical methods of analysis but has some advantages. Primarily, the new method is stable and does not suffer from convergence issues as was the case with the other methods. It is also simple to introduce in most commercial software compared to classical displacement-controlled simulations.

Instrumented flume tests on the failure and fluidization of tailings dams induced by rainfall infiltration

Although numerous studies focus on the mechanical behaviour and instability of tailings dam materials, a framework that adequately describes all the processes involved in their failure and fluidization is still needed. Therefore, we used a series of instrumented flume tests, with pore pressure transducers, micro-seismic accelerometers, internal displacement transducers and laser scanning, to investigate the mechanisms of tailings-dam failure and fluidization. The artificial rainfall induced water infiltration was adopted to induce the failure. The test results showed that continuous rainfall expanded macro-voids and led to particle rearrangement and local collapse, producing a gradual buildup of pore pressure. Furthermore, the increasing porosity enhanced seepage forces and thus reduced the shear strength of the tailing's materials so that the dam models were close to liquefaction. However, a dam model with a higher hydraulic conductivity would not be totally damaged, even if failure and fluidization occurred. The amount of antecedent rainfall likely significantly contributed to dam failure because it raised the moisture content of the tailing's materials, which promoted internal erosion; thus, the rainfall might have been sufficient to generate local fluidization. Rainfall decreased the peak pore pressures required to initiate failure and shortened the time to failure but hardly influenced the fluidization movement distance.

Do metals differentiate zooplankton communities in shallow and deep lakes affected by mining tailings? The case of the Fundão dam failure (Brazil)

The effects of exposure to mining tailings on water quality and biota of tropical lacustrine ecosystems remain poorly understood. We tested the hypothesis that after mining tailing spills, shallow lakes should retain higher metal concentrations in comparison with deep lakes, which might contribute to differentiating species sorting and community structure of zooplankton in both ecosystems. Surveys were performed in 6 Brazilian lakes affected by the Fundão dam failure from October 2018 to September 2019. The shallow lakes showed higher values of turbidity (19.4 ± 12.9 NTU), conductivity (846.5 ± 1727.1 μS.cm-1), total organic carbon (11.6 ± 4.6 mg.L-1), total nitrogen (2688.7 ± 2215.6 μg.L-1), iron (2507.5 ± 726.9 μg.L-1), aluminum (419.9 ± 166.5 μg.L-1) and manganese (150.8 ± 146.2 μg.L-1) and lower zooplankton richness (9.2 ± 3.2) compared to the deep lakes (13.4 ± 3.0), which showed higher cyanobacteria density (84.7 103 ± 69.3 103 cel.mL-1). We recorded negative relationships between zooplankton richness and turbidity, conductivity, iron, zinc and vanadium, indicating that as well as morphometric characteristics of lakes (area and depth) have an important role in zooplankton richness, the coupling between metals and limnological variables represent decisive environmental filters for species sorting of zooplankton. The variation-partitioning analysis showed that limnological variables and metals explained zooplankton composition, highlighting that metals play major influence on zooplankton composition. We suggest that the shallowness of the lakes should had promoted often resuspension of mining tailings that caused increases in metal concentrations in water column. The results indicate that the shallow lakes presented higher vulnerability to mining tailings exposure than the deep lakes, which may have substantially contributed for differentiating zooplankton communities in both ecosystems. This study reveals the need for considering shallow lakes as priority target for conservation among freshwater ecosystems affected by mining tailings.

Experimental study on discharge impact characteristics induced by piping failure of tailings dam

Experimental study on discharge impact characteristics induced by piping failure of tailings dam

Interpretasi Instrumentasi Piezometer Dalam Rangka Pemantauan Keamanan Bendungan Kedung Ombo

The embankment dam is the most widely built dam in the world, especially in Indonesia. However, embankment dams are also prone to collapse. Dam failures due to the piping process through the dam body account for 30.5% of the total dam collapses worldwide. Therefore, it is necessary to periodically monitor and evaluate the condition of pore water pressure and seepage in a dam which is usually carried out using installed instrumentation. Very little has been done on instrumentation interpretation of earthfill dams in Indonesia, which is a very worrying condition. It is possible that old or even new dams have shown behavior that leads to a decrease in safety. This condition can be monitored by instrumentation in the dam if interpreted properly. Kedung Ombo Dam as an old embankment dam but has a fairly complete instrumentation can be evaluated for safety related to pore water pressure and phreatic line (seepage line). Pore water pressure evaluation is carried out by collecting piezometer readings and reservoir water level fluctuations over a period of several years. The results of the research on the interpretation of piezometer readings indicate that the overall safety of the Kedung Ombo dam is still good in terms of pore water pressure conditions. However, there are some anomalous conditions that should be investigated further

The formation and geometry characteristics of boulder bars due to outburst floods triggered by overtopped landslide dam failure

Abstract. Boulder bars are a common form of riverbed morphology that could be affected by landslide dams. However, few studies have focused on the formation and geometry characteristics of boulder bars due to outburst floods triggered by landslide dam failure. In such a way, eight group landslide dam failure experiments with a movable bed length of 4 to 7 times the dam length with 25 boulder bars were carried out. In addition, 38 boulder bars formed in the field triggered by four landslide dam failures were investigated. The aim of this paper is to study the formation and geometry characteristics of boulder bars along the riverbeds. The results show that boulder bars are formed after peak discharge of outburst flow. The number of boulder bars is 0.4 to 1.0 times the ratio of riverbed length to dam bottom length. Besides, boulder bars have the characteristic of lengthening upstream during the failure process. A boulder bar's upstream edge has a more extensive development than a boulder bar's downstream edge. The length of a boulder bar along the channel changes faster than the boulder bar's width and height. After the dam failure, the boulder bar's length is about 8 to 14 times its width. The relationship between the ratio of boulder bar length to width and the boulder bar's dimensionless length could be described with a hyperbolic equation. The dimensionless area of the boulder bar increases linearly with the dimensionless area of the river section, and the linear ratio is about 0.5. With the field data, this demonstrates that the formation and geometry characteristics of boulder bars in tests are consistent with the field boulder bars. Therefore, the results in this paper are credible and can be applied to the riverbed's geomorphological characteristics analysis triggered by overtopped landslide dam failure. The plentiful experimental and field data could contribute to the community boulder bar research.