Geotechnical properties and Geotechnical properties and stress-strain-time behavior evaluation stress-strain-time behavior evaluation of industrial waste deposits in Bulgariaof industrial waste deposits in Bulgaria

by Prof. D-r Eng. Trifon Germanovby Prof. D-r Eng. Trifon Germanov

Department of GeotechnicsDepartment of Geotechnics

This report presents the results from some recent This report presents the results from some recent studies elaborated under supervision of the author. Part studies elaborated under supervision of the author. Part of the results under consideration are reported on theof the results under consideration are reported on the Main Session 1 - “Man Made deposits - recent and Main Session 1 - “Man Made deposits - recent and ancient” of theancient” of the 1313thth European Conference on Soil European Conference on Soil Mechanics and Geotechnical Engineering, Prague, 2003Mechanics and Geotechnical Engineering, Prague, 2003.

• The results presented in this report are published in the The results presented in this report are published in the Proceedings of the Conference as followed: Proceedings of the Conference as followed:

• Germanov, T. Germanov, T. (2003).(2003). ““Geotechnical properties of Geotechnical properties of industrial waste deposits in Bulgariaindustrial waste deposits in Bulgaria”. Proceeding XIII”. Proceeding XIIIthth European conference on SMGE, Prague, Vol.1, pp. 93-101.European conference on SMGE, Prague, Vol.1, pp. 93-101.

Germanov, T. Germanov, T. (2003).(2003). “ “Limit states (Stability, Limit states (Stability, deformation, erosion….)”deformation, erosion….)”.. Proceeding XIII Proceeding XIIIthth European European conference on SMGE,conference on SMGE, Prague, Vol.3, pp. 119 - 125. Prague, Vol.3, pp. 119 - 125.

Basic considerationBasic consideration The stability of waste deposits, such as tailings dam, landfill, waste The stability of waste deposits, such as tailings dam, landfill, waste

banks and other depends on the mechanical properties of the waste banks and other depends on the mechanical properties of the waste materials and the shape of the deposit’s body. materials and the shape of the deposit’s body.

The basic principles of soil mechanics are usually used for the The basic principles of soil mechanics are usually used for the purpose. On the other hand, the materials included in the waste purpose. On the other hand, the materials included in the waste deposits often have an unusual behavior, different from natural soils. deposits often have an unusual behavior, different from natural soils.

This circumstanceThis circumstance requires a comprehensive program for laboratory requires a comprehensive program for laboratory and in situ study for determination of the real mechanical properties and in situ study for determination of the real mechanical properties of the waste materialsof the waste materials

Summarizing the problems, related to the stability of waste deposits, Summarizing the problems, related to the stability of waste deposits, the following limit states could be considered:the following limit states could be considered: slope stability analysis,slope stability analysis, bearing capacity, bearing capacity, subgrade settlement and differential surface settlement, subgrade settlement and differential surface settlement, erosion (internal and surface).erosion (internal and surface).

Basic considerationBasic consideration

The slope stabilityThe slope stability analysisanalysis is very important problem, is very important problem, mainly for the tailings dams and landfills, where a slope mainly for the tailings dams and landfills, where a slope failure under gravity and filtration efforts is possible. failure under gravity and filtration efforts is possible. Depending on the type of the project, different design Depending on the type of the project, different design methods are used. If the type of the slip surface is accepted, methods are used. If the type of the slip surface is accepted, conventional (based on the Bishop, Jnbu or Spencer conventional (based on the Bishop, Jnbu or Spencer principles) methods could be applied.principles) methods could be applied.

ErosionErosion is important problem in the case of tailings, ash or other dams built up of fine-grained materials where, after raining, a surface slope failure is possible.

The most parts of the industrial waste deposits are in water-saturated conditions. By this reason, the effect of the pore pore water pressurewater pressure should be taken into account evaluating the deposit stability.

Part 1. Part 1.

Geotechnical Properties of Geotechnical Properties of some industrial waste deposits some industrial waste deposits

in Bulgariain Bulgaria

IntroductionIntroduction The design of geotechnical works related to encapsulation The design of geotechnical works related to encapsulation

and stability analysis of industrial waste deposits requires and stability analysis of industrial waste deposits requires the the determination of real physical and mechanical properties determination of real physical and mechanical properties of the waste material. of the waste material.

The Soil Mechanics principles are usually used for this The Soil Mechanics principles are usually used for this purpose. purpose.

However, taking into account the specific features of the However, taking into account the specific features of the waste materials (short time of deposit, usually uniformly waste materials (short time of deposit, usually uniformly grain size distribution, great grain size distribution, great ability for ability for deformation), some deformation), some deviations from the standard methods for soils testing are deviations from the standard methods for soils testing are possible. possible.

During the last 10-15 years an intensive program for During the last 10-15 years an intensive program for construction works related to the environmental protection construction works related to the environmental protection in Bulgaria has started. in Bulgaria has started.

Part of this program is related to designing of Part of this program is related to designing of equipment with the purpose to encapsulation equipment with the purpose to encapsulation and remediation of industrial waste deposits. and remediation of industrial waste deposits.

The laboratory of Soil and Rock Mechanics at The laboratory of Soil and Rock Mechanics at the University of Architecture, Civil the University of Architecture, Civil Engineering and Geodesy took part in these Engineering and Geodesy took part in these programs, mainly conducting laboratory programs, mainly conducting laboratory testing for determination of geotechnical testing for determination of geotechnical properties of waste materials. properties of waste materials.

IntroductionIntroduction

IntroductionIntroduction

Only part of the results from laboratory testing is Only part of the results from laboratory testing is presented in the here. presented in the here.

Three projects, , developeddeveloped under supervision of the under supervision of the author are consideredauthor are considered: :

Encapsulation of “Blue lagoon”;Encapsulation of “Blue lagoon”; Encapsulation of the oxidative pond near the town of Encapsulation of the oxidative pond near the town of

Burgas;Burgas; Stability analysis of “Liuliakovitsa” tailings dam.Stability analysis of “Liuliakovitsa” tailings dam. The waste deposits, under consideration, are situated in The waste deposits, under consideration, are situated in

different part in Bulgaria. different part in Bulgaria.

Encapsulation of “Encapsulation of “Blue LagoonBlue Lagoon”” The slime pond (called “The slime pond (called “Blue Lagoon”) is situated on the territory ”) is situated on the territory

of the Pirdop Copper Metallurgical Plant located some 70 km to of the Pirdop Copper Metallurgical Plant located some 70 km to the east of Sofia. Industrial activities on this site started in the late the east of Sofia. Industrial activities on this site started in the late 1950’s. 1950’s.

The Blue Lagoon designates the settling pond, which contains the The Blue Lagoon designates the settling pond, which contains the calcium arsenic precipitate (slime) coming from the copper calcium arsenic precipitate (slime) coming from the copper metallurgical plant. metallurgical plant.

The northern edge of the Blue Lagoon is rather close to the Sofia-The northern edge of the Blue Lagoon is rather close to the Sofia-Burgas railway.Burgas railway.

The initial slime pond was constructed in 1956, mostly on the The initial slime pond was constructed in 1956, mostly on the original sloping (~ 3.5%) ground surface of alluvial soil with a original sloping (~ 3.5%) ground surface of alluvial soil with a high clay content which is underlain by gneiss bedrock. high clay content which is underlain by gneiss bedrock.

The elevation of the bedrock surface is variable. The elevation of the bedrock surface is variable.

Drill holes advanced to either establish the Drill holes advanced to either establish the depth to be more than 20 m below the depth to be more than 20 m below the ground surface. ground surface.

The slime surface has an area of about 9.6 The slime surface has an area of about 9.6 ha and the greatest depth, in 1997 was ha and the greatest depth, in 1997 was 12.70 m below the slime surface12.70 m below the slime surface. .

The estimated total volume of the stored The estimated total volume of the stored sediments (slime) was about sediments (slime) was about 600 000 m600 000 m33..

Encapsulation of Encapsulation of “Blue Lagoon”“Blue Lagoon”

Encapsulation of the oxidative pond near BurgasEncapsulation of the oxidative pond near Burgas

The The oxidative pond is situated near the quarter “Meden is situated near the quarter “Meden Rudnik” (Cooper mine) in the town of Burgas. Rudnik” (Cooper mine) in the town of Burgas.

To the west the pond is bounded by “Mandra” dam. At first, To the west the pond is bounded by “Mandra” dam. At first, the pond had been used as a settling basin for water supply.the pond had been used as a settling basin for water supply.

During 1984 it was taken out from the scheme of the water During 1984 it was taken out from the scheme of the water treatment and had been used as a site for deposit of floating treatment and had been used as a site for deposit of floating refuse products from cleaning of the other oxidative ponds.refuse products from cleaning of the other oxidative ponds.

During 1991 the free filling of the pond by mixture of During 1991 the free filling of the pond by mixture of constructionconstructionss refuses, sediments and ash from the ovens for refuses, sediments and ash from the ovens for burning of petroleum and biological sediments began. As a burning of petroleum and biological sediments began. As a result of this, an area of result of this, an area of 298 ha was filled298 ha was filled. .

Thus, the oxidative pond was formed of three parts: filled Thus, the oxidative pond was formed of three parts: filled bodybody ( (swamp), settled lake, and slime field.swamp), settled lake, and slime field.

““Liuliakovitsa” tailings dam stability analysisLiuliakovitsa” tailings dam stability analysis The tailings dam “Liuliakovitsa” is a part of the The tailings dam “Liuliakovitsa” is a part of the Assarel Assarel

cooper flotation plantcooper flotation plant, designed with an improved , designed with an improved construction. construction.

Its final height will be 190 mIts final height will be 190 m. The starter dam, built of . The starter dam, built of draining rock fill, has a tongue-shaped projecting lower draining rock fill, has a tongue-shaped projecting lower upstream part. The length of this part is equal to the upstream part. The length of this part is equal to the distance from the starter dam to the decant pond at the distance from the starter dam to the decant pond at the initial stage. It is calculated to ensure stability of the tailings initial stage. It is calculated to ensure stability of the tailings dam at its final height. dam at its final height.

The coarser fractions are laid off in the supporting part over The coarser fractions are laid off in the supporting part over the tongue, and the finer material is washed off into the the tongue, and the finer material is washed off into the pond. pond.

This kind of sorting makes it possible to use the good This kind of sorting makes it possible to use the good strength of the coarse tailings deposited over the tong, as a strength of the coarse tailings deposited over the tong, as a substitute of the rockfill. substitute of the rockfill.

The construction of the starter dam began late in The construction of the starter dam began late in 1984, and the deposition of the tailings started in 1984, and the deposition of the tailings started in 1990. 1990.

Preliminary study for determination of consolidation Preliminary study for determination of consolidation characteristics of the tailings, obtained in laboratory, characteristics of the tailings, obtained in laboratory, was carried out in 1987. was carried out in 1987.

Nowadays, the height of tailings dam reaches to 130 mNowadays, the height of tailings dam reaches to 130 m

Thus, supporting starter dam of rockfill Thus, supporting starter dam of rockfill with a lower-than-usual height is used.with a lower-than-usual height is used.

““Liuliakovitsa” tailings dam stability analysisLiuliakovitsa” tailings dam stability analysis

Methodology of the laboratory testingMethodology of the laboratory testingWaste materials samplingWaste materials sampling The aim of samplingThe aim of sampling is to obtain samples for identification of is to obtain samples for identification of

the waste materials as well as to perform laboratory testing the waste materials as well as to perform laboratory testing for determination of the geotechnical properties. for determination of the geotechnical properties.

The techniques used for sampling depend on the in-situ The techniques used for sampling depend on the in-situ conditions of the settled waste materials. conditions of the settled waste materials.

Different methods for sampling are applied.Different methods for sampling are applied. The drilling works in the The drilling works in the Blue Lagoon were done according

to preliminary elaborated pattern of borehole net, consisting of 32 drillings, with dimensions of gird 50m to 50 m.

A floating caisson/pontoon was used. A floating caisson/pontoon was used. Sampling was done through an opening in the center of the Sampling was done through an opening in the center of the

pontoon by means of a pipe-drilling device of 2.5 inches, pontoon by means of a pipe-drilling device of 2.5 inches, internal diameter, with jointed sections of 100 cm each. internal diameter, with jointed sections of 100 cm each.

Waste materials samplingWaste materials sampling

During the process a total of 220 m have been drilled During the process a total of 220 m have been drilled and 225 samples were taken.and 225 samples were taken.

The samples for laboratory study were delivered in The samples for laboratory study were delivered in liquid condition using plastic bottles. liquid condition using plastic bottles.

Before the beginning of the official program of Before the beginning of the official program of laboratory geotechnical study, several laboratory geotechnical study, several methodological compression tests were carried out. methodological compression tests were carried out.

A similar methodology has been applied for has been applied for sampling of the refuse materials from the sampling of the refuse materials from the oxidative oxidative pond.pond.

Preliminary methodological compression tests of the slime Preliminary methodological compression tests of the slime from “from “Blue LagoonBlue Lagoon””

Two bottles with slime, taken from 0,5m and 4,5m depth Two bottles with slime, taken from 0,5m and 4,5m depth were used for the purpose. Both samples have were used for the purpose. Both samples have approximately uniform initial density and water approximately uniform initial density and water content. content.

The following initial characteristics for the sample from The following initial characteristics for the sample from 4,5m depth are determined:4,5m depth are determined:

water content water content WWn0n0=205,6%; =205,6%;

wet density wet density n0n0=1,185 g/cm=1,185 g/cm33;;

dry density dry density d0d0=0,397 g/cm=0,397 g/cm33; ;

void ratio void ratio ee00=5,73;=5,73;

degree of saturation degree of saturation SSrr =1,00. =1,00.

Initial identification characteristics of the Initial identification characteristics of the refused materials form the refused materials form the oxidative pondoxidative pond

The refuse materials have a large quantity of The refuse materials have a large quantity of petroleum products. petroleum products.

To decrease the effect of these products on the To decrease the effect of these products on the geotechnical properties, a special procedure was geotechnical properties, a special procedure was applied.applied.

At first, the refuse materials have been laid on a At first, the refuse materials have been laid on a filter paper and rest one day to free drying. filter paper and rest one day to free drying.

After drying in the oven at a temperature of After drying in the oven at a temperature of 50 - 60 50 - 60 СС00 and after free settling, the refuse materials and after free settling, the refuse materials showed approximately showed approximately 70% soil particles and 30% 70% soil particles and 30% organicorganic contentscontents. .

The The identification geotechnical characteristics in identification geotechnical characteristics in “natural conditions“natural conditions” are evaluated according to ” are evaluated according to standard methods as follows: standard methods as follows:

the bulk density in by means of direct filling of the the bulk density in by means of direct filling of the refuse materials in the oedometers; the water refuse materials in the oedometers; the water content - drying the samples at a temperature of content - drying the samples at a temperature of 50 50 - 60 С- 60 С00; ;

grain size distribution – by grain size distribution – by sieve and areometric sieve and areometric analysis. analysis.

The average characteristics are given in The average characteristics are given in Table 1..

Initial identification characteristics of the Initial identification characteristics of the refused materials form the oxidative pondrefused materials form the oxidative pond

Characteristics Settledlake

Slimefield

Swamp

1. Specific gravity s g/cm3 1.354 1.427 1.437

2. Bulk density n g/cm3 0.983 0.985 0.930

3. Water content w % 580 237 2794. Dry density

d g/cm3 0.145 0.292 0.2455. Void volume n - 0.892 0.795 0.8276. Void ratio e - 8.335 3.879 4.8117. Degree of saturation Sr - 0.941 0.871 0.826

Basic physical characteristics of the refuse materials Basic physical characteristics of the refuse materials from the from the oxidative pond

Basic physical characteristics ofBasic physical characteristics of tailings materialstailings materials

Characteristics From To1. Specific gravity

s g/cm3 2.68 2.782. Bulk density

n g/cm3 1.53 2.063. Water content w % 4.9 32.04. Dry density

d g/cm3 1.32 1.785. Void volume n - 0.366 0.5286. Void ratio e - 0.525 1.127. Degree of saturation Sr - 0.53 0.998. Grain size distribution

Sand % 14 64 Silt % 36 80 Clay % 13 22

Determination of the mechanical propertiesDetermination of the mechanical properties

Oedometric testsOedometric testsTwo types of oedometer have been used for Two types of oedometer have been used for

compression testscompression tests:: Oedometer Oedometer without friction along the circular area along the circular area

of the sample for long term consolidation tests with of the sample for long term consolidation tests with one side vertical drainage.one side vertical drainage.

ELE Rowe type consolidation cells for compression tests with radial inwards drainage

The The oedometric tests of the tailingsoedometric tests of the tailings were carried out were carried out directly by using undisturbed samples.directly by using undisturbed samples.

Oedometric tests - “Blue Lagoon”Oedometric tests - “Blue Lagoon” Taking into account that it is impossible to take

undisturbed samples of the slime and refused material from pond “Blue Lagoon” and “Oxidative pond” and after the conclusion that there is not great variation of the unit weight with depth, a non-standard procedure was applied for preparation of samples for all oedometric tests.

According to the approximate evaluation of density of samples, measuring the cell volume, the required mass of the natural slime and refused materials (mixture from 3-4 bottles) was measured.

This mass is put into the cell, compacted uniformly, on 4 - 6 layers

Oedometric tests - resultsOedometric tests - results Time - deformation properties are determined by using time-Time - deformation properties are determined by using time-

deformation curves in “log scale”deformation curves in “log scale” mainly mainly. The coefficients of . The coefficients of consolidation consolidation CCvv are computed applying Casagrande’s method. are computed applying Casagrande’s method.

The creep indexes The creep indexes CCaeae (coefficients of secondary consolidation) (coefficients of secondary consolidation)

are computed by using formula: are computed by using formula: CCaeae = (1 + e = (1 + e00)e)eaa,, where:where: ee00-- initial void rationinitial void ration;; eeaa - - coefficient of coefficient of

secondary compression. secondary compression. Initial times of creeping, Initial times of creeping, tt00, are computed from the log-time-, are computed from the log-time-

settlement curves. settlement curves. The coefficients of radial consolidation The coefficients of radial consolidation CCriri are computed by are computed by

using square-root time curves according to using square-root time curves according to BS 1377BS 1377. . The average compression and consolidation characteristics are The average compression and consolidation characteristics are

presented in presented in Table 3..

Triaxial tests - resultsTriaxial tests - results Triaxial shear tests were carried out only with slimes and Triaxial shear tests were carried out only with slimes and

tailings samples. tailings samples. The following types of triaxial shear tests are performed: The following types of triaxial shear tests are performed:

undrained-unconsolidated (UU) and consolidated undrained undrained-unconsolidated (UU) and consolidated undrained (CU) tests, with pore pressure measurement.(CU) tests, with pore pressure measurement.

After preparation of the specimen, each triaxial shear test is After preparation of the specimen, each triaxial shear test is carried out following the standard procedures according to carried out following the standard procedures according to standards (standards (ASTM D 280-95 and NF P 94-070ASTM D 280-95 and NF P 94-070, October 1994). , October 1994). Each shear strength parameter is determined using four Mohr Each shear strength parameter is determined using four Mohr circles. circles.

The results from UU and CU tests are presented by following The results from UU and CU tests are presented by following relationships: deviator stress-axial strain, pore pressure relationships: deviator stress-axial strain, pore pressure increment – axial strain and relations increment – axial strain and relations t = f(t = f(ss)) and and tt’ = f(’ = f(ss’) ’) [[tt’=(’=(11--33)/2; )/2; ss=(=(11++33)/2; )/2; ss’=(’=(''11++''33)/2)/2].]. Average results from Average results from

triaxial shear tests are presented in triaxial shear tests are presented in Table 3.

Basic deformation and strength characteristicsBasic deformation and strength characteristics

Characteristics Bluelagoon

Oxidativepond

Tailingsdam

1. Initial void ratio e - 7.45 10.27 0.8252. Preconsolidation pressure ’p kPa 8 10 20.03. Compression index Cc - 1.501 0.553 0.07334. Swell index Cs - 0.157 0.285 0.0055. Oedometric secant modulus Eoed kPa 560 415 140006. Oedometric elastic modulus E kPa 4630 1250 454507. Coef. of vertical consolidation Cv 10-6m2/s 6.05 0.165 0.968. Coef. of radial consolidation Cri 10-6m2/s 4.4 3.036 0.0769. Creep index Ce - 0.0205 0.0128 0.0016

10. Initial time of creeping t0 min 420 1450 205

11. Undrained shear strength cu kPa 32 - -12. Effective cohesion c kPa 12 - 1513. Effective angle of int.friction degree 25 - 21

Part 2.Part 2.Stress-strain-time behaviorStress-strain-time behavior

evaluationevaluation

The effect of the pore water The effect of the pore water pressure on the stress-strain pressure on the stress-strain

behaviorbehavior

Basic constitutive equations for the pore Basic constitutive equations for the pore water pressure evaluationwater pressure evaluation

Following Germanov (2000), the massifs of saturated waste Following Germanov (2000), the massifs of saturated waste materials could be considered as multi-phase medium and their materials could be considered as multi-phase medium and their stress-strain behavior being accompanied by two simultaneous, stress-strain behavior being accompanied by two simultaneous, rheological processes: filtration and creeping. rheological processes: filtration and creeping.

It is assumed that the deformation of the soil skeleton could be It is assumed that the deformation of the soil skeleton could be presented according to the theory of linear creep by the equation:presented according to the theory of linear creep by the equation:

t

vv dtmK

ttmK

ttee

1

),()(1

1),(

21

)()(

000

where: where: ee00 and and ee((tt)) are the initial and variable over time void ratios; are the initial and variable over time void ratios; (t)(t) is the sum of normal effective stresses at a fixed point of the soil is the sum of normal effective stresses at a fixed point of the soil massifs; massifs; KK00 is the coefficient of the lateral pressure at rest; is the coefficient of the lateral pressure at rest; mmvv((t,t,)) is the generalized coefficient of volume strain. is the generalized coefficient of volume strain.

Basic constitutive equations for the pore Basic constitutive equations for the pore water pressure evaluationwater pressure evaluation

)](exp[1)()(),( 0 tmtmv

mm00(()) is the coefficient of instantaneous strain (linear compressibility);is the coefficient of instantaneous strain (linear compressibility); (()) is the function of ageing (tixotropic strengthening) of the soil skeletonis the function of ageing (tixotropic strengthening) of the soil skeleton.

h

l

mm )(

mmll is the coefficient of volume creep strain (secondary compression); is the coefficient of volume creep strain (secondary compression); - the parameter of creeping speed; - the parameter of creeping speed; mmhh - the coefficient of "ageing" strain of the soil skeleton; - the coefficient of "ageing" strain of the soil skeleton; 11 - the parameter of the soil skeleton age (the previous stressed - the parameter of the soil skeleton age (the previous stressed condition). condition). The methods for determining the coefficients of volume strains and The methods for determining the coefficients of volume strains and the creep parameters are developed by thethe creep parameters are developed by the author (see Germanov author (see Germanov 2000). 2000).

Basic constitutive equations for the Basic constitutive equations for the pore water pressure evaluationpore water pressure evaluation

Assuming that the fluid filtration is according to Darcy's Assuming that the fluid filtration is according to Darcy's law, the function law, the function uuww((t,x,yt,x,y)) for two-dimensional consolidation, for two-dimensional consolidation,

is determined by the solution of the following differential is determined by the solution of the following differential equation:equation:

)()()(])[()( 1

2

21212

2

1 tt

att

tfuut

Ct

utf

t

ua wwv

ww

where: where: 11((tt) = ) = yy((tt) + ) + zz((tt););

yy(t)(t) andand zz(t)(t) are the total normal stresses which would be accepted: are the total normal stresses which would be accepted:

constant, when the period of operation is considered; variation with constant, when the period of operation is considered; variation with a constant velocity for the construction period; variation under a constant velocity for the construction period; variation under cyclic loads (machine foundations or earthquake motions).cyclic loads (machine foundations or earthquake motions).

The other coefficients and functions depend on The other coefficients and functions depend on the soil properties.the soil properties.

The author has received an exact solution of the The author has received an exact solution of the one-dimensional consolidation, under one-dimensional consolidation, under corresponding initials and boundaries corresponding initials and boundaries conditions, according to equation (Germanov, conditions, according to equation (Germanov, 1988). Using the finite element method, the two-1988). Using the finite element method, the two-dimensional consolidation has been solved dimensional consolidation has been solved (Germanov, 2000).(Germanov, 2000).

Basic constitutive equations for the Basic constitutive equations for the pore water pressure evaluationpore water pressure evaluation

Liquefaction potential Liquefaction potential evaluation of a tailings evaluation of a tailings

dam dam

Liquefaction potential evaluation of a tailings damLiquefaction potential evaluation of a tailings dam

The increasing of the pore water pressure under static The increasing of the pore water pressure under static and dynamic (seismic) excitation loads may lead to and dynamic (seismic) excitation loads may lead to decrease the effective stresses to zero. decrease the effective stresses to zero.

This phenomenon, known as liquefaction, may provoke This phenomenon, known as liquefaction, may provoke a loss of the bearing capacity and failure of the soil a loss of the bearing capacity and failure of the soil massifs.massifs.

Evaluation of the exceed pore water pressure under Evaluation of the exceed pore water pressure under static loading is performed by using the solutions static loading is performed by using the solutions developed by the author (Germanov, 2000), based on the developed by the author (Germanov, 2000), based on the theory of the two-dimensional consolidation, taking into theory of the two-dimensional consolidation, taking into account the rheological properties of the materials. account the rheological properties of the materials.

Liquefaction potential evaluation of a tailings damLiquefaction potential evaluation of a tailings dam

Liquefaction is a phenomenon in which the strength and stiffness Liquefaction is a phenomenon in which the strength and stiffness of a soil is reduced by earthquake shaking or other rapid loading. of a soil is reduced by earthquake shaking or other rapid loading.

The phenomenon is only generally considered for sandy soils and The phenomenon is only generally considered for sandy soils and usually for loose sands. usually for loose sands.

However, the increase of the pore pressure could reduce the However, the increase of the pore pressure could reduce the effective pressure, not only in fine-grained soils and coarse-effective pressure, not only in fine-grained soils and coarse-grained soils. grained soils.

It was establishedIt was established that that clay or silt with low plasticity index, such clay or silt with low plasticity index, such as tailings material, has been found to be as vulnerable to as tailings material, has been found to be as vulnerable to liquefaction (Ishihara, 1985).liquefaction (Ishihara, 1985).

One of the criteria for liquefaction potential evaluation is the One of the criteria for liquefaction potential evaluation is the grain size distribution. grain size distribution.

The results of the laboratory investigation of the tailings materials The results of the laboratory investigation of the tailings materials from “Liuliakowitsa” tailings dam shows that the investigatedfrom “Liuliakowitsa” tailings dam shows that the investigated tailings could be classified as fine silty sand. tailings could be classified as fine silty sand.

The representative grain-size distribution curves are shown below. It The representative grain-size distribution curves are shown below. It can be seen that the grain size curves can be seen that the grain size curves belong to the boundaries of belong to the boundaries of the the most liquefable soilsmost liquefable soils (Ishihara, 1985). (Ishihara, 1985). This means that in some This means that in some conditions, tailings could reach to a state of liquefaction.conditions, tailings could reach to a state of liquefaction.

0

20

40

60

80

100

0.0010.0100.1001.000

Diameter ( mm)

Per

cen

t fi

ner

by

wei

ght

(%)

Liquefaction potential evaluation of a tailings damLiquefaction potential evaluation of a tailings dam An approximate method based on theoretical evaluation of An approximate method based on theoretical evaluation of

the increase of pore water pressure in tailings dam’s body the increase of pore water pressure in tailings dam’s body during an earthquake is applied herein. during an earthquake is applied herein.

Following Martin & Seed (1978), the basic assumption for Following Martin & Seed (1978), the basic assumption for pore pressure generation and dissipation analysis is that the pore pressure generation and dissipation analysis is that the excess pore water pressure, excess pore water pressure, uuww, in a soil element, could be , in a soil element, could be presented as the sum of the pore water pressure under static presented as the sum of the pore water pressure under static loading, loading, uuw,stw,st, and pore water pressure increment generated , and pore water pressure increment generated under dynamic excitation - under dynamic excitation - uuw,dw,d. .

The static pore water pressure uThe static pore water pressure uw,stw,st could be computed by could be computed by

using a computer program, developed by the author using a computer program, developed by the author (Germanov, 2000) based on the constitutive equations given (Germanov, 2000) based on the constitutive equations given in the paper. in the paper.

The computations are performed, applying The computations are performed, applying nonlinear experimental relations of the physical and consolidation of the physical and consolidation characteristics and expressing their variation with the dam characteristics and expressing their variation with the dam height. height.

A cross section of the tailings dam and in situ measured pore A cross section of the tailings dam and in situ measured pore water pressure are presented below (Kalchev, 2003). water pressure are presented below (Kalchev, 2003).

The computations for static conditions show that there are no The computations for static conditions show that there are no differences between theoretical and in-situ measured values of the differences between theoretical and in-situ measured values of the pore water pressure.pore water pressure.

Nonlinear linear characteristics of Nonlinear linear characteristics of

tailings dam for static analysistailings dam for static analysis

0

10

20

30

40

50

60

70

80

90

100

19.0 19.5 20.0 20.5 21.0 21.5

Unit weight n, kN/m3

Dep

th, m

0

10

20

30

40

50

60

70

0 10000 20000 30000 40000

Compression modulus E oed , kPa

Dep

th, m

Liquefaction potential evaluation of a tailings damLiquefaction potential evaluation of a tailings dam

The dynamic pore water pressure (The dynamic pore water pressure (uuw,dw,d) is computed, ) is computed,

considering the tailings dam, under cycling loading, in considering the tailings dam, under cycling loading, in undrained conditions, by using the expression (Martin & undrained conditions, by using the expression (Martin & Seed 1978):Seed 1978):

2

1

'0, arcsin

2.

ldw N

Nu

where:where: ''00 is the effective overburden pressure;is the effective overburden pressure; NN – the – the

number of uniform stress cycles undergone by the soil number of uniform stress cycles undergone by the soil element;element; NNll – the number of cycles at the same levels – the number of cycles at the same levels

required to reach initial liquefactionrequired to reach initial liquefaction. .

LiquefactionLiquefaction potential evaluation of a tailings dampotential evaluation of a tailings dam

The number of cycles are accepted: The number of cycles are accepted: NN = 12= 12 for an earthquake with for an earthquake with magnitude equal to magnitude equal to 7; 7; NNl l =50=50, according to Germanov & Kostov , according to Germanov & Kostov (1994). The distribution of the pore water pressure at the dam height (1994). The distribution of the pore water pressure at the dam height is presented below.is presented below.The maximum value of pore pressure ratio The maximum value of pore pressure ratio uuww//''00 reaches to 0.8. It is reaches to 0.8. It is obviously, under the stress strain conditions, thatobviously, under the stress strain conditions, that there is no area in there is no area in tailings dam, which would be susceptible to liquefactiontailings dam, which would be susceptible to liquefaction..

0

20

40

60

80

100

120

140

0 200 400 600 800 1000

Pore pressure, kPa

Hei

ght,

m

0

20

40

60

80

100

120

140

0.00 0.20 0.40 0.60 0.80 1.00

Pore pressure ratio uw/ 'v

Hei

ght,

muuw,stw,st

uuw,dw,d

Evaluation of the ultimate stress-Evaluation of the ultimate stress-strain state of the slime pond before strain state of the slime pond before

encapsulationencapsulation

Situation of the “Blue Lagoon” before Situation of the “Blue Lagoon” before EncapsulationEncapsulation

Evaluation of the ultimate stress strain state of the Evaluation of the ultimate stress strain state of the slime pond during encapsulationslime pond during encapsulation

One of the variants of the project for encapsulation of the slime One of the variants of the project for encapsulation of the slime pond “Blue Lagoon” pond “Blue Lagoon” considers establishment of considers establishment of drainage wells drainage wells and filling the pond with granular materials as well as and filling the pond with granular materials as well as

construction of embankment 8 m high.construction of embankment 8 m high. Another variant without vertical drainage is considered as well. It Another variant without vertical drainage is considered as well. It

is supposed that after dewatering the filling will be made is supposed that after dewatering the filling will be made approximate by constant speed. approximate by constant speed.

For evaluation of ultimate stress-strain state the Mohr-Coulomb For evaluation of ultimate stress-strain state the Mohr-Coulomb equation for ultimate equilibrium could be used (Germanov, equation for ultimate equilibrium could be used (Germanov, 1986, 2000). 1986, 2000).

Considering the slime pond in unconsolidated conditions under Considering the slime pond in unconsolidated conditions under embankment’s loads, the dimensions of the so-called "plastic embankment’s loads, the dimensions of the so-called "plastic zones" could be evaluated by using the expression:zones" could be evaluated by using the expression:

Evaluation of the ultimate stress strain state Evaluation of the ultimate stress strain state of the slime pond during encapsulationof the slime pond during encapsulation

''''

22''

cot2

4arcsin

gcyz

zyyz

cr

where,where, zz, , yy andand zyzy, , are effective normal and tangential stresses in are effective normal and tangential stresses in

a given point of the slime pond. a given point of the slime pond. The zones of ultimate equilibrium are defined by the The zones of ultimate equilibrium are defined by the

conditioncondition cr cr >>'' (('-'- effective angle of internal friction). If these effective angle of internal friction). If these zones are relatively large, the subgrade (slime pond) will lost its zones are relatively large, the subgrade (slime pond) will lost its overall stability.overall stability.A computer program for ultimate stress-strain behavior evaluation A computer program for ultimate stress-strain behavior evaluation of saturated soil massifs, taking into account of the pore water of saturated soil massifs, taking into account of the pore water pressure generation and dissipation during construction and pressure generation and dissipation during construction and operation has been developed by the author (Germanov, 1986). operation has been developed by the author (Germanov, 1986).

Evaluation of the ultimate stress strain state of the Evaluation of the ultimate stress strain state of the slime pond during encapsulationslime pond during encapsulation

Some results from computations are given in Some results from computations are given in Table 4Table 4. Two . Two loading steps are considered: q=80 kPa and q=160kPa, loading steps are considered: q=80 kPa and q=160kPa, corresponding to 4.0 m and 8.0 m embankment fill respectively. corresponding to 4.0 m and 8.0 m embankment fill respectively. All computations are performed by using input data (geotechnical All computations are performed by using input data (geotechnical characteristics), according to Germanov (2003).characteristics), according to Germanov (2003).

Z(m)

cr (degree)

for q = 80 kPa

cr (degree)

for q = 160 kPa1. 2 15 252. 4 12 213. 6 10 184. 8 9 155. 10 8 146. 12 7 12

Table 4. Table 4. ccrr values for different deptsvalues for different depts.

For this case (For this case (' ' ),), the the plastic zone could be formed plastic zone could be formed to 6.0m depth at the final to 6.0m depth at the final stage of loadingstage of loading. .

Determination of the time-Determination of the time-depending settlement of the depending settlement of the

Oxidative pondOxidative pond

Determination of the time-depending settlement of Determination of the time-depending settlement of the Oxidative pondthe Oxidative pond

The first stage of The first stage of the the project for encapsulation and remediation project for encapsulation and remediation of the oxidative pond near the town of Burgas, proposes a of the oxidative pond near the town of Burgas, proposes a filling the pond by granular material over geotextile.filling the pond by granular material over geotextile.

The results of the consolidation tests The results of the consolidation tests (Germanov, 2003) (Germanov, 2003) show show some specific features of the petroleum refuses some specific features of the petroleum refuses which which considerably considerably distinguish them from distinguish them from naturalnatural soils. soils.

First of all, First of all, the test results show a very low value of densities the test results show a very low value of densities and very large porosity (and very large porosity (n n 1.0 g/cm1.0 g/cm33; ; e e = 8.0 = 8.0 10.010.0). ).

Water content reaches Water content reaches 500 – 600%.500 – 600%. On the other hand, during the consolidation tests, the On the other hand, during the consolidation tests, the

settlements are developing very slowly over time under small settlements are developing very slowly over time under small loading. loading.

The great part of the secondary consolidation The great part of the secondary consolidation presumes the presumes the presencepresence of rheological processes. of rheological processes.

In order In order то receive то receive a preliminary a preliminary prognosis of timeprognosis of time--depending settlement, a computation was depending settlement, a computation was performed for the subgrade (i.e. petroleum refuses) performed for the subgrade (i.e. petroleum refuses) under loading from embankment 2.0m high. under loading from embankment 2.0m high.

It is accepted that the construction works (time of It is accepted that the construction works (time of filling) will last six months.filling) will last six months.

The degree of consolidation at the end of The degree of consolidation at the end of construction period and during “operation” after construction period and during “operation” after one, two and five years is computed.one, two and five years is computed.

Determination of the time-depending Determination of the time-depending settlement of the Oxidative pondsettlement of the Oxidative pond

Situation of the oxidative pond, slime Situation of the oxidative pond, slime field and swampfield and swamp

Time-depending settlement of the Oxidative pondTime-depending settlement of the Oxidative pond

Table 5. Final settlement and degree of consolidationTable 5. Final settlement and degree of consolidation Cross sections I - I II-II III - III IV - IV V - V Longi-

tudinalMaximum length, m 202 220 160 195 341 550Maximum depth, m 2,10 1.80 1.80 4.20 3.95 4.95Final settlement, cm 27.3 25.1 25.6 76.5 63.9 79.8Degree ofconsolidation, %At the end of filling 16 19 16 14 14 14At the end of thefirst year

24 26 24 22 24 22

At the end of thesecond year

37 39 37 35 35 35

At the end of thefifth year

63 64 63 62 63 61

Determination of the time-depending settlement of Determination of the time-depending settlement of the oxidative pondthe oxidative pond

The results presented in The results presented in Table 5 show a low value of show a low value of the degree of consolidation at the end of filling. the degree of consolidation at the end of filling.

With respect toWith respect to the the homogeneous composition of the homogeneous composition of the petroleum refuses, the computations showed an petroleum refuses, the computations showed an approximately equal degree of consolidation at the approximately equal degree of consolidation at the end of the different periods. end of the different periods.

AAnn increase of the degree increase of the degree of of consolidation could be consolidation could be reached by increasing the reached by increasing the construction period (time construction period (time of filling). of filling).

On the other hand, under this loading, in spite of the On the other hand, under this loading, in spite of the low values of the deformation modulus, the final low values of the deformation modulus, the final settlements are comparatively small – from 25cm to settlements are comparatively small – from 25cm to 78 cm. 78 cm.

Increasing the final settlements Increasing the final settlements could be could be possible by means of additional loads, which, possible by means of additional loads, which, after reaching the predicted settlement, should after reaching the predicted settlement, should be removed. be removed.

The great value of water content supposed The great value of water content supposed compression under static loading only. compression under static loading only.

The influence of the dynamic loading (for The influence of the dynamic loading (for example vibrations) on such type of refuse example vibrations) on such type of refuse materials needs an additional studymaterials needs an additional study..

Determination of the time-depending Determination of the time-depending settlement of the oxidative pondsettlement of the oxidative pond

ConclusionConclusionThe results presented in the presentation The results presented in the presentation

underline the considerable influence of the pore underline the considerable influence of the pore water pressure on the stress-strain behavior of water pressure on the stress-strain behavior of waste deposits which reached a limit state. waste deposits which reached a limit state.

Besides the conventional methods for stability Besides the conventional methods for stability analysis of the saturated waste deposits, analysis of the saturated waste deposits, additional analyse, such as liquefaction, bearing additional analyse, such as liquefaction, bearing capacity and time depending settlements should capacity and time depending settlements should be made. be made.

ReferencesReferences Germanov, TGermanov, T.(1988). .(1988). Creep and ageing effects on stresses and Creep and ageing effects on stresses and

deformations of saturated clayey soils”.deformations of saturated clayey soils”. Proc.Proc. Int. conf. on rheology Int. conf. on rheology and soil mechanics, Coventry, pp 194-203.and soil mechanics, Coventry, pp 194-203.

KaltchevKaltchev (1998). Instrumentation system for Assarel Tailings dam. (1998). Instrumentation system for Assarel Tailings dam. Proc. Green 2. Krakow, pp. 270-272.Proc. Green 2. Krakow, pp. 270-272.

Abadjiev, Germanov, MarkovAbadjiev, Germanov, Markov. (1987).Determination of tailings . (1987).Determination of tailings consolidation for a high spigotted tailings dam. Proc. 9consolidation for a high spigotted tailings dam. Proc. 9 thth ECSMGE, ECSMGE, Dublin, vol.4.1, pp.355-357. Dublin, vol.4.1, pp.355-357.

Germanov,TGermanov,T. (1986). . (1986). Special problems in analyzing embankments).Special problems in analyzing embankments). Proc.8-th Danube-European Conference on SMFE, Proc.8-th Danube-European Conference on SMFE, Bericht zu Sitzung Bericht zu Sitzung EE,, Nurnberg, volNurnberg, vol.II, pp 65-67..II, pp 65-67.

Germanov, TGermanov, T.(1988). .(1988). Creep and ageing effects on stresses and Creep and ageing effects on stresses and deformations of saturated clayey soils”.deformations of saturated clayey soils”. Proc.Proc. Int. conf. on rheology Int. conf. on rheology and soil mechanics, Coventry, pp 194-203.and soil mechanics, Coventry, pp 194-203.

Germanov, T. & V.KostovGermanov, T. & V.Kostov (1994). Determination of Tailings (1994). Determination of Tailings Properties for Seismic Response Analysis of a Tailings Dam. Proc., 1Properties for Seismic Response Analysis of a Tailings Dam. Proc., 1stst International Conference on Environmental Geotechnics, Edmonton, International Conference on Environmental Geotechnics, Edmonton, pp. 499- 504.pp. 499- 504.

ReferencesReferences Germanov, T.Germanov, T. (2000). Effect of the Pore Water Pressure on the Stress-(2000). Effect of the Pore Water Pressure on the Stress-

Strain behavior of Earth Dams. Strain behavior of Earth Dams. Proc. of the GEOTECH - Year 2000 Proc. of the GEOTECH - Year 2000 Development in Geotechnical Engineering, AIT, Bangkok, pp.429-438.Development in Geotechnical Engineering, AIT, Bangkok, pp.429-438.

Isihara, K.Isihara, K. (1985). Stability of natural deposits during earthquakes; (1985). Stability of natural deposits during earthquakes; Proc. 11Proc. 11thth International Conf. On SMFE, San Francisco, Vol 2, pp.321- International Conf. On SMFE, San Francisco, Vol 2, pp.321-376.376.

Jessberger, H.L. & R. Kockel (1995). Jessberger, H.L. & R. Kockel (1995). Determination and assessment of Determination and assessment of the mechanical properties of waste. Proc. the mechanical properties of waste. Proc. Symposium Green Symposium Green 93,.Balkema, pp.313 – 322.93,.Balkema, pp.313 – 322.

Kaltchev IKaltchev I.(2003). Investigation and testing of pore pressure, phreatic .(2003). Investigation and testing of pore pressure, phreatic surface location and hydrodynamic surface location and hydrodynamic pressure in “Asarel – Medet” pressure in “Asarel – Medet” tailings dam. Proc. 13tailings dam. Proc. 13thth ECSMGE, Prague. ECSMGE, Prague.

Martin P., H.B.Seed (1978. Apollo, a computer program for the analysis Martin P., H.B.Seed (1978. Apollo, a computer program for the analysis of pressure generationof pressure generation and dissipation on horizontal sand layers during and dissipation on horizontal sand layers during cyclic or earthquake loading.. UCB/EEC-78/21cyclic or earthquake loading.. UCB/EEC-78/21

Vanicek, I.Vanicek, I. (1998). Talings dams for flying ash – some (1998). Talings dams for flying ash – some experiences experiences gained in CR. Proc. 3gained in CR. Proc. 3thth International Conference on environmental International Conference on environmental geotechnics, Lisbon. geotechnics, Lisbon.

Situation of the projectsSituation of the projects

““Liuliakovitsa”Liuliakovitsa”tailings damtailings dam

Blue LagoonBlue Lagoon

OxidativeOxidativepondpond

View of the slime pond “Blue Lagoon” View of the slime pond “Blue Lagoon” before encapsulationbefore encapsulation

Overview of all oxidative ponds near BurgasOverview of all oxidative ponds near Burgas

A borehole net consisting of 40 drillings, was elaborated A borehole net consisting of 40 drillings, was elaborated for for sampling from tailings damsampling from tailings dam. By using a standard . By using a standard drive sampling method, more than 50 undisturbed drive sampling method, more than 50 undisturbed samples were taken at different depths through 5 m. A samples were taken at different depths through 5 m. A representative sample is shown below.representative sample is shown below.

Sampling of Tailings MaterialsSampling of Tailings Materials

Oedometric tests apparatusOedometric tests apparatus

Oedometric tests - “Blue Lagoon”Oedometric tests - “Blue Lagoon”

Oedometric tests - “Oxidative pond”Oedometric tests - “Oxidative pond”