Field evidence of resuspension in a mine tailings pond

2001 ◽  
Vol 38 (4) ◽  
pp. 796-808 ◽  
Author(s):  
Celestina Adu-Wusu ◽  
Ernest K Yanful ◽  
Mohammed H Mian
Keyword(s):  
Shear Stress ◽  
Mine Tailings ◽  
Critical Shear Stress ◽  
Field Measurements ◽  
Shear Stresses ◽  
Wind Speeds ◽  
Tailings Pond ◽  
Field Evidence ◽  
Water Cover ◽  
Solubility Of Oxygen

Flooding of tailings under shallow water covers is an effective method of decommissioning potentially acid generating mine tailings. The low diffusivity and solubility of oxygen in water are attractive features of this technology. However, wind-induced waves can resuspend flooded tailings and expose them to greater contact with dissolved oxygen, thereby increasing the potential for oxidation and acid generation. Field measurements of wind activity and waves under different water cover depths and associated resuspension for a mine tailings pond in Ontario are presented and discussed. The results show that wind speeds greater than 8 m/s above water covers that are shallower than 1 m create waves of height greater than 10 cm and bottom shear stresses greater than 0.2 Pa. Under these conditions the critical shear stress of the mine tailings was exceeded, resulting in erosion and subsequent resuspension.Key words: mine tailings, water cover, wind-induced waves, resuspension, wind speed, shear stress.

Measuring the onset of mine tailings erosion

2007 ◽  
Vol 44 (4) ◽  
pp. 473-489 ◽  
Author(s):  
M Haneef-Mian ◽  
Ernest K Yanful ◽  
Robert Martinuzzi
Keyword(s):  
Shear Stress ◽  
Power Law ◽  
Mine Tailings ◽  
Laser Doppler Anemometry ◽  
Critical Shear Stress ◽  
Laser Doppler ◽  
Shear Stresses ◽  
Cohesive Sediments ◽  
Fine Grained ◽  
Power Law Equation

The present study gives details of a methodology for estimating the critical shear stress for erosion of mine tailings and other naturally occurring cohesive sediments. Erosion of a cohesive sediments bed occurs when the critical shear stress is exceeded to break the interparticle bond. Experiments were conducted in a 30 cm diameter laboratory column and calibrated using laser Doppler anemometry. The results showed that the erosion pattern of mine tailings particles was similar to those of fine-grained cohesive sediments. A power-law relation of the form E = α[(τ – τcr)/τcr]n is suggested for mine tailings, where E is the erosion rate, α is a coefficient, τ is the shear stress, τcr is the critical shear stress, and n is an exponent. The computed values of α, n, and τcr in the power-law equation were found to be comparable to values derived from experiments in a rotating circular flume. The derived expression for rate of erosion may be incorporated in resuspension and transport models for fine mine tailings of a similar nature.Key words: mine tailings, laser Doppler velocimetry, wall shear stresses, critical shear stress for erosion, erosion – shear stress relationship.

Behavior of mine tailings under cyclic hydraulic loading

2011 ◽  
Vol 38 (2) ◽  
pp. 131-140 ◽  
Author(s):  
Africa M. Geremew ◽  
Ernest K. Yanful
Keyword(s):  
Shear Stress ◽  
Shallow Water ◽  
Mine Tailings ◽  
Critical Shear Stress ◽  
Pressure Change ◽  
Visual Observation ◽  
Laser Doppler Velocimeter ◽  
Surface Erosion ◽  
Water Cover ◽  
Erosion Equation

Shallow water cover is one of the most effective methods of managing sulfide-bearing reactive mine tailings. Unless sufficient water cover depth is provided, surface erosion by wind-induced waves and pressure-driven currents can re-suspend the tailings and expose them to dissolved oxygen and affect the quality of the water cover. The present study gives a simple approach for the estimation of the critical shear stress for surface erosion of mine tailings and cohesive sediments under shallow water cover. Erosion tests were carried out in a Plexiglas laboratory annular column on mine tailings and sediments under a 50 cm water cover. The annular column was 30 cm in diameter, 120 cm in height and had a 9 cm annular flow width. Shear stress was introduced through a motor driven Teflon stirrer to investigate the initiation of motion and subsequent re-suspension of newly deposited mine tailings and sediments. The velocity field and the pressure change in the boundary layer were measured by laser Doppler velocimeter (LDV) and Preston tube, respectively. The ranges of critical shear stress for the tailings and sediments were estimated by the LDV and Preston tube measurements and visual observation. The results showed that the erosion behavior of most of the mine tailings can be explained by a power law erosion equation.

A design approach for selecting the optimum water cover depth for subaqueous disposal of sulfide mine tailings

2005 ◽  
Vol 42 (1) ◽  
pp. 207-228 ◽  
Author(s):  
Mustafa A Samad ◽  
Ernest K Yanful
Keyword(s):  
Shear Stress ◽  
Mine Tailings ◽  
Wind Waves ◽  
Sediment Resuspension ◽  
Critical Shear Stress ◽  
Linear Wave ◽  
Cover Depth ◽  
Water Cover ◽  
The Impact

The use of shallow water covers to flood reactive mine tailings is one of the most effective and common methods of managing sulfide-rich reactive mine tailings in temperate climates. One of the aspects critical to the success of subaqueous tailings disposal is the water depth required in the pond to maintain desirable water quality. Wind waves and associated pressure-driven currents could resuspend the tailings, which might result in increased oxidation and compromise the quality of the water cover. Although existing methodologies for water cover design are based on eliminating tailings resuspension, sediment-trap data from several sites in Canada still indicate resuspension in most of the ponds. In the present paper, a design methodology is proposed for optimizing the water cover depth, allowing sediment resuspension within regulatory limits. The method uses linear wave theory and countercurrent flow profiles to obtain the total bottom shear stress, which is then compared with the critical shear stress of the tailings to predict the onset of erosion and resuspension and to compute the resulting mass of suspended tailings. Application of the methodology to a tailings pond in British Columbia, Canada, indicates that although a maximum water cover depth of 2.5 m is necessary to eliminate tailings resuspension, a maximum depth of 1.5 m could still be used, as the resulting concentration of suspended tailings remains within the regulatory limit. The methodology also provides an estimate of the impact of resuspension-induced oxidation on the quality of the water cover above the tailings, such as sulfate production.Key words: mine tailings, water cover, wind waves, countercurrent flows, shear stress, resuspension.

Role of fines on cohesive behavior of mine tailings inferred from critical shear stress

2011 ◽  
Vol 48 (4) ◽  
pp. 568-582 ◽  
Author(s):  
Africa M. Geremew ◽  
Ernest K. Yanful
Keyword(s):  
Shear Stress ◽  
Mine Tailings ◽  
Erosion Rate ◽  
Empirical Relation ◽  
Critical Shear Stress ◽  
Pressure Change ◽  
Laser Doppler Velocimeter ◽  
Shear Stresses ◽  
Boundary Shear ◽  
Boundary Shear Stress

The significance of fines on the cohesive behavior of mine tailings has been investigated by examining the incipient motion of the tailings. Sixteen laboratory experiments were performed in a Plexiglas laboratory annular column on re-constituted mine tailings under a 50 cm water cover. Re-suspension was produced by a Teflon stirrer and the velocity field in the column was characterized using a laser Doppler velocimeter (LDV). The pressure change in the boundary layer was also measured with a Preston tube. It was observed that the nondimensional critical shear stresses showed deviation from those of the noncohesive model results at a fines content greater than 50%–55%. An empirical relation that shows the relation between the boundary shear stress deviation and the percent fines in the tailings was proposed. Regression analysis of the experimental results showed that a power law relationship could reasonably be used to describe the relation between the measured nondimensional excess bed shear stress and the erosion rate. It is proposed that the value of β (the erosion rate constant) could be taken as 1 for mine tailings that show cohesive behavior.

Development of a Three-Dimensional Iterative Methodology Using a Commercial CFD Code for Flow Scouring Around Bridge Piers

2012 ◽  
Author(s):  
Phani Ganesh Elapolu ◽  
Pradip Majumdar ◽  
Steven A. Lottes ◽  
Milivoje Kostic
Keyword(s):  
Shear Stress ◽  
Three Dimensional ◽  
Critical Shear Stress ◽  
Shear Stresses ◽  
Computational Domain ◽  
Time Step ◽  
Mesh Morphing ◽  
River Bed ◽  
Scour Hole ◽  
The Stability

One of the major concerns affecting the safety of bridges with foundation supports in river-beds is the scouring of river-bed material from bridge supports during floods. Scour is the engineering term for the erosion caused by water around bridge elements such as piers, monopiles, or abutments. Scour holes around a monopile can jeopardize the stability of the whole structure and will require deeper piling or local armoring of the river-bed. About 500,000 bridges in the National Bridge Registry are over waterways. Many of these are considered as vulnerable to scour, about five percent are classified as scour critical, and over the last 30 years bridge failures caused by foundation scour have averaged about one every two weeks. Therefore it is of great importance to predict the correct scour development for a given bridge and flood conditions. Apart from saving time and money, integrity of bridges are important in ensuring public safety. Recent advances in computing boundary motion in combination with mesh morphing to maintain mesh quality in computational fluid dynamic analysis can be applied to predict the scour hole development, analyze the local scour phenomenon, and predict the scour hole shape and size around a pier. The main objective of the present study was to develop and implement a three dimensional iterative procedure to predict the scour hole formation around a cylindrical pier using the mesh morphing capabilities in the STARCCM+ commercial CFD code. A computational methodology has been developed using Python and Java Macros and implemented using a Bash script on a LINUX high performance computer cluster. An implicit unsteady approach was used to obtain the bed shear stresses. The mesh was iteratively deformed towards the equilibrium scour position based on the excess shear stress above the critical shear stress (supercritical shear stress). The model solves the flow field using Reynolds Averaged Navier-Stokes (RANS) equations, and the standard k–ε turbulence model. The iterative process involves stretching (morphing) a meshed domain after every time step, away from the bottom where scouring flow parameters are supercritical, and remeshing the relevant computational domain after a certain number of time steps when the morphed mesh compromises the stability of further simulation. The simulation model was validated by comparing results with limited experimental data available in the literature.

Initiation of motion conditions for shale sediments

1983 ◽  
Vol 10 (3) ◽  
pp. 549-554 ◽  
Author(s):  
L. Magalhaes ◽  
T. S. Chau
Keyword(s):  
Shear Stress ◽  
Critical Shear Stress ◽  
Shear Stresses ◽  
Single Particles ◽  
Channel Stability ◽  
High Lift ◽  
Flume Tests ◽  
Load Transport ◽  
Bed Load Transport ◽  
Bed Material

Critical shear stresses for erosion of alluvial shale particles were investigated in a laboratory flume. Tests in the incipient motion conditions of individual particles showed that entrainment of shale bed particles takes place at mean shear stress values 40–50% smaller than other types of non-cohesive and coarse granular material. The low density and platy shape of the shale particles may induce high lift forces, which would account for a decrease in the resistance to erosion of shale channels and greater rates of bed-load transport. Keywords: channel stability, critical shear stress, flume tests, initiation of motion, shale gravels, single particles, weak bed material movement.

Critical Shear Stresses of Sunken Oils

2014 ◽  
Vol 2014 (1) ◽  
pp. 300241
Author(s):  
Charles Watkins ◽  
Olivia Jobin ◽  
Nancy Kinner ◽  
Thomas Ballestero ◽  
Neil W. Thomas ◽  
...  
Keyword(s):  
Shear Stress ◽  
Three Dimensional ◽  
Critical Shear Stress ◽  
Water Current ◽  
Shear Stresses ◽  
High Definition ◽  
Annular Flume ◽  
The University ◽  
University Of New Hampshire ◽  
Sunken Oil

As observed in several recent cases (e.g., DBL-152, Enbridge-Kalamazoo), under certain circumstances, spilled oil can sink to the bottom of a water body. Once on the bottom, the oil can move or even remobilize into the water column. The critical shear stress (CSS) is used to accurately predict the movement of sunken oil along and off the bottom. Unfortunately, shear stress has only been measured for one sunken oil (Hibernian Crude API = 34). The Coastal Response Research Center (CRRC) at the University of New Hampshire (UNH) has an annular flume equipped with high-definition cameras and an acoustic velocimeter that can be used to estimate CSS by measuring the instantaneous, three-dimensional water current velocities at which sunken oils move and erode as visible oil droplets. The results reported are for an Alberta bitumen, tested at temperatures between 5° and 28°C in freshwater.

Erosion characteristics and stochastic nature of bed shear stress in underwater mine tailings

2017 ◽  
Vol 44 (6) ◽  
pp. 426-440 ◽  
Author(s):  
Africa M. Geremew
Keyword(s):  
Shear Stress ◽  
Mine Tailings ◽  
Pore Water Pressure ◽  
Water Pressure ◽  
Critical Shear Stress ◽  
Pressure Change ◽  
Rayleigh Distribution ◽  
Surface Erosion ◽  
Bed Shear Stress ◽  
Stochastic Nature

The erosion of mine tailings was investigated by examining the physical processes during the initiation of motion of the tailings. Erosion experiments were conducted on mine tailings samples and natural soils in a Plexiglas laboratory annular column under 50 cm water cover. Resuspension was introduced with a Teflon stirrer and the bed shear stress was estimated from the measured near-bed velocity field and the pressure change in the boundary layer. Two modes of initiation of motion of cohesive mine tailings that showed cohesive behaviour was noticed: pitting erosion and line erosion and the modes of initiation of motion changed mainly with percentage of fines. At incipient motion of the tailings that showed cohesive behaviour, the pore water pressure distribution showed a relative sudden peak and a decline when the aggregated tailings burst. A four order of magnitude difference was observed between the undrained shear strength and critical shear stress for surface erosion of the tailings. The stochastic nature of the bed shear stress was explained by the Rayleigh distribution that provides an approach for correcting the critical shear stress estimated from the near-bed velocity. This correction is necessary to achieve a conservative estimate of the critical shear stress for design purposes.

A 3D Finite Element Study of Fatigue Life Dispersion in Rolling Line Contacts

2011 ◽  
Vol 133 (4) ◽  
Author(s):  
Nick Weinzapfel ◽  
Farshid Sadeghi ◽  
Vasilios Bakolas ◽  
Alexander Liebel
Keyword(s):  
Finite Element ◽  
Shear Stress ◽  
Material Properties ◽  
Rolling Contact Fatigue ◽  
Contact Fatigue ◽  
Critical Shear Stress ◽  
Rolling Contact ◽  
Shear Stresses ◽  
Rolling Element Bearings ◽  
Rolling Element

Rolling contact fatigue of rolling element bearings is a statistical phenomenon that is strongly affected by the heterogeneous nature of the material microstructure. Heterogeneity in the microstructure is accompanied by randomly distributed weak points in the material that lead to scatter in the fatigue lives of an otherwise identical lot of rolling element bearings. Many life models for rolling contact fatigue are empirical and rely upon correlation with fatigue test data to characterize the dispersion of fatigue lives. Recently developed computational models of rolling contact fatigue bypass this requirement by explicitly considering the microstructure as a source of the variability. This work utilizes a similar approach but extends the analysis into a 3D framework. The bearing steel microstructure is modeled as randomly generated Voronoi tessellations wherein each cell represents a material grain and the boundaries between them constitute the weak planes in the material. Fatigue cracks initiate on the weak planes where oscillating shear stresses are the strongest. Finite element analysis is performed to determine the magnitude of the critical shear stress range and the depth where it occurs. These quantities exhibit random variation due to the microstructure topology which in turn results in scatter in the predicted fatigue lives. The model is used to assess the influence of (1) topological randomness in the microstructure, (2) heterogeneity in the distribution of material properties, and (3) the presence of inherent material flaws on relative fatigue lives. Neither topological randomness nor heterogeneous material properties alone account for the dispersion seen in actual bearing fatigue tests. However, a combination of both or the consideration of material flaws brings the model’s predictions within empirically observed bounds. Examination of the critical shear stress ranges with respect to the grain boundaries where they occur reveals the orientation of weak planes most prone to failure in a three-dimensional sense that was not possible with previous models.

Computational Fluid Dynamics Characterization of a Bioreactor Mixing Device for the Animal Cell Culture

2011 ◽  
Vol 6 (1) ◽  
Author(s):  
Valérie Gisèle Gelbgras ◽  
Christophe E Wylock ◽  
Jean-Christophe Drugmand ◽  
Benoît Haut
Keyword(s):  
Fluid Dynamics ◽  
Cell Culture ◽  
Computational Fluid Dynamics ◽  
Shear Stress ◽  
Cell Viability ◽  
Animal Cell ◽  
Scale Up ◽  
Critical Shear Stress ◽  
Shear Stresses ◽  
A Cell

During a cell culture in a bioreactor, the cells are exposed to the shear stresses mainly generated in the culture medium by the mixing device. Beyond a critical shear stress, this exposition induces cell damages. Therefore, the limitation of the shear stress is an important criterion for the design of bioreactors. An accurate modeling of the flow and the induced shear stresses in the medium is a tool to achieve an effective design of a bioreactor. In this work, a new design of a mixing device is considered. The aims of this work are to develop a methodology to study the flow and the induced shear stresses in the device, to study and to model the relation between the flow, the induced shear stresses and the cell viability, to use the developed model as an optimization tool, and to study the design of the bioreactor mixing device and its scale-up. In a first step, the flow and the induced shear stresses in the device are simulated by Computational Fluid Dynamics. In a second step, the model of the influence of the flow and the induced shear stresses on the cell viability is established by a comparison between the computed flow and the induced shear stresses and experimental measurements of cellular viabilities for different impeller rotation speeds. Finally, the influence of another design of the mixing device on the cell viability is studied.

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