3-slurry ponds, ash, tailings and dredged sediments

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INTRODUCTIONThermal power is the chief source of energy in Indiaand accounts for nearly 70 percent for total energyproduction. Indian coal used in thermal power plants(TPP) are having large impurities and hence resulting

ash content after combustion is very high (40-50%).Coal ash is the ash produced by burning of pulverizedcoal in TPP that gets collected at the bottom offurnace as well as in electrostatic precipitators. Thecoal ash generated from all the existing thermal powerplants is over 100 million tones per year (Gulhati &Datta, 2005). The percentage utilization of coal ashin various construction activities is still limited inIndia compared to other countries. In view of highash content and low percentage utilization, most ofthe fly ash has to be suitably disposed off on land bycreating an engineered ash pond to take care ofenvironmental concerns. The fly ash as well asbottom ash produced by the plant is generallydisposed of in an ash pond in the form of slurry orsometimes (seldom) in dry state. Fly ash and bottomash from the power plant is mixed with water in aratio varying from 1 part ash and 6 to 10 parts ofwater. The slurry is then pumped upto the ash pond

which are located within few kilometers distance from

Raising of Dykes of Ash Slurry Pond - ACase Study

S.K SinghPEC University of Technology, Chandigarh, India ( [email protected])

Manoj DattaPEC University of Technology, Chandigarh, India (director @pec.ac.in)

ABSTRACT The present paper deals with design of raising of dykes for ash pond by upstream method usingash as construction material with suitable protection and drainage measures for a Thermal Power Plant inPunjab (India). A site investigation was carried out at the pond and dyke area through SPT and undisturbed

sampling. Stability analyses were also carried out. Minimum factor of safety for the existing dyke (2.5 H : 1 V)without any consideration of seepage is observed to be 1.5 and in the case of ponding of water (seepagecondition) FOS drops down below 1.0. All the design details including remedial measures are presented in the

paper.

the power plant. Due to land scarcity, the dykes othe ash pond are raised once it is filled with ash to takcare of further load of generated ash. Typically, asgenerated from 500 MW thermal power plants gefilled to 10 m height over a period of 5 years (Gandhi

al., 2000). Therefore, ash ponds are constructed istages and the height of dyke of the ash ponds arrequired to be raised time to time as and when the aslevel reaches nearly top of existing dyke. The raisinof dyke at one time may vary from 3 to 5 m.The present paper deals with the case study of raisinof ash dykes by 3 to 6 m by upstream method forthermal power plant (4x410 MW) located in Punjastate (India). The ash pond occupies a very largarea of 847 acres (3.43 million sq m). Starter dykes oheight 3 m were constructed all along the perimeteof the ash pond in the beginning. These dykes werraised by 3 m for the first time in the year 1997 ansubsequently some part of the dykes were raisefurther by 3 m in the year 2004. Ash level in the ponreached top level of the dyke in the year 200requiring further raising of the dykes to prevent asslurry from overflowing over the dykes Thereforthe case was considered for the raising of dykes by

m (3

rd

raising) and in some stretch by 6 m (2

nd

raising


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504 6th International Congress on Environmental Geotechnics, 2010, New Delhi, India

OBSERVATIONS FROM SITE VISITThe site visit was undertaken during 2009 and thefollowing observations were noted:The ash pond (Photo 1) occupies a very large area(3.43 million sq m).

(a) No decanting arrangement for slurry water

was available.(b) Slurry water was observed to dry out due

to evaporation and downward flow.(c) At most places the pond was dry.(d) No seepage was observed on the

downstream side of the dykes.(e) Downstream slope was covered with shrubs

and access to the toe was difficult.(f) No toe drain was provided.(g) No failure of dyke had been reported in the

past.(h) The stability analysis should be carried out

for dry condition and seepage condition both,since water may be ponded behind the dykedue to inadequate drainage facility.

Photo 1 Photograph of Ash Pond

SITE INVESTIGATION

A site investigation programme was drawn up withthe following objectives: To determine the final cross section of

existing dykes. To ascertain the depth of ash at various

locations within the pond and existing dyke. To ascertain the type of soil and its

properties at various locations. To ascertain the depth of water table.

A total of 22 bore holes were drilled, some at the

crest of the existing dyke, some at the toe and others

in the ash pond. Standard penetration test (SPT) waconducted as per IS 2131(1981) and undisturbesamples were taken for the evaluation of engineerinproperties of soil.

RESULTS OF LABORATORY TESTS ON ASH

The results of laboratory tests of 5 samples receivefrom site and mixed samples are summarized in Table

TABLE 1: Geotechnical Properties of Coal Ash

On the basis of the laboratory tests, the followinobservations are made:(a) The ash is predominantly sandy silt though i

one sample the sand content is observed to blarger.

(b) The ash is non-plastic in nature.(c) The OMC is observed to vary from 28 to 37

and the maximum dry density is observed to varfrom 1.06 to 1.21 gm/cc in standard Proctor tes

(d) The shear strength of compacted ash can b

characterized by C= 0 and = 31 degrees.

INFERENCES FROM SITE INVESTIGATIOREPORTSite investigations report indicated the following:(a) The crest width of the existing dyke is 3.0m an

the height varies between 3.7m to 8.45m adifferent locations.

(b) The downstream slope of the existing dyke haan inclination of 2.5: 1.0 (h:v).

(c) The depth of water table varies between 2.45 t6.40m below the ground surface.

(d) The depth of ash is observed to vary from 4.5 t10.6 m below the crest of the embankment andto 3.0 m below the toe of the embankment.

(e) The sub soil comprises of silty sand.The following properties of the ash and soil havbeen used for design on the basis of the sitinvestigation report:(a) Ash: Unit weight = 12 kN/cu.m

C= 0, = 31 deg

(For colour figure, refer to CD)


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Singh and Datta 50

(b) Soil: Unit weight = 20 kN/cu.mC = 0, = 32 deg

STABILITY ANALYSISStability analysis was performed using standardsoftware GEOSLOPE version Slope/W 2007. The

existing dyke adopted for stability analysis comprisedof ash as the embankment material and silty sand asthe subsoil. Raising of dyke was considered by theupstream method of construction. Factor of safetyof 1.5 and above is considered to be acceptable forlong term stability. The analysis was done for thefollowing cases:Stability of Existing (Starter) Dyke (without seepage)Stability of existing (starter) dyke was analysedwithout seepage (dry case). The minimum factory ofsafety is observed to be close to 1.5 which showsthat the embankment is stable.Stability of Existing (Starter) Dyke (with seepage)If slurry water remains ponded behind the exisiting(starter) dyke for excess period of time, seepage canoccur through the dyke. The factor of safety isobserved to fall below 1.0, making the dyke unstable.As reported by field engineers, such a case is notobserved at GNDTP Bhatinda ash pond where water

percolates downward or dries up by evaporation.However, internal drains (rock toe, toe drain and sidedrain) are provided in starter as well as raised dykesas remedial measures to drain off ponded water.Stability Analysis with 3 m RaisingStability analysis of existing dyke with 3 m raisingwas carried out. The minimum factory of safety isobserved to be 1.66 which is above 1.5 and hence,the embankment is stable.Stability Analysis with 6 m Raising

The minimum factory of safety for 6 m raising isobserved to be 1.53 which shows that theembankment is stable.

DESIGN: RAISING OF DYKE BY 3.0MFigures 1, 3 and 4 shows the components of the ashdyke designed for raising the height by 3.0m by theupstream method. The following are the key features:

(a) Crest width : 3.0m(b) Height : 3.5m

(c) Outer slopes (both upstream andownstream): 2.5 : 1.0

(d) Main material (hearting): compacted ash(e) Cover: 0.5m thick made of local soil which wi

support vegetation(f) Internal drains (chimney and blanket

consisting of sand having less than 5% fineas shown in Fig. 1.

(g) Rock toe for raised dyke: As per details showin Fig. 3.

(h) Toe drain, cross pipe drain for raised dyke: ashown in Fig. 1.

(i) Contrary slopes (1 in 500) are provided at 5m interval for longitudinal alignment of todrain.

(j) Rock toe and toe drain along starter dykThese are remedial measures for starter dykas shown in Fig. 4.

(k) Erosion protection: Vegetative cover (locgrass which is self sustaining) is to bprovided on the upstream and downstreamslopes; suitable lining / riprap may bconsidered if erosion due to wave action observed on upstream slope.

(l) Free board : 0.6m

DESIGN: RAISING OF DYKE BY 6.0MFigures 2 through 4 show the components of the asdyke designed for raising the height by 6.0m by thupstream method. The following are the key feature

(a) Crest width : 3.0m(b) Height : 6.5m(c) Outer slopes (both upst ream an

downstream): 2.5 : 1.0(d) Main material (hearting): compacted ash

(e) Cover: Same as 3 m raising(f) Internal drains (chimney and blanket): Sam

as 3 m raising(g) Rock toe for raised dyke: Same as 3

raising(h) Toe drain and cross pipe drain for raise

dyke: Same as 3 m raising(i) Rock toe and toe drain along starter dyk

Same as 3 m raising(j) Erosion protection: Same as 3 m raising

(k) Freeboard : 1.0 m


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DESIGN: CENTRAL DYKE FOR PIPELINESFigure 5 shows the components of the ash dykedesigned for placement of pipes as a central(partition) dyke. The following are the key features:

(a) Crest width : 3.0m(b) Height: up to 3.0m

(c) Outer slopes (both upstream anddownstream): 2:5:1:0

(d) Main material (hearting): compacted ash(e) Cover: Same as 3 m raising(f) Internal drains (chimney and blanket):

consisting of sand having less than 5% finesas shown in Fig. 5.

(g) Rock toe: Same as 3 m raising(h) Erosion protection: Same as 3 m raising

INFLOW POINTS FOR SLURRY WATERThe inflow points where slurry water is dischargedfrom pipelines should not damage the raised dykes.The discharge should be at least 50m away from thetoe / heel of the raised dyke by a suitable arrangementwhich moves the mouth of the discharge pipe insidethe ash pond. Alternatively the slope and base of theraised dyke or central partition dyke, at inflow points,should be protected as shown in Fig. 6.

CONSTRUCTION ASPECTS(a) Construction of dykes for raising the height willbe done on dry ash pond area. If an area has beenponded in the recent past, it must be allowed to dryout for at least 30 days.(b) The top 0.3 m of the ash at the surface of the ashpond will be excavated and re-compacted in the samemanner as for the dyke.(c) Ash for the dyke will be compacted at OMC in

layers of 350mm thickness using vibratory smoothsteel-drum rollers.(d) The roller speed and number of passes will bedetermined from field trial embankment and minimum95% of Proctor Maximum Dry Density will beachieved.(e) A standard quality control programme will befollowed as for monitoring the quality of compactionof ash as for earthworks.

(f) To prevent dust emissions, the ash will be coverewith local soils as early a possible.(g) Material for construction of drains and filtermust meet the filter criteria.(h) Opinion of a local horticulture expert may be taketo ascertain the type of vegetative cover to b

provided, keeping in view the local soil and climaticonditions.

CONCLUDING REMARKSIn the existing dyke, no slurry decantatioarrangement was provided and F.O.S of the startedyke falls below 1 in case of seepage occurs througdyke. Therefore, necessary arrangement for safe exof slurry water has been provisioned from stabilitpoint of view.Results of stability analysis in section 6.2 indicatthat seepage of water through the existing dyke undecondition of prolonged ponding can affect thstability of the dyke. At present such a condition hanot been observed. However, as the height of dykis raised, the head of water increases and thpossibility of seepage increase. Hence monitoring ophreatic line inside the existing starter dyke recommended by use of piezometers. Open stan

pipe piezometers, up to a depth of 10m from the creof the existing embankment may be installed at spacing of 250m along the dyke. If seepage detected by the development of phreatic line, remedimeasures in the form of a suitable berm and ainternal drain on the downstream side of the existindyke would have to be adopted.

REFERENCESGandhi, S.R; Raju, V.S. and Kumar, V.(2000) (Ed

Management of Ash Ponds, Narosa PublishinHouse, New Delhi

Gulhati S.K. and Datta M. (2005) GeotechnicaEngineering, Tata McGraw-Hill Pub, New Delhi

IS 2131 (1981) Method for Standard Penetration Tefor Soils,Bureau of Indian Standards, New Delh


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Singh and Datta 50

Fig.1 Raising of Dyke by 3M

Fig 2 Raising of Dyke by 6M

Fig 3 Details of rock toe of raised dyke


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Fig 4 Details of toe drain and rock toe for starter dyke

Fig.5 Cross section of Central Dyke

Fig 6 Protection Details of Central Dyke at Inflow Points


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INTRODUCTIONTailings dams that were built by hydraulic filltechniques show high variability in their geotechnical

characteristics. The evaluation of thesecharacteristics, which changes by depositionalvariables and tailings characteristics, is extremelyimportant to understand the behaviour of tailingsretaining structures and guarantee their stability.

The technical literature refers to the large number ofreconstituted tailings samples, which are made byspecial remoulding techniques, for the determinationof resistance and hydraulic parameters of these

structures. However, it is also known that thehydraulic deposition process can generate depositswith several layers and bedding forms due tovariability of the size and density of particles andflow process. These structural features, which aretypical of hydraulically deposited landfills, aredifficult to recreate in laboratory when using granularsamples produced by remoulding techniques asreferred above.

To deal with uncertainties that are inherent toreconstituted samples, a methodology to obtain

The Effects of Iron-waste Samples in the Characterization of TailingsDam Behaviour

J G MilonasManagement of Geotechnical and Hydrogeology, Vale S.A ([email protected])

L F M RibeiroDepartment of Civil Engineering, University of Braslia ([email protected])

A P AssisDepartment of Civil Engineering, University of Braslia ([email protected])

ABSTRACT: The geotechnical behaviour of hydraulic fills is strongly dependent on the depositioncharacteristics, which tend to control the strength, permeability and deformability properties of tailings dams.However, this analysis is complex due to the difficulty of obtaining representative samples of field conditions.An alternative to solve this problem has been the use of reconstituted samples that simulate the field patterns.Hence, these methodologies not always simulate all relevant depositional effects. Aiming to support thesample reconstitution process of iron waste tailings, this work presents an alternative methodology of obtainingundisturbed samples from the deposits formed by the hydraulic deposition simulation equipment. It can beconcluded that the methodology to collect undisturbed samples linked to hydraulic deposition simulation testsproved to be an advance in the evaluation of tailings dam behaviour.

undisturbed granular iron ore samples is developedThese samples came from deposits that were createby hydraulic deposition simulation tests i

laboratory.

To evaluate of the hydraulic deposition procesinfluence in the geomechanical behaviour of tailingdams, a comparative analysis of resistancparameters was performed. These parameters werdetermined by drained triaxial tests and referespectively to undisturbed samples anreconstituted samples. Both of them present similacharacteristics such as density, humidity, specifi

mass of grains, and grain size distribution.

HYDRAULIC FILLSDams that are built by hydromechanical techniqueare landfills whose process is associated to thhandling, transportation, and distribution of thconstruction material by humid means. In thhydraulic deposition process, grains tend to deposor flow near the landfill surface according to differenflow regimes. The interaction between the flowinsediments and the deposited layer generate


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changes in the formed layer. These changes arecaused by the accumulation and/or erosion ofsediments and generate distinct sedimentarystructures that, as a consequence, produce distinctgeotechnical characteristics.

The segregation of particles along the flow path isthe main feature of hydraulic fills. The segregationgenerates a significant effect on the density,geometry of the deposition path, and grain sizedistribution of the deposit. The characteristics ofhydraulic fills depend on the tailings composition(grain densities, fluid viscosity, etc.) and thedeposition method. In this context, the hydraulicdeposition process creates typical structuralcharacteristics such as beddings, depositional

microstructures, etc. which are difficult to be createdin laboratory by remoulding samples.

EQUIPAMENT AND MATERIALS

The Hydraulic Deposition Simulation Test (HDST)The Hydraulic Deposition Simulation Test (HDST)was developed by Ribeiro (2000). That equipmentaims the study of hydraulic deposition mechanismsthrough physical simulations in laboratory. These

simulations seek to evaluate the geotechnicalbehaviour of tailings deposits with regard to somevariables (flow characteristics, discharge rate, mudconcentration, etc.) that affect hydraulic deposition.The test allows the collection of representativesamples in order to obtain geotechnical parametersthat are similar to the field parameters.

The HDST apparatus consists basically of three parts:the feeding system; the deposition channel, the main

HDST part; and the discharge system. These elementsare necessary to simulate the landfill characteristics.Moreover, they work in an integrated manner in orderto keep stable the flow parameters and othernecessary conditions for a controlled hydraulicdeposition process.

The deposition channel is 6.0 meters long, 0.4 meterswide and 1.0 meter high. Its glass walls allow thevisualization of the whole deposition process along

the channel. The feeding system is constituted by

two reservoirs and a special pump that promotes thcontinuous movement of the mixture (tailings anwater) in order to maintain the concentration constanduring the test.

The mud discharge in the channel is performed b

means of a flow controller that keeps the mud parallto the channel walls in order to produce a uniformflow and minimize possible effects of them. At thfinal portion of the channel there is a drainage systemto keep the level of the decantation pond constanby eliminating the excess of water. Figure 1 showsschematic drawing of the equipment. More details othis equipment and test procedures can be found iRibeiro (2000).

Fig.1 Schematic drawing of the Hydraulic DepositioSimulation Test (HDST) (Ribeiro, 2000).

Iron waste of the gua Limpa ComplexTailings used in these studies come from the iron orprocessing of the mine of the gua Limpa Complein Brazil. This mine, which belongs to Vale, is locatein Rio Piracicaba (MG) at a distance of 140 km from

Belo Horizonte, the state capital. These tailings hava typical grain size distribution that corresponds tmedium to fine sands. Table 1 displays values otypical parameters of the iron tailings of the guLimpa Complex Mine.

TABLE 1 Characteristics of the Iron Tailings from guLimpa Mine (Espsito, 2000 and Ribeiro, 2000)

D10 a (mm) D50

b (mm) D90 c (mm) Cud Gs

e

Fef(%) SiO2g(%) Al2O3

h (%)

0.06 0.19 0.48 4 3.1 23 67 0.40


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Milonas, Ribeiro and Assis 51

aEffective diameter; bAverage diameter; cDiameter thatcorresponds to 90% in the grain size distribution curve;dUniformity coefficient; eRelative density of the solidparticles; fIron; gSilicon oxide; hAluminum oxide.

METHODOLOGY FOR OBTAININGUNDISTURBED SAMPLESTo obtain undisturbed samples, the hydraulicdeposition simulation test was performed using thesame procedures presented by Ribeiro (2000).Approximated values of 15% by weight of the mixtureconcentration and 15 l/min of flow rate were adoptedduring the simulation test. These numbers representthe common values used in previous simulation testsusing iron tailings in the HDST.

To obtain undisturbed samples, successive hydraulicdeposition simulations were performed to build adeposit with a thickness higher than 10 cm (height ofthe undisturbed sample) in the central region of thedeposition channel or at 3.0 meter distance from thedischarge point. The drainage system of thedeposition path was carefully controlled in order topromote a subaquatic deposition at the final portionof the deposition channel.

After concluding the hydraulic deposition, the

material deposited in the channel was kept still for 24hours approximately to drain the excess of water alongthe deposition path and guarantee good samplingconditions.

Samples were collected in four points along the HDSTchannel. The first point was situated close to the

discharge point of the channel. For each point, threundisturbed samples were collected for triaxial angeotechnical characterization tests. These locationalso provided material for reconstituted samples thwere submitted to the same tests. Figure 2 illustratethe scheme of the sampler points in the HDS

deposition channel. Their position was chosen witthe purpose of evaluating and analyzing possiblstructural variations of the deposit by hydraulisegregation.

Two-part cylinders were especially designed tcollect of undisturbed samples. They have thin waland a wedge-shaped extremity to facilitate thepenetration into the layer. Their dimensions arinternal diameter of 47 mm, height of 100 mm, an

thickness of 1.2 mm.The methodology to collect undisturbed samples cabe briefly described by the following stagespreparation and levelling the surface of the deposregion to be sampled; positioning of the cylinderand lateral paring of the core; careful penetration othe cylinder; removal of samples from the HDSchannel; packing, identification, and conditioning osamples in the controlled temperature-moistur

chamber (Milonas, 2006).The lateral paring combined with the use of thinwalled cylinders tends to minimize the impact causeby the penetration process. All the procedures wercarefully realized in order to minimizing thdisturbance. Figure 3 illustrate the process oobtaining undisturbed samples.

Fig.3 Lateral paring of the core and sample removfrom the HDST channel.

Fig.2 Scheme of the distribution of samples along theHDST channel: (a) longitudinal section; (b) top view.(For colour figure, refer to CD)


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Concerning the characteristics of the undisturbedsamples, Fig. 4 shows typical depositional structuressuch as beddings and others features that were keptin the samples from the HDST.

(a) (b)

Fig.4 Undisturbed samples from different locations

used in the triaxial tests: (a) at the 2.8-meter distancefrom the discharge point; (b) at the 0.1-meter distancefrom the discharge point.

SAMPLE REMOULDING PROCESSIn general, the remoulding process occurredhomogeneously by the simple deposition of materialin layers followed by the dynamic compaction. Thisaims to give the material the same density of theundisturbed samples or in the field. Inaddition todensity, other conditions such as water and ironcontent, grain size distribution were recreated. Thismethodology was standardized with the purpose ofcreating conditions to compare the results obtainedfrom undisturbed samples and their reconstitutedcounterparts.

However, in the remoulding process, typical depositionalstructures are not reproduced and, as a consequence,samples display homogeneous profiles (Fig.5).

Fig.5 Reconstituted sample (0.1A) submitted to triaxial

test

LABORATORY TESTS

Geotechnical CharacterizationThe characterization tests of tailings referred in thpaper followed integrally the guidelines of thBrazilian Standard Test Method (ABNT).

The density of iron particles is greater than thdensity of silica grains. This property exerts stroninfluence on the specific weight of tailingTherefore, small variation of the iron content cacause significant change of their specific weight. Fotailings from the gua Limpa Complex mine, Espsit(2000) observed a linear relation between specifiweight of grains and iron content and proposed thEquation 1 to relate these variables.

sa= 0.025 FEb+ 2.60 (1)aSpecific weight of grains (g/cm3); bIron content.

Table 2 displays the results of the geotechnicacharacterization of undisturbed samples, and Fig.shows the corresponding grain size distributionEquation 1 was used to determine the iron contenof the HDST-collected samples.

TABLE 2 Geotechnical characteristics of undisturbesamples.

Spl wa b dc

sd Fee nf eg

(%) (kN/m3) (kN/m3) (kN/m3) (%)

0.1A 12.1 23.1 20.7 35.9 42.4 0.42 0.70.1B 12.4 24.6 22.0 38.0 51.2 0.42 0.70.1C 12.7 22.6 20.0 35.9 42.4 0.44 0.71.0A 14.9 22.5 19.5 33.9 34.4 0.42 0.741.0B 12.2 24.5 21.9 36.8 46.0 0.41 0.61.0C 12.7 20.9 18.5 31.5 24.4 0.41 0.7

2.0A 15.2 20.5 17.8 30.5 20.4 0.41 0.72.0B 14.6 20.6 17.9 29.0 14.4 0.38 0.62.0C 15.4 18.8 16.3 28.4 12.0 0.43 0.72.8A 12.6 20.2 17.9 27.7 8.8 0.39 0.542.8B 10.7 18.5 16.8 27.9 10.0 0.40 0.672.8C 14.3 20.0 17.6 28.2 11.2 0.38 0.6

aWater content; bNatural specific weight(kN/m3); cApparedry specific weight(kN/m3); dSpecific weight of the solid(kNm3); eIron percentage; fPorosity, and gVoid index.




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The geotechnical properties related to undisturbedand reconstituted samples presented similar values.In the remoulding process the main physicscharacteristics were carefully reproduced in order toallow the comparisons. Considering this aspect, theremoulding process of samples for triaxial tests could

be considered satisfactory. The data obtained fromthe remoulding samples were analogous to theundisturbed ones presented in Table 2. Thehomogeneity was the only different feature.

0

20

40

60

80

100

0.0001 0.001 0.01 0.1 1 10

Particle Diameter (mm)

%

Passing

Sample 1 - 0.1 m

Sample 2 - 1.0 m

Sample 1 - 2.0 m

Sample 1 - 2.8 m

CLAY SILT SAND GRAVEL

Fig. 6 Grain Size Distribution.

Triaxial Tests

For the determination of strength parameters of iron

ore tailings, drained triaxial tests were performed

applying confining pressures of 50, 100, and 200 kPa.

Two samples were used: undisturbed samples, which

are representative of the hydraulic deposition process,

and homogeneous reconstituted samples. The

specimens were saturated, compressed and sheared

according to procedures suggested by HEAD (1986).Saturation was monitored, ensuring B values of at

least 0.98 for all specimens. The triaxial tests were run

at a sufficiently low axial displacement rate to ensure

full drainage within the sample (0.07 mm/min).

The shear strength behaviour from triaxial tests with

an undisturbed sample and a remoulding sample

related to 1.0-meter from the discharge point are

shown in Figure 7 and 8 respectively.

0

200

400

600

800

1000

0% 5% 10% 15% 20%

Axial Strain (%)

1

-3

(kPa)

50 kPa

100 kPa

200 kPa

(a )

(b)

Fig. 7 Response of the undisturbed sample collected the 1.0-meter distance from the discharge point: (a) stress

strain curves, (b) Shear strength envelope

0

200

400

600

800

1000

0% 5% 10% 15% 20%

Axial Strain (%)

1

-3

(kP

a)

50 kPa

100 kPa

200 kPa

(a )

(b)

Fig. 8 Response of theremoulding sample at the 1.0meter distance from the discharge point: (a) stress-strai

curves, (b) Shear strength envelope.




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Considering the strength parameters, Table 3

summarizes the results of all triaxial tests carried out

in both kinds of samples.

TABLE 3 Strengthparameters from triaxial tests.

Samples Undisturbed Remoulding

Samples naverage

a ()b ()b

0,1 0,43 38,5 34,9

1,0 0,41 38,7 35,2

2,0 0,41 38,7 35,6

2,8 0,38 41,3 36,2

a Porosity, b Effective frictional angle

Although the undisturbed samples and theirreconstituted counterparts show similar density,

water content, grain size distribution, porosity and

iron content, the stress-strain curves suggest a

distinct behaviour and show the influence of the

deposition process. Additionally, it can observe an

increase in the strength parameters linked to the

undisturbed samples

ANALYSIS OF RESULTSThe laboratory-testing program here described

allowed the analyses of the variability of geotechnical

parameters as a function of the hydraulic deposition

process. This process is associated to erosion and

deposition events, related to the segregation pattern.

The particles movement, characterized by rolling and

sliding, is evidenced by the formation of beddings in

the flow direction represented by a sequence of iron

and quartz bands.

Near to the discharge point, the deposit contains

higher concentration of fines and iron particles.

There is an increase of the average diameter of

particles in the central part of the deposit, associated

predominantly to quartz particles. This fact can be

explained by the high values of specific gravity linked

to the iron particles and consequently highest

velocities to transport them. These observations

reinforce the results obtained by Ribeiro (2000

Hernandez (2002), and Presotti (2002) using simila

iron wastes. These authors demonstrated that th

segregation of iron ore tailings occurs predominantl

due to the weight of particles.

In the present studies, the porosity decreaseslightly, indicating the existence of denser and mor

stable deposits at the 3.0-meter distance from th

discharge point.

In addition to the hydraulic deposition process, hig

variability of geotechnical parameters was als

observed along the transversal section of the channe

These differences are probably associated to the flo

pattern, which tends to generate small channels b

formation of small barriers that redirects the flow an

produces some regions with different physic

characteristics.

HDST-originated undisturbed samples were able t

keep beddings and other structural features that wer

generated during the hydraulic deposition as show

before. The sample remoulding process wa

considered satisfactory because it was able t

reproduce some of the properties of the material from

the HDST deposition channel, however i

homogeneous conditions.

Strength parameters are higher for undisturbe

samples than their reconstituted counterparts. Stres

strain curves revealed different behaviours for bot

samples. Undisturbed samples display a fragil

behaviour while their reconstituted samples have

ductile behaviour. In general, undisturbed sample

present a well-defined failure surface. On the othe

hand, the reconstituted samples produced a bulge i

the central region instead of defining any failursurface (Fig.9). The effective frictional angles () oundisturbed samples were 3o to 4ohigher than th

reconstituted samples (Table 3).

The different behaviour of undisturbed samples ca

be associated to a larger interlocking of grain

generated during the hydraulic deposition. Tha

interlocking keeps the particles packed to each othe


14/118

and creates, as a consequence, a larger link among

them. The existence of beddings parallel to the flow

direction also helps explain the distinct behaviour of

undisturbed samples. It is important to reinforce that

these features were not reproduced during the

remoulding methodology.

(a) (b)

Fig.9 Final aspect of specimens obtained at 2.8-meterfrom the discharge point for the confining pressure of 100

kPa. (a) undisturbed sample, (b) reconstituted sample.

Figure 10 represents the response of frictional angle

versus average porosity. It can observe that an

increase in the porosity represents a decrease in the

value obtained for both sort of samples. It is alsoobserved that undisturbed samples show better

results than their reconstituted counterparts. This

difference, which is close to 10% in numerical terms,

emphasizes the importance of the deposition effects

for the geomechanical behaviour of iron ore tailings.

Fig. 10 Relationship between frictional angle andporosity.

CLOSING REMARKSThe applied methodology to collect undisturbe

samples, which is associated to hydraulic depositio

simulation tests, showed to be an important advanc

in the evaluation of the geotechnical behaviour o

tailings dams. Some results have already indicate

this as a matter of fact. However, it is important temphasize that this methodology is still at th

beginning and additional studies are necessary t

improve it. This work seeks to develop idea

concerning the behaviour of hydraulic fills throug

the use of undisturbed samples by HDST simulation

This approach became feasible due to the advantage

that the HDST apparatus offer in order to reproduc

field conditions. In relation to the researches alread

realized with the HDST, most of them hav

demonstrated the applicability of the equipment t

forecast the geometry, grain size distribution, an

density of tailings dams construction by hydrauli

fill method (Ribeiro, 2000; Cavalcante, 2000). Th

collection ofundisturbed samples along the HDS

deposit presents an innovative character an

demonstrates the importance of the application o

physical simulations to estimate the hydraulic fil

behaviour.

REFERENCES

Cavalcante, A.L.B. (2000) Efeito do Gradiente d

Permeabilidade na Estabilidade de Barragens d

Rejeito Alteadas pelo Mtodo de Montante,MSDissertat ion, , Department of Civil an

Environmental Engineering, Univers ity o

Braslia, 186 p.

Espsito, T.J. (2000) Metodologia Probabilstica Observacional Aplicada a Barragens de Rejeit

Construdas por Aterro Hidrulico, PhD ThesiDepartment of Civil and Environmenta

Engineering, University of Braslia, 363 p.

Head, K.H. (1986) Manual of Soil Laboratory Testin

London, UK: Pentech Press, Vol.3, 1240 p.




15/118


Hernandez, H.M. (2002) Caracterizao Geomecnicade Rejeitos Aplicada a Barragens de Aterro

Hidrulico,MSc. Dissertation, Department of Civiland Environmental Engineering, University of

Braslia, 174 p.

Lopes, M.C.O. (2000) Disposio Hidrulica deRejeitos Arenosos e Influncia nos Parmetros deResistncia, MSc. Dissertation, Department ofCivil and Environmental Engineering,

University of Braslia, 157 p.

Milonas, J.G. (2006) Anlise do Processo deReconstituio de Amostras para Caracterizaodo Comportamento de Barragens de Rejeitos de

Minrio de Ferro em Aterro Hidrulico, MSc.

Dissertat ion , Department of Civil an

Environmental Engineering, Univers ity o

Braslia, 146 p.

Presotti, E.S. (2002) Influncia do Teor de Ferro noParmetros de Resistncia de um Rejeito d

Minrio de Ferro,MSc. Dissertation, Departmeof Civil Engineering, Federal University of Our

Preto, 153 p.

Ribeiro, L.F.M. (2000) Simulao Fsica do Processde Formao dos Aterros Hidrulicos AplicadoBarragens de Rejeitos, PhD. Thesis, Departmen

of Civil and Environmental Engineering

University of Braslia, 235 p.


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Optimization of the Inwash Technology of the CascadeTailing Dump Levee in Permafrost Region

A.B. Lolaev,

North Caucasian Institute of Mining and Metallurgy (State Technological University), Vladikavkaz,

Russia ([email protected])V.V. Butygin

Norilsk Institute of Industry, Norilsk, Russia ([email protected])

A.P. Akopov,


Russia ([email protected])

A.Kh. Oganesian,



M.N. Sumin



ABSTRACT: The exploitation of the tailing dump in Norilsk industrial region (north of Siberia)has begun since 1983 with the purpose of warehousing of tails and organization of system of

turnaround water supply. The tailing dump is the cascade type of dumps with difference in

grades of the tops of dams about 20 meters. The technology of controlled inwashing of the

levee was designed and recommendations for stability providing were carried out. The results

of investigations will permit to provide safety exploitation of tailing dam, improve the

environmental situation in the region and increase the efficiency of production.

INTRODUCTION

High level of industrialization of northern regions of

Russia causes significant geocryological problems

in the soil. Only in Siberia in the areas of large mining

and metallurgical enterprises dozens of million cubic

meters of different deposits have been accumulatingfor a long time in the tailing dumps.

Sufficient attention has been given lately to this

problem of geotechnics of mining, metallurgical

wastes and tailing dams in Norilsk regions (Lolaev

et al., 1997, Lolaev et al., 2004, Lolaev and Butygin,

2005).

The problem of capacity increasing of operating

tailing dumps becomes more and more urgent with

the further economic development. Taking int

account the fact, that disposal area should functio

for 15- 20 years, the main objective of this paper

to develop the special technology of inwash of th

cascade type of the tailing dump in Norilsk regio

for its operation period and make in-sit

investigations of these techniques.

CASE HISTORY

The climatic characteristics of Norilsk industri

region are:

average annual temperature of the air is -9.4 0C

the maximum temperature of the air is +32 0C an

the minimum temperature is -56 0C;

the maximum speed of wind is 40 m/sec;

winds with speed above 15 m/sec are observeduring 90 days;


17/118


the strong winds and snowfalls are observed up

to 130 days a year;

average amount of precipitations is 564.5 mm per

year.

The object of research of the present work is the

tailing dump Lebyazhie, located on the territoryof Norilsk industrial region.

The exploitation of the disposal area has begun

since 1983 with the purpose of warehousing of tails

from concentrating mill and organization of system

of turnaround water supply (Recommendations,

1977).

The basic hydraulic engineering structures include:

pool for reception of pulp and storage of tails

local tailing dam;

system of pipelines for transportation of pulp

system of pipelines for turnaround water supply

with coastal and floating pump stations

spillway system

The disposal area provides sedimentation,

clarification and natural stabilization of ionic

structure of turnaround water acting with tails. Theclearing of water from firm phase is done with the

help of gravitation method.

The constructive characteristics of the dam are:

1. the disposal area - 4.02 sq.kms

2. the length of the tailing dam - 8.1 kms

3. the tailing dam is carried out as a persistent

drainage prism from metallurgical slag:

the width of the prism - 8 m the length of the prism - 8500 m

4. the capacity of disposal area - 16.7 mln. m3

5. the settlement term of operation - 20 years

6. the height of the dam - 39.3 m;

7. the inclination of a top drain level - 1: 50

8. the inclination of a bottom slope - 1: 4

9. the maximal depth of pool 4.7 m10. the average depth of pool 2.5 m.

The exploitation period of the tailing dump was

planned for twenty years.

TEST RESULTS AND DISCUSSION

Since 1992 in connection with the changes i

technological processes of concentrating mil

reduction of volumes of processing of ores an

complexities in transportation of tails, the norther

part of a tailing dam practically was not raised, thhas resulted in considerable reduction of capacit

of pool. The decision about tailing dam filling b

old (stale) tails was accepted in 1997 for the rapi

rise.

The data obtained during the field and laborator

researches have made the reasons and productio

of physical model of the inwashing of the tailin

dump. With the help of this model the know

technologies of constructions of such type of tailin

dump, were estimated, the exploitation data wa

analyzed, the suggestions of exploitation service

were approved.

As a result of mutual research-and-productio

investigations the technology of controlle

inwashing of the levee was designed. It include

the following operations:

the construction of the retaining prism from

metallurgical slag. The metal distributin

slurry pipeline is laid on it;

the construction of ring slag fill in the beac

zone at the specific distance from the ax

of the distributing slurry pipeline. It retain

the solid particles in the beach zone an

simultaneously it illuminates the wate

coming into the pool.

The scheme of the levee inwash is shown in Fig.

Functions of a slurry collecting prism in operatio

of an inwash are the following:

Fig. 1The Scheme of the Levee Inwash


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1 - distributive slurry pipeline; 2 - geotextile anti-

filtration screen; 3 load; 4 a slag prism; 5 aretaining prism of a dam; 6 slurry collecting slagprism

slurry collecting prism promotes more intensiveconsolidation of hydraulic fill tails and increase

of stability of a dam; it allows operating of bottom contour formation

in pond zone that is rather an important factor

that provides winter storing of tails under ice;

it promotes more intensive frost penetration inan inwash massif that raises its static and

filtration stability and in that way provides

environmental safety of the tailing dump;

it carries out reinforcing a body of a leveefunction.

On a backslope of a dam an impervious screen from

geotextiles is being placed. The inwash is made by

sections of 800-1000m in width, after formation of a

layer of tails with the capacity of H0,5 m, hydraulicfill section is left for rest(10-15 days). The givenway of an inwash already for the first years (1997-

1998) has provided an advance growth of a dam.

This measure has allowed to increase the height of a

dam and the capacity of the disposal area for the next

10 years. Today the top of the dam is about 70 m.

Now, in connection with planned substantial growth

of an exits of tails there was a new problem emerged

the increase in the capacity of the Lebyazhietailing dump and its service time. Therefore

optimization of the inwash technology of the tailing

dump was carried out in view of this important

condition.

From 2006 the tailing dump has the second tailing

pond. The second pond is under the construction.

The top of the dam of the second pond is about 50

meters now. Thus the tailing dump Lebyazhieisthe cascade type of dumps with difference in grades

of the tops of dams about 20 meters. Planned level

of the top of the dam is 90 meters.

The constructive characteristics of the second

tailing pond and dam are:

1. the disposal area - 2.4 sq.kms

2. the length of the tailing dam - 4.3 kms

3. the tailing dam is carried out as a persistent

drainage prism from metallurgical slag:

the width of a prism - 8 m

the length of a prism - 4313 m

4. the capacity of disposal area - 16.7 mln. m3

5. the settlement term of operation - 20 years

6. the height of dam 19-20 m;7. the inclination of a top drain level - 1:50-1:100

8. the inclination of a bottom slope - 1:4-1:5

9. the maximal depth of pool 5.2 m10. the average depth of pool 2.9 m.

Despite the received beneficial effects o

introduction of technology of an operated inwas

of a levee on the second tailing pond, its practicrealisation is connected with the considerabl

material and financial expenses, connected, in the

turn, with the annual relifting of a dam, resurfacin

of slurry pipelines, etc.

Optimisation of the inwash technology has bee

executed by the following criteria: stability of th

levee; decrease in material and financial expense

for operation; industrial and environmental safet

of a construction, the maximum use of capacity etThe technology which satisfies all criteria

considered to be the optimum one.

As the basic technological variants of operation th

following ones were being considered:

1. Operation of two fields by turns, achievemen

of a design elevation by the first field, with la

of growth of a dam ridge of the second field an

operation of two ponds.

2. Operation of two fields by turns with aadvanced inwash of a levee of the second fiel

and operation of two ponds.

3. An advanced inwash of the second field befor

achievement of a ridge of a levee of the fir

field and the further operation of integrate

tailing dump with one pond .

Variants of inwash and warehousing of tails wer

investigated by means of physical and mathematic

modelling. Object of researches was th

Lolaev et al. 51


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substantiation of parametres of modelling,

conformity from positions of the theory of model

tests similarity of results to the results of tests in-

situ, modelling of inwash methods of two fields

during the summer and winter periods. On the basis

of the analysis of mathematical calculations and

results of model tests the optimum technologicalparametres of the inwash scheme of the dam were

defined in the course of approbation.

The developed technology of the dam inwash takes

into consideration the height of a dam inwashed for

one cycle and as a whole for a year, the width of

front of an inwash, the quantity of the inwashed

tails, operations schedule etc. The beach sectoring

for the determination of the volume of the inwashed

tails is presented in Fig. 2.

Fig. 2 The Beach Sectoring

The quantity of the inwashed tails for a cycle was

defined further. The inwash of the dam is made by

gradual moving of the inwash sections 900-1200 m

in length (Fig. 3).

Fig. 3 Sequence of the Sections Inwash

The schedule of the inwash works is made for the

whole year. This, in its turn, has allowed to design

the duration of the dam operation until achievementof its design elevation (Fig. 4).

Fig. 4 Scheme of a Dam Inwash on Years

During the inwash process and the subsequen

consolidation the values of physical and mechanicproperties of the filled-up grounds are bein

established. The changes of the dam stabilit

coefficient during the working life are carried out.

The obtained results are included in a database an

can be replenished in the course of reception of ne

data about the structure of the inwashed body o

about the physical and mechanical properties of tai

composing it. On the basis of the carried out work

the generalisation of the results is being made antechnological regulations are being developed.

CONCLUSIONS

Thus, the optimisation of the inwash technology ha

allowed: to achieve the increase in the stabilit

coefficient of the dam and of the construction as

whole during its working life, to raise the level of th

industrial and environmental safety, to provide th

achievement to the design elevation of the levels o

the ridges of the first and of the second field damsimultaneously. That will permit to provide th

required capacity for warehousing of the tails for th

whole working life without building of new stores.

REFERENCESLolaev, A.B. et al. (1997). Site investigation of tailin

dam in permafrost region. Proceedings of th

Geoenvironmental Engineering Conference

Lolaev, A.B., Butygin, V.V. and Kaitmazov, N.G. (2004

Environmental Aspects of HydrotechnicaConstruction in Cryolitic Zone.Proc. 7th Inter

Symposium on Cold Region Developmen

Sapporo,Japan

Lolaev, A.B. and Butygin, V.V. (2005). Geologica

and ecological problems of industria

hydraulic engineering in cryolite zon

Moscow: Nedra. 240. (in Russian).

Recomendations on designing the structures of tailin

pools and dams in severe climatic condition

(1977). Moscow: Stroyizdat. (in Russian)


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Acid Mine Drainage Pollution in a Tailings Pond in the State of Mexico

L Lizrraga-Mendiola

University Autonomous of the State of Hidalgo, Mexico ([email protected])

M R Gonzlez-Sandoval, M C Durn-Domnguez

National Autonomous University of Mexico, Mexico ([email protected],

[email protected])

A Blanco-Pin

University Autonomous of the State of Hidalgo, Mexico ([email protected])

ABSTRACTThe mineralogy of tailings deposited in the tailings pond consists of: Pyrite (55%), sphalerite (2%), galena (0.7%), and

chalcopyrite (0.6%). The results from chemical analysis showed that exist pollutants: Fe, Mn, SO42- and Zn. The study

area is divided in two zones: In the zone 1, it was observed the presence of natural weathering, due to a phenomeno

known as acid rock drainage (ARD); on the other hand, in zone 2, there was a clear influence of acid mine drainag

(AMD). Seasonal variations were observed, and the pollutants behavior shows dissolution capacity of rocks antailings during dry and wet season, related to acidic pH values.

INTRODUCTION

Sulphide minerals, such as pyrite, are exposed to

atmospheric conditions and weathered in tailings

impoundments, waste rock piles and walls of pit

lakes. During sulphide oxidation, S and Fe(II) are

dissolved and oxidized, with the assistance of

dissolved O2

and Fe(III). Acid, SO4-rich effluent

that is formed in this process transports heavy

metals and Fe to the environment (Kumpulainen

et al., 2007). Thus, the monitoring and modeling

of the distribution of metals, especially in mining

areas, is an important subject in studies aimed at

the evaluation of environmental pollution (Edet et

al., 2004). Local climate conditions can control

the formation of secondary minerals because the

chemical composition of the draining water can

vary with seasons (Kimball, 1999; Kim et al.,

2002; Yu and Heo, 2001; Schroth and Parnell,2005). Chemical changes in water vary due to

variations in temperature and precipitation. The

objective of this study was to evaluate the

seasonal variation of minerals which control the

acid mine drainage (AMD) and the acid rock

drainage (ARD) generation.

Description of the Study Area

The study area is located SW of the State o

Estado de Mexico, in the central part of th

Mexican Republic (Fig. 1). The altitude is 1200

meters (m.a.s.l.), and the predominant climate i

from temperate to warm (30 C in summer, 10 to

16 C in winter) with dry winter and rainy

summer (1500 mm annual average rainfall).

Processing plant

At the processing plant, the extracted mineral i

crushed and milled to 200-mesh particle size. Th

Zn, Pb and Cu sulfides are concentrated by

flotation, and the remnant materials, around 95%

of the mineral (rich in pyrite -FeS2-), are pumped

as water slurry to the tailings pond. Th

mineralogy of these tailings presents high contentof potentially acidic drainage generating minerals

Pyrite (55%), sphalerite (2%), galena (0.7%), and

chalcopyrite (0.6%). Currently, this mine site i

active; the tailings pond surface area is 132800 m

approximately, and contains around 5.5 million

of tons of tailings (Lizrraga-Mendiola et al

2008).


21/118


Fig.1 Location of the Study Area, as well as the

Sampling Points (Lizrraga-Mendiola et al., 2008).

Methodology

Water and tailing samplings were carried out

during the years 2004-2007. Methodology of

sampling and analysis is discussed by Lizrraga-

Mendiola et al. (2008). For the hydrogeochemical-

modeling, the PHREEQC program was used, andthe Wateq4f database included in this program

was utilized for calculations (Parkhurst and

Appelo, 1999).

Results and Discussion

In previous studies Lizrraga-Mendiola et al.

(2008) have defined the study area into two zones:

zone 1 (upstream the tailings pond, out from the

influence of pollutants), and zone 2 (downstreamthe tailings pond, on the influence of AMD

pollutants migration) (Fig. 1, Tables 1 and 2).

Water chemistry

The results obtained from the chemical analysis

showed that, for both zones (zone 1 and zone 2),

the pH (acid) is below the permissible maximum

limit (PML) (DOF 1994) during wet, but also

during dry seasons; pH (basic) is above the PML

in rainy season and slightly acid during dry seaso

(Table 1).

TABLE 1 Description of Water Samples (Lizrrag

Mendiola et al., 2008)

Sample Description and distance from tailings

pond

PJMA1 Small pond, to the west (250 m)



PJMA4 Rainwater deviated, to the west (150

m)

PJMA5 Water recovered from processing

activities (400 m)

PJMA6 Tailings water deviated through pipes

(350 m)PJMA7 Springwater conducted through pipes

(1500 m)

PJMA8 Groundwater from mines, deposited

as superficial water in pools (1000 m)

PJMA9 El Ahogado river, downstream (1300

m)

PJMA10 El Ahogado river, upstream (950 m)

Only in PJMA9 during dry season (april 2005) pH

value was very acidic. With respect to thparameters that indicate the presence of AMD

almost all of them show to be higher than PML i

every season of sampling (Table 2). Only i

PJMA1 and PJMA2, pH, Mn and Zn were equa

or almost equal to PML. Although it is observed

clear difference between zones 1 and 2, in zone

there is an augment in AMD pollutan

concentration during dry season (acid pH, an

high Fe, Mn, SO42-

, and Zn values).

However, even when there is no direct influenc

in zone 1 from the tailings pond, and when pH

was basic occasionally, there was found th

presence of AMD pollutants also. From thes

results, it can be interpreted that the pollutio

source in zone 1 can be a natural weathering from

rocks, phenomenom better known as acid roc

drainage (ARD).


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TABLE 2 Pollutants found in the Sampling Points around the Tailings Pond (minimum, maximum value)

*PML: Permissible maximum limits (DOF, 1994). Blank spaces mean no contaminant value determined. 2April 2004September 2005, 5January 2006, 6March 2007. Values in bold are almost equal or equal to the PML.

Hydrogeochemistry

From the hydrogeochemical modeling analysis,

the following behavior of these pollutants was

observed: during wet seasons and basic pH values,

pollutants remained on equilibrium or precipitated

(oversaturation); on the other hand, during dry

seasons and acid pH values, pollutants remained

diluted or subsaturated (Table 3). The ionic

strength (I) of water ranges between 7.753-4 and

8.046-2

(mean of 4.06-2

). According to Alpers andBlowes (1994) and Appelo and Postma (1999), the

I for freshwater is normally > 0.02. The values of

the I show that water samples from the area are

fresh. On the other hand, according to Sracek et al.

(2004), in oxidizing environments, like in this

case of study, the principle attenuation mechanism

of contaminants related to AMD is the adsorption

on Fe(III) oxide and hydroxides. Also, the

changes in pH can be related to some redox

reactions, driving dissolution of carbonates an

silicates. Unfortunately, in the study area, there i

no presence of these minerals in abundance to b

considered as an alternative to solve this pollutio

problem. Seiler et al. (2005) found in their stud

that some parameters such as W and Cl in th

Carson River appeared to be controlled b

evaporative concentration, using PHREEQC t

calculate ionic activity product (IAP), an

compared it with Ksp for primary W minerals. Ithis study, PHREEQC is used to observe th

seasonal variation of saturation index values (SI

From Table 3, primary minerals such as FeS

Fe2S, and ZnS are very subsaturated and ar

present in zone 1. From these, pyrite showed to b

the most soluble mineral, liberating Fe during dr

season. Hematite was the only Fe-minera

oversaturated during all sampling seasons (and ha

no presence in zone 2).

Zone 1 Zone 2Mineral species

PJMA14 PJMA22 PJMA24 PJMA25 PJMA74 PJMA44

Ionic strength, I (M) 1.411-3 6.303-4 7.753-4 2.906-4 1.585-3 8.046-2

Anglesite, PbSO4(sec)

Anhidrite, CaSO4(sec) -0.21

Cd(SO4)Celestite, SrSO4 -0.46

Fe(OH)3 (a) 2.94 2.8 -3.39 3.35

FeS (ppt) -83.48

Goethite, FeO(OH) 8.83 8.7 2.51 9.24

Gypsum, CaSO4.2(H2O) 0.02

Hausmannite, Mn3O4(prim)

-9.84 -8.18 -28.82 -14.16 -12.7

Hematite, Fe2O3 19.63 19.81 7.32 20.28

Mackinawite, (Fe,Ni)S0.9 -82.74

Manganite, MnO(OH) -4.32 -4.25 -11.86 -6.11 -5.42

Melanterite,Fe(SO4).7(H2O) (sec)-12.42

Pyrite, FeS2 -137.51

Pirochroite, Mn(OH)2 -5.89 -5.87 -10.91 -7.16 -6.06

Pirolusite, MnO2(sec) -8.75 -7.66 -18.08 -10.72 -11.1

Esphalerite, (Zn,Fe)S -70.96 -47.05

Willemite, Zn2SiO4 0.71 -1.37 -0.62

Zn(OH)2 -1.75 1.24 -2.91 -2.43

Mendiola et al. 52


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TABLE 3 Summary of Hydrogeochemical Results

of Water Samples in zones 1 and 2

2April 2005, 4September 2005, 5January 2006, 6March

2007.

With respect to secondary minerals, Mn-minerals

were the most abundant and are subsaturated

during all seasons of sampling in both zones. In

zone 2, only in PJMA4 there was possible to

analyze the hydrogeochemical behavior due the

scarcity of information. This hydrogeochemical

behavior is congruent with water chemistry

results, indicating that no matters the season of the

year, mineral concentrations are higher enough to

generate AMD or ARD pollution, depending on

the location of sampling points with respect to the

tailings pond. What it was expected is that

sampling points closer to the tailings pond were

more polluted.

Behavior of contaminants

From Figures 2 and 3, there is observed tha

contaminants (Fe, Mn, Zn, and pH and SI) ar

related. When pH was acid, concentration of thes

ions were higher; on the contrary, when pH wa

slightly acid or neutral, ions concentratio

decreased in both zones. This behavior was almosthe same during every season of the year

analyzed for this study. From these, the pH i

zone 2 was the most acidic and the pollutant

concentrations the highest.

Fig.2Contaminants Behavior vs pH.

Fig.3Saturation Index vs pH.

Sample pH Fe Mn SO42- Zn

PML* 6.5-

8.5

0.3 0.05 250 5.0

Zone 1

PJMA1 8.762 0.542,

4.250.054

PJMA2 5.194

,

9.355

0.464,

5.250.054 5.085

PJMA3 5.132 0.262 7.462

PJMA7 4.05

PJMA8 6.24,

3.5465.12,

18.8515.22,

11.542216.45

,

46506

107.

672,

37.56

PJMA10 3.45 39.55

Zone 2

PJMA4 4.55

2

,

4.0854.1

5

,0.486 4.5

2

,8.164 2883.1

2

,

3830417.8

5

,

10.3

16

PJMA5 6.245

,

3.576

48.82,

5.943.182,

12.0162806.52

,

46606

7.422

,

46.25

PJMA6 3.982

,

6.195

5.65,

9.5763.182,

12.8161504.55

,

48806

7.132

,

45.65

PJMA9 2.52 88.562,

0.4647.352,

0.0643786.92

,

2594.0

35

8.152

,

5.05


24/118

In Figure 3, the behavior of SI vs pH shows that, from zone 1, SI was near neutral, and the pH wa

acidic (PJMA2-2), slightly acidic (PJMA1-4 and

PJMA7-3) in all seasons, while pH was basic

(PJMA2-4) during wet season. From zone 2, the

only sampling point represented shows high

dissolution capacity and the most acidic

environment during wet season. From theseresults, it can be mentioned that ARD in zone 1,

and AMD in zone 2 have the potential to produce

pollution through the dissolution of rocks and

tailings minerals, respectively.

Conclusions

This study shows an analysis of pollutants related

to AMD and ARD pollution. Seasonal changes

were measured, during dry and wet seasonsthrough several years. From these, it was observed

that pollutants were present every season

measured, and that these pollutants are related to

acidic pH and negative SI values. These

conditions indicate the facility of rocks (in zone 1)

and tailings minerals (in zone 2) to dilute and to

liberate pollutants, characteristic of ARD and

AMD, respectively. It is recommended for the

study area, to make physical and geotechnical

tests in soil and tailings samples, in order todesign and to place an impermeable covering on

the surface of the tailings pile, to avoid the

diffusion of the oxygen and rainwater across

tailings, the principal factors that trigger the

oxidation of sulfides. This remediation measure

will only control the AMD, but it is not possible

that controls the ARD.

Acknowledgement

The authors thanks to an anonymous reviewer for

the help in the improvement of this paper.

References

Alpers C.N. and Blowes D. (Eds.) (1994)

Environmental geochemistry of sulfide

oxidation. Boca Raton:ACS Symposium.

Appelo C.A.J. and Postma D. (1999)

Geochemistry, groundwater and pollution.

Rotterdam: Balkema.

Edet A.E., Merkel B. J. and Offiong O. E. (2004

Contamination risk assessment of fres

groundwater using the distribution and chemica

speciation of some potentially toxic elements i

Calabar (southern Nigeria). Environmenta

Geology, 45: 1025-1035.Kimball B.A. (1999): Seasonal variation in meta

concentrations in a stream affected by acid min

drainage, St. Kevin Gulch, Colorado. In

Filipek, L.H., Plumlee G.S. (Eds.), Th

Environmental Geochemistry of Miner

Deposits. Part B: Case Studies and Researc

Topics. Reviews in Economic Geology, vol. 6B

Society of Economic Geologists, Littleton, CO

467-477.

Kim J.J., Kim S.J., Tazaki K. (2002Mineralogical characterization of microbia

ferrihydrite and schwertmannite, and non

biogenic Al-sulfate precipitates from aci

drainage in the Donghae mine area, Korea

Environmental Geology, 42: 19-31.

Kumpulainen S., Carlson L., Risnen M.L

(2007): Seasonal variations of ochreou

precipitates in mine effluents in Finland

Applied Geochemistry, 22: 760-777.

Lizrraga-Mendiola L., Gonzlez-Sandoval M.RDurn-Domnguez M.C. & Mrquez C. (2008

Geochemical behavior in a Zn-Pb-Cu minin

area in the State of Mexico (Central Mexico

Environmental Monitoring and Assessmen

Vol. 155(1): 355-372. DOI 10.1007/s10661

008-0440-1. ISSN 0167-6369 (Printed), 1573

2959 (Online).

Parkhurst, D.L. Appelo, C.A.J. (1999): User

Guide to PHREEQC (Version 2)-A compute

program for speciation, batch-reaction, one

dimensional transport, and inverse geochemica

calculations. Water Resources Investigation

Report 99-4259.

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metal retention through the schwertmannite t

goethite transformation as observed in a fiel

settings, Alta Mine, MT. Applied Geochemistry

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(2005): Factors controlling tungste

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J. P., von Brmssen M. (2004): Behavior of

arsenic and geochemical modeling of arsenic

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Yu J.Y., Heo B. (2001): Dilution and removal o

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1041-1053.


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ABSTRACT The slope stability analysis of lined waste containment system embankment is done usingwedge analysis to find out the minimum factor of safety and the critical surface. The above procedure can bedone by trial and error or by using the concept of optimization problem. Nevertheless, for design of

embankment of waste containment system, use of very elaborate optimization method is not required.Keeping this in view, in this paper a spread sheet based optimization tool has been used to select the critical

failure surface and the minimum factor of safety.

INTRODUCTIONThe stability of slopes of waste containment

systems is one of the most important parameter for

the design of waste containment system, like

hydraulic conductivity of clay liner (Sharma &

Reddy 2004). The stability of slopes needs to be

considered both for with and without seismic

condition. The observation of down-slope

movement in landfills during the Loma Prieta

(1989), Northridge (1994), and Nisqually (2001)

earthquakes is of major concern for the design of

waste containment system. The factor of safety of

1.5 is considered without seismic load and withseismic load FOS of 1.1 is found to be satisfactory.

Though different dynamic analysis are also in use

for the analysis and design of slope of waste

containment system, limit equilibrium method

using pseudo-static is still most popular due to its

simplicity and reliability. As limit equilibrium

method does not consider the magnitude of the

displacement of the slope, the method cannot find

out the structural failure due to sum of all

displacements. However, it is assumed that takinga FOS of 1.1, provides a degree of certainty that

slope is sufficiently stable and permanen

displacement will not occur as the yiel

acceleration will not exceed. If the FOS is les

than 1.0, then seismic deformation analysis will b

required to find out the permanent deformation.

The commonly used limit equilibrium methods ar

an upper bound type of solution as per lim

analysis. In the stability analysis of slopes, it

usual to assume that for practical purposes th

problem can be considered as two dimensional. I

the limit equilibrium method only the concept o

statics is applied. Slope stability problem

however is in general statically indeterminate. A

a result, some simplifying assumptions are to b

made so that unique factor of safety can b

evaluated. The differences between various limequilibrium methods of analysis relate to th

assumptions that are made in order to achiev

statically determinacy and the particula

conditions of equilibrium that are satisfied. Th

shape of the potential slip surface may be qui

irregular depending on the homogeneity of th

slope material. This is particularly true in natur

slopes where joints and fractures dictate th

locations of the failure surface. If some planes o

weakness exist, most critical slip surface wiprobably be a series of planes passing through th

Slope Stability Analysis of Lined Waste Containment System

Embankment Using A Simple Optimization Tool

SARAT KUMAR DAS

National Institute of Technology Rourkela, India ([email protected])

Manas Ranjan Das

ITER, SOA University, Bhubaneswar, India ([email protected])Rajanikanta Biswal

School of Technology, KIIT University, India ([email protected])


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weak strata. In some cases, a combination of plane,

cylindrical, and other irregular failure surfaces

may also exist (Huang, 1983).

The slope stability analysis of lined waste

containment system embankment are done using

wedge analysis, mostly with single or two wedgeto find out the minimum factor of safety and the

critical surface. The above procedure can be done

by trial and error or by using the concept of

optimization problem. The analysis of the

optimization problem can be considered in two

stages: (i) development of objective function and

(ii) application of suitable optimization technique

in solving the objective function. Although the

optimization techniques in geotechnical

engineering is being used since 1960s still it isbeing used in large offices and projects due to

expensive software and the skill required for the

same. However, it is important that the

optimization schemes should be affordable and

simple to be followed by the professional

engineers. Nevertheless, for design of

embankment of waste containment system, use of

very elaborate optimization method is not required.

Keeping this in view, in this paper a three wedge

failure surface is considered and a spread sheetbased optimization tool has been used to select the

critical failure surface and the minimum factor of

safety. Charts for factor of safety based on the

above parameters have been presented for ready

references.

METHODOLOGY

The development of limit equilibrium as

optimization problem is straight forward,

consisting of (i) development of objective function

and (ii) selection of optimization technique.

Development of objective function is based on

different stability analysis method and shape

(circular, wedge and noncircular) of the sliding

mass the slope. In design, the shape of the

unknown slip surface is generally assumed while

the location is determined by some trial and error

procedure. The wedge type of slip surface is more

appropriate for slopes, where critical potential slip

surface includes a relatively long linear segment

through a weak material bounded by stronger

material. A relatively strong levee embankmen

founded on weaker, stratified alluvial soils and th

cover to a lined waste containment system ar

common example of such slopes (Huang 1983).

Development of objective function

In the present study, the three-wedge method fostability analysis of slopes (Huang, 1983) is use

for the development of objective function. This

a force equilibrium method and development o

the equations used for the analysis is described i

details in Huang (1983). Figure 1 shows a typic

geometry for the three-wedge slope failure.

consists of active wedge, passive wedge and

central wedge. Figure 2 shows the free bod

diagram for the three wedge method.

Figure 1Typical three-wedge failure surface of a slop

Figure 2 The free-body diagram for three-wedge

method

The details about the formulation and th

governing equations have been elaborated i

Huang (1983) and Das (2005). The optimizatio

method may be described as finding out th

minimum factor safety which in mathematic

programming form it can be written as:


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MinF:Subjected to

.033cos3

sincos3sin3cos)21(

WsCT

WurNdPP

(1)

The variables (design vectors) are l1, l2, l3,

and F and the application dependant

input parameters are slope angle (),cohesion(ci),height of slope (H), angle of internal friction

(pore pressure parameter(ru) and seismicacceleration coefficientCs..As per physically condition it is found that the

direction of the Ti should be positive (Huang,1983), and the kinematical conditions are applied

for the geometry of the failure surface. tan/3cos32cos21cos1 Hlll (2)

Hlll 3sin32sin21sin1 (3) 1 (4)

Ti 0.0; i= 1,2,3 (5)

The above optimization problem is implemented

using solver of MS Excel. Figure 3 shows the pre-

processing with necessary inputs/ parameters for

the slope and optimization box in the inset. Thetarget cell to be minimized is selected in Set

Target Cell, then it is clicked for Min, the

variable like the geometry of length and angle ofwedges are selected for Guess. The necessary

constraints are added one by one by the command

Add and then it is clicked Solve to find out theoptimum value.

Fig.3 Optimization model using Microsoft Excel

showing the pre-processing

Figure 4 shows the optimized value with the

window Solver Results in the inset. The

sensitivity analysis results also can be displaye

by the command sensitivity

Fig.4 Optimization model using Microsoft Exc

showing the optimized values

RESULTS AND DISCUSSIONThe three wedge stability analysis ar

implemented for different example problems usin

the above methodology. Table 1 presents

comparison of the results of a slope with heigh

12m, cohesion c 15kN/m2, slope angle 450 an

angle of internal friction () as 250 using genet

algorithm (Das 2005) and present method. It ca

be seen that results are comparable with seism

case and more for without seismic coefficien

This variation is expected as a generalized reduce

gradient optimization algorithm used in MSExc

is a initial point dependent (Deb 1995).

TABLE 1 Comparison of factor of safety (FOS

using GA and the present method

Examples Cs FOS

using

GA

FOS

(Present

method)

1 0.00 1.202 1.552

2 0.10 1.060 1.066

3 0.16 1.000 1.000

The method is applied to other examples wit

seismic coefficient (Cs) values of 0.1, 0.16, 0.2

and 0.32 keeping in mind the seismic coefficien

for corresponding to earthquake zones, II, III, I

and V as per Indian standard for Earth quak

design of structure IS: 1893(2002).

Das, Das and Biswal 52




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Fig.5 Variation of factor of safety with C/H for

different seismic zones of India.

Figure 5 shows the variation of FOS with C/H

for different seismic coefficient (zones), for a

slope angle of 300and value of 300. As expected

with increase in C/H the FOS increases anddecreases with increase in Cs values. Similar

charts can be prepared for other values of slope

angle and values. As discussed previously the

FOS should be more than 1.1 with seismic loads,

it was observed that all the slopes with C/H >

0.1 are safe.

Fig.6 Variation of factor of safety with slope angle ()

for different seismic zones of India.

Similarly for C/H, the variation of FOS with

different slope angle in different seismic zone is

shown in Fig. 6. As expected the FOS decreases

with increases in slope angle and seismic

coefficient. So a design office can generate such

ready to use charts for most possible cases of

C/H, and .

CONCLUSIONS

This paper presents determination of factor o

safety of slopes of waste containment system

using three wedge method in conjunction with

simple optimization tool based on spread shee

based software. It was found that the method

efficient in finding out the factor of safety witgood precision. Few charts are presented to fin

out the factor of safety for different seismic zone

of India.

REFERENCES

Das S.K. (2005) Slope stability analysis usin

genetic algorithm Electronic Journal geotechnical Engineering, Vol. 1.

Deb K. (1995) Optimization for EngineerinDesign Algorithms and Examples, PrenticHall of India Pvt. Ltd., New Delhi,.

Huang Y.H. (1983) Stability analysis of slopeVan Nostrand Reinhold Company, USA.

IS 1893: 2002 Criteria for earthquake resistadesign of structures: Part1 general provisionand buildings, Bureau of Indian Standards NeDelhi, India.

Jade S. and K.D. Shanker (1995) Modelling slope failure using a global optimizatiotechnique, Engineering Optimization, Vol. 2No.2, pp. 255-266.

Sharma, H.D. and Reddy K.R.(200

Geoenvironmental Engineering: SiRemediation, Waste Containment and EmerginWaste Management Technologies, John Wile& Sons, Inc., Hoboken, New Jersey.


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Gainful Use of Solid Industrial Wastes as Resource Geo-Material for

Embankment Construction

A.Ghsoh

Scientist, Central Building Research Institute, Roorkee, Uttarkhand, India,([email protected])

S.K.JainScientist, Central Building Research Institute, Roorkee, Uttarkhand, India,([email protected])

Dalip KumarTechnical officer, Central Building Research Institute, Roorkee, Uttarkhand, India,([email protected])

Anand Singh Kalura and Shaifaly SharmaProj. asstt. Central Building Research Institute, Roorkee, Uttarkhand, India,

([email protected])

ABSTRACT Amongst the various solid industrial wastes Ash, and Redmud are generated in huge

quantities. Ash generally is mixed with water and is discharged in the form of slurry in the settlingpond. The waste settles through the sedimentation process in the pond. The excess water isdecanted out of the pond and recycled. Red mud is disposed off through dumpers in the red mud

pond which flows like a viscous fluid by gravity in the pond. Investigations were carried out toexplore the possibility of utilising these wastes as resource geo-material for civil engineering

constructions. In this paper utilisation of ash, and red mud has been discussed.

INTRODUCTION

With the industrialisation the country is producinga variety of waste materials which are rejected by

the industries due to the lack of proper utilizationtechnology. Two major wastes e.g Ash from thethermal power plant and Redmud from the

aluminum plant has been gainfully utilized for civil

engineering construction purposes. The utilizationis briefly described below.

ASH UTILISATIONGeneration of ever increasing quantities of ash, as a

result of combustion of coal, poses serious threat tothe eco-system. Dumping, disposal and utilisationof growing tonnage of this waste from thermal

power plants, commonly known as Flyash, is achallenging task particularly as not more than 5

percent of it has been put to gainful use in thecountry till 1993 94 which was increased to 15%

as result of concerted efforts [Kumar et al (2001)].Recently due to the use of flyash to produce PPC

the utilisation of ash has gone up to nearly 30%

However for civil engineering purposes ash coube used as:

1. Backfill material2. Material for construction of embankme

or road etc

3. Abandoned ash pond could be reclaimfor human habitation purposes.

Reclamation Of Abandoned Ponds For Huma

SettlementsMost of the flyash is disposed off in special

designed ash ponds, which are subsequentabandoned. This has resulted in the growth ofnumber of ash ponds in the vicinity of therm

power plants and in some cases close to urbsettlements. According to a recent estimate, ov

1,00,000 acres of land is required for flyadumping over a span of 30 years to cope with t

present flyash generation rate of 110 million toannually.

A.Ghosh


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Previous workAbandoned flyash ponds have no monetary value.In view of the urban sprawl, several of these

abandoned pond sites have adequate potential fordevelopment for human habitation. Such approachwould also bring about an overall development of

the area with added advantages of conservation ofland resources and abatement of pollution hazards.

It is reported that Ballisager et al

(1981),Havukainen (1983), Ueshita et al (1990)flyash ponds have been used for various uses like

parking lots, grazing fields, play grounds includinggolf courses, picnic spots etc. However, practicallyno example is known to exist indicating the

reclamation of flyash disposal sites for humansettlement. In India, isolated examples are

available where attempts have been made for theconstruction of small structures over ash fills.Aforestation has also been attempted over such fills

to develop green belt.

Demonstration siteCouple of abandoned ash ponds were visited anddiscussions were held with owner of such ponds.Finally, for the construction of demonstration

dwelling units abandoned ash pond at National

Fertilisers Ltd, Panipat was selected.

Methodology

Samples of flyash from different profiles andlocations from the site were collected for laboratory

evaluation.

(a) Laboratory study- Engineering Properties

Direct shear test

Grain size analysis test

Proctor density test Attreberg's Limit test

(b) Field study

The exploration program comprising of thfollowing activities were drawn and executed:

Boring through the entire depth of flya

plus about 3m in the virgin soil.

Standard Penetration Test. Dynamic Cone Penetration Test.

Open pit excavation. Plate Load Test. Full scale foundation test.

Studies for spatial variability

Panipat Ash Pond Site Field Tests

Three Dynamic Cone Penetration Tests (DCPTwere carried out. The minimum and maximuvalue of the same varies between 3 to 15

3-slurry ponds, ash, tailings and dredged sediments

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