A detailed search and re-evaluation of the known historical cases of tailings dam failure was carried out. A corpus of 147 cases of worldwide tailings dam disasters, from which 26 located in Europe, ...was compiled in a database. This contains six sections, including dam location, its physical and constructive characteristics, actual and putative failure cause, sludge hydrodynamics, socio-economical consequences and environmental impacts. Europe ranks in second place in reported accidents (18%), more than one third of them in dams 10-20m high. In Europe, the most common cause of failure is related to unusual rain, whereas there is a lack of occurrences associated with seismic liquefaction, which is the second cause of tailings dam breakage elsewhere in the world. Moreover, over 90% of incidents occurred in active mines, and only 10% refer to abandoned ponds. The results reached by this preliminary analysis show an urgent need for EU regulations regarding technical standards of tailings disposal.
One of the leading causes of dam failure is internal erosion. The impact of erosion of non-plastic fine particles, known as suffusion, on the soil structure and strength has been studied ...experimentally. However, influences including sample size have not been thoroughly investigated. Internally unstable gap-graded cohesionless soil samples with various sizes were investigated using an erosion-triaxial apparatus. Samples were subjected to downward inflows of different seepage velocities. The results indicated that the potential for clogging increased with an increase in specimen length, leading to less fine particle erosion. Internal erosion changed the mechanical soil behaviour even after the loss of fines equal to 5% of the overall sample volume. Eroded specimens with similar intergranular void ratios showed similar undrained post-erosion behaviour. However, the magnitude of the post-erosion initial undrained peak shear strength is a function of coarse particle interlocking, residual fine content, and equivalent intergranular contact index. It was also found that the steady state line remained unchanged after erosion of fine particles and the mobilized friction angle at the steady state line is independent of the residual fine content.
In November 2015, a large mine-tailing dam owned by Samarco Corporation collapsed in Brazil, generating a massive wave of toxic mud that spread down the Doce River, killing 20 people and affecting ...biodiversity across hundreds of kilometers of river, riparian lands, and Atlantic coast. Besides the disaster's serious human and socioeconomic tolls, we estimate the regional loss of environmental services to be ~USS521 million per year. Although our estimate is conservative, it is still six times higher than the fine imposed on Samarco by Brazilian environmental authorities. To reduce such disparities between estimated damages and levied fines, we advocate for an environmental bond policy that considers potential risks and environmental services that could possibly be impacted by irresponsible mining activity. Environmental bonds and insurance are commonly used policy instruments in many countries, but there are no clear environmental bond policies in Brazil. Environmental bonds are likely to be more effective at securing environmental restitution than post-disaster fines, which generally are inadequate and often unpaid. We estimate that at least 126 mining dams in Brazil are vulnerable to failure in the forthcoming years. Any such event could have severe socialenvironmental consequences, underscoring the need for effective disaster-management strategies for large-scale mining operations.
AbstractInternal erosion involves selective loss of fine particles within the matrix of coarse soil particles under seepage flow, which affects the hydraulic and mechanical behavior of the soil. In ...this research, extensive laboratory internal erosion tests were conducted under complex stress states following three stress paths: isotropic, drained triaxial compression, and triaxial extension stress paths. These tests were designed to investigate the initiation and development of internal erosion and the effect of stress state on critical hydraulic gradients. The entire erosion process can be divided into four phases: stable, initiation, development, and failure. Accordingly, three critical gradients termed as initiation, skeleton-deformation, and failure hydraulic gradients, can be defined. These critical gradients correspond to the onset of erosion of the fine particles filling the large pores of the skeleton, the buckling of the strong force chains formed by the coarse particles, and the soil failure, respectively. The initiation gradient under compression stress conditions generally increases with the shear stress ratio first and then decreases when the stress conditions approach failure. The tests under isotropic stress conditions show the largest initiation and skeleton-deformation gradients at the same porosity.
Simulation of dam breach scenarios can help in the preparation of emergency action plans for real dam breaks or flash flooding events. The purpose of this study was to identify flood-prone areas in ...the Al Wala Valley in the governorate of Madaba in Jordan through analysis of the Al Wala Dam. Modelling of dam breaches was conducted under two scenarios: a Clear Day scenario and a Probable Maximum Flood (PMF) scenario. The former scenario does not address the various dam failure modes; rather, it addresses the formation and development of a breach as a result of structural failures like the sliding of dam blocks in the case of a concrete dam or piping failures in the case of embankment dams. The PMF scenarios, however, simulate unsteady flow in pipes and overtopping failure via consideration of runoff hydrography. In the PMF scenario, flood-prone areas can be identified by in-depth analysis of data from previous extreme rainfall events. The related hydrologic and hydraulic data can then be modelled using intensity-duration-frequency curves applied to an hour-by-hour simulation to discover the areas most at risk of flooding in the future. In the present study, data were collected from inlet of flow to Al Wala Valley on 10 January 2013. The collected data, which included rainfall and discharge data, were fed to the HEC-HMS software in order to calibrate the hydrological parameters of the watershed of the Al Wala Dam. Additionally, the HEC-RAS tool was employed to determine the breach outflow hydrography and hydraulic conditions across various critical downstream locations, which were determined by use of dynamic flood wave-routing models. The simulations revealed that, in the case of the Clear Day scenario, downstream inundation would cover an area of 5.262 km2 in the event of a pipe failure. However, in the event of a six-hour storm, a twelve-hour storm, and a twenty-four-hour storm, the flooded area would rise to 6.837 km2, 8.518 km2, and 9.390 km2, respectively. In the event of an overtopping failure, 13.171 km2 would be inundated, according to the Clear Day scenario. On the other hand, in the event of a six-hour storm, a twelve-hour storm, and a twenty four-hour storm, the flooded area would rise to 13.302 km2, 14.249 km2, and 14.594 km2, respectively.
AbstractDike risk management requires breaching parameters that can be estimated rapidly to support the prediction of inundation zones and decision making. The objectives of this paper are to compile ...a database of dike breaching cases, study common dike failure mechanisms, and develop a set of empirical equations for estimating breaching length, depth, and peak discharge. A database of over 1,000 dike failure cases was collected, with information on pre-breach dike geometry, materials, type of dike, failure mechanisms, breaching length, depth, and peak discharge. A set of regression models are formulated using five control variables: dike height, width, material, type of dike, and failure mechanism. The standard error is set as a selection criterion and the Akaike information criterion is used to optimize the proposed empirical models. The new models are validated using independent cases and compared with available empirical equations for dikes and man-made dams.
AbstractInternal erosion is a major cause of dam or dike failures and incidents. In this study, laboratory tests were conducted to investigate the deformation of two gap-graded soils during internal ...erosion and the stress-strain behavior of the soils that experienced loss of fine particles due to internal erosion. An erosion-controlled experimental method was adopted to achieve a designated loss of fine particles during internal erosion by adding a predefined amount of salt into the soil sample during sample preparation and dissolving the salt in water under a controlled stress condition. Both the radial and axial deformations during erosion were measured using a photographic method. Subsequently, drained triaxial compression tests were performed to study the stress-strain behavior of the soils that had lost different amounts of fine particles. The peak friction angle and critical friction angle of the soil decreased with the loss of fine particles. After a significant loss of fine particles, the stress-strain behavior changed from the initially dilative behavior to a more contractive behavior.
A hybrid model integrating chaos theory, support vector machine (SVM) and the difference evolution grey wolf optimization (DEGWO) algorithm is developed to analyze and predict dam deformation. ...Firstly, the chaotic characteristics of the dam deformation time series will be identified, mainly using the Lyapunov exponent method, the correlation dimension method and the kolmogorov entropy method. Secondly, the hybrid model is established for dam deformation forecasting. Taking SVM as the core, the deformation time series is reconstructed in phase space to determine the input variables of SVM, and the GWO algorithm is improved to realize the optimization of SVM parameters. Prior to this, the effectiveness of DEGWO algorithm based on the fusion of the difference evolution (DE) and GWO algorithm has been verified by 15 sets of test functions in CEC 2005. Finally, take the actual monitoring displacement of Jinping I super-high arch dam as examples. The engineering application examples show that the PSR-SVM-DEGWO model established performs better in terms of fitting and prediction accuracy compared with existing models.
Dams and Floods F. Lempérière
Engineering (Beijing, China),
02/2017, Volume:
3, Issue:
1
Journal Article
Peer reviewed
Open access
The possible mitigation of floods by dams and the risk to dams from floods are key problems. The People＇s Republic of China is now leading world dam construction with great success and efficiency. ...This paper is devoted to relevant experiences from other countries, with a particular focus on lessons from accidents over the past two centuries and on new solutions. Accidents from floods are analyzed according to the dam＇s height, storage, dam material, and spillway data. Most of the huge accidents that have been reported occurred for embankments storing over 10 hm3. New solutions appear promising for both dam safety and flood mitigation.
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