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How does mine tailings slurry solids concentration affect stability of dam embankment slope?
... However, physical models cannot automatically calculate thresholds from longterm monitoring data, so they are incompetent in automatic warning of creeping and accelerating stages. The typical physical-mechanical models mainly consist of limit equilibrium (Gowhar et al., 2023;Tesfaye et al., 2023), fine element (Otieno & Shukla, 2024;Wijesinghe et al., 2022), strength reduction (Meko et al., 2023;Rafiei et al., 2023), distinct element (Harnett et al., 2023;Jensen & Moore, 2023), stability index mapping (Memarian et al., 2023), and combination of slope and hydrological models (Chansorn et al., 2023;Mauri et al., 2022;Petpongpan et al., 2021). ...
Automatic deformation forecast and warning of a catastrophic landslide can effectively avoid significant casualties and economic losses. However, currently it has not come to a comprehensive forecast framework covering all the deformation stages of a landslide. Moreover, landslide deformation prediction possesses high error and false alarm rates. This work suggests a novel integrated framework of landslide deformation forecast and warning by coupling machine learning and physical models. The framework can relatively accurately predict all the deformation stages from creeping deformation to critical sliding and features 4 advantages. (a) The forecast indices are established by combining deformation and disaster‐triggering characteristics to improve the prediction accuracy. (b) It leverages the advantage of C5.0 decision tree algorithm in knowledge interpretability to automatically extract deformation forecast criteria. (c) It capitalizes on the precision superiority of a graph convolutional network in time‐series data learning to predict the four deformation stages from creeping deformation to rapidly accelerated deformation. (d) It utilizes the physical and mechanical bases of Morgenstern‐Price method to forecast the critical sliding stage. Zhujiatang Landslide is a large‐scale deep‐seated soil landslide with significant deformation. It is selected as a case study because it has endangered 1,131 persons and may cause a direct financial loss of 100 million RMB. The validating and predicting Accuracy values attain 97.39% and 95.72%, respectively, and the Kappa values reach 0.91 and 0.93, respectively. The landslide will run out when it suffers from a rainstorm with cumulative rainfall of 79.57 mm and an earthquake with a horizontal coefficient of 0.04.
The conventional disposal of slurried tailings in a tailings storage facility (TSF) leads to the formation of a beach, on which the tailings sort hydraulically, settle, consolidate, and desiccate upon exposure. Basic geotechnical testing, such as specific gravity, Atterberg limits, and particle size distribution, found that there was no particular trend of changes in the tailings properties down the beach. The settled sediment found in a settling test was slurry-like and unsuitable for conventional oedometer testing. Constant rate of loading (CRL) consolidation testing is more representative of the continuous disposal of tailings slurry than conventional step loading. Consolidation testing in a slurry consolidometer was conducted and captured from a slurry-like to soil-like state. A slow rate of loading increased the test time, while a too quick rate of loading built up very high excess PWP. The test results showed different stages of consolidation, depending on excess PWP development and dissipation, and applied stress.
Tailings' Dams are mining waste impounding structures. They differ from conventional dams in purpose, design and operation. Percentage wise their failures are higher and posing considerably more safety concerns, causing long lasting devastation on communities, environment, and animal and plant ecosystem. Two basic types of embankment tailings structures are used for tailings impoundments; the Retention Dams and the Raised Dams. Retention dams are built in one operation to a full height, while construction of Raised Dams is a continuous process lasting for the whole useful life of the mine. Raised Dams are favored over Retention dams as they can be enlarged and expanded as the extraction works continue with time. Raised embankment dams themselves can be of three alternative designs according to the method used in construction; the Downstream, Upstream and Centerline structures. This designates the direction in which the embankment crest moves in relation to the initial embankment at the base as successive lifts are added. Resulting from the used method of tailings weight disposition, the Upstream Raised Dams are the least safe in earthquake prone areas as compared to the other two types due to its higher possibility of liquefaction, so they are not favored in highly seismic areas. The disadvantage of Downstream Raised Dams is their use of larger land areas. Centerline Raised Dams are a compromise between the other two. Tailing Dams failure may occur due to: dam instability, overtopping, internal erosion, or combination of these. Instability can result from faulty design and/ or faulty tailings deposition method. Internal erosion can follow saturation of the fill due to fast rate of work and close proximity of the water pond to the dyke combined with
The volume change and shear strength behaviour of tailings slurry with the changes in gravimetric moisture content is important to effectively utilise the storage volume and analysis of dam failure potential. Consolidation testing of tailings from a slurry-like to soil-like state is a critical task, and conventional consolidation apparatus does not have the capability of doing such testing, as the tailings slurries contain high water content. Settling tests conducted on slurries having a 25% solids concentration showed very low efficiency; final sediment was still slurry-like. An intrinsic point was identified based on pore water pressure dissipation during consolidation tests in a slurry consolidometer that can define two states of the tailings i.e. slurry-like and soil-like. In the slurry-like state, the volume change was greater for Slurry 2 than Slurry 1, while the inverse was observed in the soil-like state. The evolution of peak vane shear strength with the changes in moisture content was almost similar for both samples and obeyed the power function. Regression models have been developed and validated to predict the shear strength of materials at any gravimetric moisture content or void ratio.
In order to understand permeability behavior of high-moisture content dredged slurry in a storage yard, this article utilizes two modified oedometers to conduct consolidation and permeation tests on various kinds of high-moisture content dredged slurries in China. Experimental results show that although initial moisture content exerts a significant impact on the compression properties of dredged slurries, its impact on permeability property is relatively small, and the permeability coefficient has a one-to-one correspondence with the void ratio. In the coordinate system of e ∼ logk, the permeability coefficient of dredged slurry shows a nonlinear variance with void ratio. The permeability coefficient variability index C k is mainly distributed within 0.3 ∼ 0.7e and approximates to 0.5e. But in the coordinate system of loge ∼ logk, the permeability coefficient of dredged slurry shows a linear variance with the void ratio. Lastly, a e ∼ k quantitative method adapted to high-moisture content dredged slurry is proposed based on the normalized parameter e/e L .
The large volumes and the low settling rates of slurry tailings entail some of the most challenging issues faced by the geotechnical engineering community such as the design, construction, and maintenance of large waste containment facilities. The recent shift from conventional tailings disposal to thickened tailings discharge requires special attention right at the conceptual level. The fundamental concepts of hindered sedimentation (Pane and Schiffman 1985) and large-strain consolidation (Been and Sills 1981) are generally understood when considered separately. A more critical issue is to understand the transition from sedimentation to consolidation, that is, at what void ratio a slurry settling under gravity becomes a soil possessing effective stresses. A clear answer of this question is crucial in selecting appropriate synthetic polymers for optimum thickening and in developing tailings deposition schedules in the field. Based on two case studies from Canada and South America, this article tries to help understand the transition from sedimentation to consolidation.
The majority of slope stability analyses performed in practice still use traditional limit equilibrium approaches involving methods of slices that have remained essentially unchanged for decades. This was not the outcome envisaged when Whitman & Bailey (1967) set criteria for the then emerging methods to become readily accessible to all engineers. The finite element method represents a powerful alternative approach for slope stability analysis which is accurate, versatile and requires fewer a priori assumptions, especially, regarding the failure mechanism. Slope failure in the finite element model occurs `naturally' through the zones in which the shear strength of the soil is insufficient to resist the shear stresses. The paper describes several examples of finite element slope stability analysis with comparison against other solution methods, including the influence of a free surface on slope and dam stability. Graphical output is included to illustrate deformations and mechanisms of failure. It is argued that the finite element method of slope stability analysis is a more powerful alternative to traditional limit equilibrium methods and its widespread use should now be standard in geotechnical practice.
The stability of tailings dams has drawn much attention over the past few decades as a significant number of tailings dam failures have been recorded worldwide. The present study focuses on the investigation of the behavior and the stability of this kind of earth structure under static and dynamic loading. To accomplish this task, elaborate two-dimensional numerical simulations are conducted, utilizing two widely used geotechnical finite element codes. Initially, numerical analyses are performed for three typical types of tailings dams to obtain the potential modes of slope instability by determining the corresponding factors of safety under static conditions. Subsequently the dynamic distress of tailings dams is thoroughly investigated in terms of inertial accelerations developed. Based on the models examined under static loading, dynamic analyses are performed to examine the effects of local site conditions on the seismic response of tailings dams, and therefore on their inertial distress. Emphasis is given to the special characteristics of the ground motion, whereas the material nonlinearity of both soil and tailings is taken into account by an efficient equivalent-linear procedure.
Mine tailings dams are surface impoundment structures consisting of raised embankments that are built to contain mine tailings and mill effluents. In the past, many failures of these iron ore mine tailings storage facilities/dams have been reported worldwide in different forms. In this paper, an attempt has been made to review the failure modes, mechanisms and possible solutions to enhance the stability and safety of iron ore tailings dams. A comprehensive investigation has been carried out on 16 failure cases of such dams that were reported from 1917 to the current period. Additionally, mineralogy of iron ore tailings has been provided. The analysis of the past failures shows that most failures took place as a result of slope instability, overtopping, liquefaction-related instability, foundation movement and some form of structural failure. It has been found that 31.25% of iron ore mine tailings dams collapsed due to slope instability, 18.75% due to overtopping, 6.25% due to liquefaction-related instabilities, 6.25% due to foundation failure, 6.25% due to erosion, and 6.25% due to structural failure. In 25% of the failure cases, the causes have been unknown. An attempt is also made here to present prevention and remediation measures for avoiding failures and the associated negative environmental impacts in future.
Mine tailings stored in the tailings storage facility (TSF) are normally loose and failure-prone for several reasons, such as liquefaction, erosion, overtopping, piping, high excess pore water pressure (PWP). The investigation of mechanical behaviour of tailings material is essential for engineering design and safety evaluation of the TSF during mining operations, closure and rehabilitation. As such, laboratory compaction, consolidation and direct shear strength experiments are carried out on three different fine-grained mine tailings, named coal tailings (CT), red mud (RM) and gold tailings (GT). Compared to CT and RM, GT showed higher dry density at the optimum moisture content (OMC) and lower compressibility. The permeability of GT is similar to RM but much higher than that of CT. CT and GT showed the highest cohesion and angle of internal friction, respectively, among the tested materials. The direct shear test among all the methods used provided the highest dry density and lowest void ratio. The final state parameters obtained in compaction, consolidation and direct shear tests are critically compared, which is the novelty of this study. This research explored useful information on the geotechnical properties of different tailings that can help mining operators and researchers to effectively design and manage the tailings in the TSF.
This book integrates the physical processes of dam breaching and the mathematical aspects of risk assessment in a concise manner: The first book that introduces the causes, processes and consequences of dam failures. Integrates the physical processes of dam breaching and the mathematical aspects of risk assessment in a concise manner. Emphasizes integrating theory and practice to better demonstrate the application of risk assessment and decision methodologies to real cases. Intends to formulate dam-breaching emergency management steps in a scientific structure. © 2016 John Wiley & Sons Singapore Pte. Ltd. All Rights Reserved.
This chapter defines some fundamental quantities that are used to describe the relative amounts of the three phases that comprise soils. Knowledge of the associated “arithmetic” of soil mechanics forms a basis for most calculations performed in Geotechnical Engineering.
This book describes the processes by which tailings are produced, and why the solids must be separated from them. The usual method is by allowing the tailings slurries to settle in ponds, retained by temporary dams. These dams are described in all their aspects, both the theoretical behaviour of fluids in the ponds, and engineering aspects of their placing, design and construction, and the behaviour and prevention of seepage. (U.K.)
An analysis of the conditions that led to the failure of the Aznalcollar dam is made in the paper. Pore water pressures prevailing in the foundation clay at the time of the failure have been established on the basis of piezometric observations made after the failure. A simplified consolidation analysis is first presented to interpret pore water pressure generation and dissipation and to evaluate the evolution of shear stresses along the potential failure plane. Both limit equilibrium and finite element analysis are used to back-analyse the failure and to derive representative strength parameters along the failure surface. Three-dimensional effects introduced by the layered nature of the foundation clay are then described. They provide an explanation for the location of the slide, which affected only the south-eastern portion of the embankment. The failure is examined in the final part of the paper from the perspective offered by the current knowledge of the strength behaviour of brittle clays. The significance of progressive failure is discussed, together with other factors that played a significant role in this case: the homogeneous nature and very low permeability of the foundation clay and the natural state of the clay, probably affected by some initial damage, which reduced the available strength along bedding planes.
Coarse and fine refuse is produced by various coal processing equipment. The relatively wet fine tailings have limited use in construction activities and they are generally pumped as slurries into tailings ponds. The coarse rejects have a greater engineering applicability and are utilized in the construction of tailings dams and mine access roads as well as for landfill and ballast. This study investigates the fundamental engineering properties of blended tailings, whereby appropriate fractions of flotation tailings are mixed with cyclone rejects to produce an acceptable construction or rehabilitation fill. In particular, a practical procedure to optimize the blended ratios, is proposed on the basis of fundamental geotechnical testing. The applications of relevent tests are described, including Proctor compaction, California Bearing Ratios, triaxial and consolidation tests. The results confirm that blending of fines with coarse rejects enables enhanced dry densities associated with reduced permeabilities, higher shear and compressive strengths, lower consolidation settlements and increased bearing capacities. The addition of a small quantity of cement (2-5%) further improves the engineering properties of the blended matrix. -from Author
The upstream method is a popular method for raising tailings dams. Currently in China there are more than 12,000 tailings impoundments and almost 95% of them use the upstream method for the construction of the dam. Statistical data has shown that the tailings impoundment is one of the main sources of risk in the mining industry. Failures of tailings impoundments have resulted in the loss of many lives, considerable property damage, and irreversible pollution in downstream areas. Therefore, the safety of tailings management facilities has been of increasing concern to governments and local communities. The management of a conventional tailings storage facility requires the maintenance of a high level of structural stability. Therefore, according to the relevant mine Acts, the mine operators are required to conduct stability analyses for all types of tailings facilities, whether they are new, active, or decommissioned. For the stability analysis of tailings dams, the accurate profile of the tailings dam is very important. The profiles are easily obtained for both active and decommissioned tailings facilities because their data can be collected through field investigations. However, collecting basic data from newly constructed tailings facilities is difficult. In this paper, a laboratory physical model test has been performed. The construction process for new tailings impoundment has been physically simulated in the laboratory, where the tailings particle composition and distribution below a beach, the change of phreatic surface of the dam, and the engineering properties of the tailings of the dam profiles have been measured. A new tailings facility, Yangtianqin tailings impoundment, owned by Tongchang copper mine of Yuxi Mine Co., was used as a case study to illustrate the physical modeling of the tailings dam. In the model test, the geometrical model of pond area was constructed according to the scale factor, λL, of 1:200 (model:prototype), and the tailings discharge system was also established, the tailings slurry then being discharged based on the design data. Finally, on the basis of the model test results on profiles, the stability analysis of the tailings dam at different heights was conducted under different conditions. The model test results and stability analysis show that the height of the tailings dam should be less than that originally planned. The original design of Yangtianqing tailings impoundment should therefore be revised for the safety of the tailings impoundment.
It is common for the rate of seepage through a tailings embankment to be estimated on the basis of a conventional flow net analysis assuming steady seepage conditions. Moreover an impervious seal is generally recommended against the upstream face of the dam to minimize seepage flow through the sand embankment. This study shows that, due to rapid rates of placing, slimes can exist in an under-consolidated state. Field measurements are cited in support of the theory and the implications of under-consolidated slimes in the pond are discussed in detail. Procedures to analyse the utility of an upstream seal are also discussed and design examples reflecting actual operating conditions are given.
Waste management issue in mining industry has become increasingly important. In this regard, construction of tailings dams
plays a major role. Most of the tailings dams require some kinds of remedial actions during their operational lifetime, among
which heightening is the most common. In the first stage of the remedial provisions for Sarcheshmeh Copper Complex tailings
dam in Iran, it has been decided to use hydrocyclone method to provide suitable construction material due to the high cost
associated with using borrow materials for heightening of the dam. To undertake this project a series of laboratory experiments
was performed to determine the copper ‘original tailings’ and ‘cycloned materials’ geotechnical characteristics to evaluate
the applicability of the cycloned materials for construction purposes. Different laboratory experiments were conducted to
determine the grain-size distribution, Atterberg limits, specific gravity, maximum density, shear strength parameters, consolidation
coefficient, and hydraulic conductivity. The results were compared with those of similar mines to check whether they follow
the trends observed in other copper tailing materials elsewhere. Variation of the cohesion and internal friction angle versus
different compaction ratios were studied in order to determine realistic shear strength parameters for tailing dam stability
analysis. In this study, using oedometer test, a mild linear relation between void ratio and the consolidation coefficient
has been found for tailings materials. By considering the effects of void ratio and weight of passing sieve #200 materials,
a new relationship is proposed that can be used for estimating the copper slimes hydraulic conductivity in seepage analysis
of tailings dams.
How the dilatancy of soils affects their behaviour. The written version of an invited lecture delivered at the tenth European Conference on Soil Mechanics and Foundation Engineering
- G T Houlsby
- Houlsby G.T.