attachment d9 - the fundÃo tailings dam...

Fundão Tailings Dam Review Panel

Report on the Immediate Causes of the Failure of the Fundão Dam Appendix D – Laboratory Geotechnical Data and Interpretation

August 25, 2016

ATTACHMENT D9 University of Alberta Sedimentation/Consolidation Test on Slimes

1

Large Strain Consolidation Testing of

Flotation Tailings

Prepared for

Klohn Crippen Berger

Prepared by

Louis K. Kabwe, Ph.D.

Research Associate

and

Ward G. Wilson, Ph.D., P.Eng., P.Geol., FCAE

Principle Investigator

June 2016

2

Table of Contents

Table of Contents…………………………………………………………………………… 2

List of Tables (Main body)………………………………………………………………… 3

List of Figures (Main body)…………………………………………………………. 3

List of Figures in Appendix A……………………………………………………… 3

List of Tables in Appendix B………………………………………………………. 3

List of Figures in Appendix C………………………………………………………. 3

1. Introduction………………………………………………………………………… 4

2 Tailings Sample……………………………………………………………………. 4

3. Large Strain Consolidation Test…………………………………………………. 4

3.1 Large Strain Consolidation Apparatus ……………………………………………… 5

3.2 Determination of End of Consolidation ……...……………………………………... 5

3.3 Hydraulic Conductivity Test………………………………………………………… 7

3.4 Shear Strength Test………………………………………………………………….. 8

4. Summary of Results……………………………………………………………….. 9

5. Observations ………………………………………………………………………. 12

APPENDICES

Appendix A Large Strain Consolidation Test Setup.…………………………………. 13

Appendix B Sample Water Chemistry……………………………………………….. 15

Appendix C Time – Settlement and Pore Pressure Dissipation Plots………………… 18

List of Tables (main body)

Table 1: Measured Large Strain Consolidation Properties of Tailings Sample…..... 9

Table 2: Tailings Sample Properties………………………………………………… 10

3

List of Figures (main body)

Figure 1: Large strain consolidation set up…………………………………………... 5

Figure 2: Typical large strain consolidation time-settlement curve ……………….... 6

Figure 3: Typical excess pore pressure dissipation curve.…………………………... 6

Figure 4: Set up of hydraulic conductivity measurement……………………………. 7

Figure 5: Compressibility plot (void ratio versus effective stress)............................... 11

Figure 6: Permeability plot (hydraulic conductivity versus void ratio)…………….... 11

List of Figures in Appendix A

Figure A1 Schematic set up of the large strain consolidation test, step 1…………….. 14



List of Tables in Appendix B

Table B1 Anions concentrations in tailings water sample…………………………… 16

Table B2. Cations concentrations in tailings Water sample…………………………. 16

Table B3. Other water chemistry in tailings water sample…………………………… 17

List of Figures in Appendix C

Time – settlement and excess pore pressure dissipation plots…………………………… 19

4

1. INTRODUCTION

Klohn Crippen Berge contracted the University of Alberta Geotechnical Centre to perform

Large Strain Consolidation (LSC) testing services for Flotation Tailings.

This report consists of two main parts: the main body and the appendices. Detailed data are

presented in tables and figures in appendices. The tables and figures in the main body of the

report summarize the results of the tests, and are briefly discussed. The appendix tables and

figures will not be discussed and are presented so the report includes all data from the testing

program. Large files of measurement data are not included in this report but will be transmitted

to Klohn electronically.

2. TAILINGS SAMPLE

A 15 L container of tailings sample was received from Klohn Crippen Berge for LSC testing

program. The solids content of the sample was measured upon arrival and was found to be

over 76 %. The specific gravity of the sample (3.85) was not measured in this test but was

provided by Klohn. The solids content of the sample was reduced to about 50% by mixing the

sample with distilled water. The decanted water after mixing was used for hydraulic

conductivity measurement at the end of consolidation for each load step. The water chemistry

of the tailings sample was measured and results are presented in Appendix B.

3. LARGE STRAIN CONSOLIDATION TEST

The objectives of the LSC tests are:

• To determine the relationship between effective stress and void ratio.

• To determine the relationship between void ratio and hydraulic conductivity

(permeability of water).

5

3.1 Large Strain Consolidation LSC Apparatus

A LSC test was performed in a standard consolidation apparatus (150 mm dia. x 150 mm high).

The LSC apparatus used in this testing program confines the slurried material so it can be tested

at any water content. The first applied stress, the self-weight of the slurry, can be about 0.3 to 0.5

kPa. Effective stresses up to about 10 kPa were applied by dead loads acting on the piston

(Figure A1 in Appendix A). Effective stresses over 10 kPa were applied in a loading fram by an

air pressure Bellofram. Subsequent loads were approximately doubled for each load step up to

1000 kPa maximum. The setup of the LSC test used at the geotechnical centre of the University

of Alberta is shown in Figures 1 and Figure A1 in Appendix A.

Figure 1. Set up of the large strain consolidation LSC test at the Geotechnical Centre of the

University of Alberta.

3.2 Determination of End of Consolidation

When a load is applied, the progress of the consolidation is evaluated by monitoring the change

in height of the sample (vertical strain) with a LVDT and by measuring the pore pressure at the

6

base of the sample. The load is maintained until the vertical strain/or base pore pressure

dissipation are significantly completed before adding the next load as shown in Figures 1 and 2.

Figure 2. Typical time-settlement curve in LSC test.

Figure 3. Typical excess pore pressure dissipation curve in LSC test.

6.05

6.10

6.15

6.20

6.25

6.30

6.35

6.40

6.45

6.50

0 50 100 150 200 250 300 350

100 kPa

LV

D (

cm)

Time (min)

Time - Settlement Curve

0

10

20

30

40

50

60

0 50 100 150 200 250 300 350

400 kPa

Ex

cess

pore

pre

ssure

(kP

a)

Time (min)

Excess Pore Pressure Dissipation

7

3.3 Hydraulic Conductivity (Permeability) Test

The permeability was measured at the end of consolidation for each load step. An upward flow

constant head test was performed with the head difference h (h=ho-h1) being kept small enough

so that seepage forces will not exceed the applied stress and cause sample fracturing during the

permeability test.

In one dimension, water flows through a fully saturated soil sample in accordance with Darcy’s

empirical law is given by:

ikAq =

or

kiA

qv ==

Where q = volume of water flowing per unit time, A = cross-sectional area of soil sample

corresponding to the flow q, k = coefficient of permeability, i = hydraulic gradient, and v =

discharge velocity. The hydraulic gradient, i, is given by:

Figure 4. Setup of permeability measurement.

l

hh

l

hi o 1

−==

Where

l = the length of the sample.

The inflow is monitored to ensure that steady state flow conditions are obtained. The units of the

8

coefficient of permeability are those of velocity (m/s).

For a given soil, the coefficient of permeability is a function of void ratio. The coefficient of

permeability depends primarily on the average size of the pores, which in turn is related to the

distribution of particles sizes, particle shape and soil structure. The presence of a small

percentage of fines in a coarse-grained soil results in a value of k significantly lower than the

value for the same soil without fines.

3.4 Van Shear Test

The laboratory vane shear test consists of inserting a four-bladed vane in the end of a tube

sample and rotating it at a constant rate to determine the torque required to cause a cylindrical

surface to be sheared by the vane. This torque is then converted to unit shearing resistance of the

cylindrical surface area. The torque is measured by a calibrated torque transducer that is attached

directly to the vane. The undrained shear strength is calculated using the following expression:

T = τ x K

Where:

T = torque, lbf.ft (N.m)

τ = undrained shear strength, lbf/ft2 (Pa), and

K = vane blade constant, ft3 (m3).

T and K are given as follows (assuming the distribution of the shear strength is uniform

across the ends of the failure cylinder and around the perimeter):

+=

=

+=

3

1

2

3

1

2

3

3

v

v

y

y

v

v

D

HDK

K

T

D

HDT

π

τ

τπ

Where:

Dv = measured diameter of the vane, in. (mm),

H = measured height of the vane, in. (mm).

9

4. SUMMARY OF RESULTS

The LSC tests results are summarized in Tables 1 and 2 and in Figures 4 and 5.

Table 1. Summary of measured large strain consolidation properties of tailings sample.

Load Effective

stress

Sample

height

Void

ratio

Hydraulic

conductivity

Solids

content

(kPa) (cm) (m/s) (%)

Self-

weight

settling 0.4 7.0 2.61 7.84E-08 50.0

Load-1 1.1 6.5 2.34 6.67E-08 60.4

Load-2 2.0

6.0 2.08 3.88E-08 63.3

Load-3 2.9

5.8 1.93 3.13E-08 64.9

Load-4 3.8

5.6 1.85 2.87E-08 65.9

Load-5 8.4

5.3 1.67 1.83E-08 68.2

Load-6 13.0

5.0 1.53 1.33E-08 70.0

Load-7 30

4.6 1.27 6.97E-09 73.8

Load-8 100

4.2 1.08 3.66E-09 76.9

Load-9 200

4.1 1.02 2.43E-09 77.9

Load-10 400

3.9 0.94 2.22E-09 79.1

Load-11 600

3.8 0.89 1.83E-09 80.0

Load-12 1000

3.7 0.83 1.21E-09 81.1

10

Table 2. Summary of tailings sample properties.

Tailings sample

(Gs = 3.85)

Initial

(prior to

consolidation)

Final

(after 1000 kPa

effective stress)

Solids content

(oven-dry) (%)

50

82

Void ratio

(oven-dry) 2.61

0.85

Shear strength (kPa)

144

11

Figure 4. Compressibility plot (void ratio vs effective stress) of the tailings sample.

Figure 5. Permeability plot (hydraulic conductivity vs void ratio) of the tailings sample.

0.2

0.6

1.0

1.4

1.8

2.2

2.6

3.0

0 1 10 100 1,000 10,000

Data

Effective stress (kPa)

Void

rat

ioCompressibility Plot

y = 3E-09x3.7106

R² = 0.9965

1.0E-10

1.0E-09

1.0E-08

1.0E-07

1.0E-06

0.0 0.5 1.0 1.5 2.0 2.5 3.0

data

Hydra

uli

c co

nduct

ivit

y (

m/s

)

Void ratio

Permeability Plot

12

5. OBSERVATIONS

Figure 4 shows that the compressibility (the relationship between void ratio e and effective stress

σ’) increases linearly when effective stresses are between 2 and 30 kPa. The compression index

Cc (i.e., the slope of the linear portion of the e-logσ’ curve) is about 0.026.

Figure 5 shows the relationship between hydraulic conductivity k and void ratio e. The k

decreases exponentially as e decreases. The k decreases by one order of magnitude (i.e., from

7.84x10-8 m/s to 6.97x10-9 m/s) when e decreases from 2.6 to 1.27. By fitting a mathematical

equation to the data points, it is found that a power law yields the prediction equation with high

correlation coefficient (R2=0.996) for the tailings sample tested.

13

APPENDIX A

Large Strain Consolidation Set Up at the

University of Alberta Geotechnical Centre

14

Figure A1. Initial set up of the large strain consolidation test before loading sample

Figure A2. Sample loaded with piston and dead loads up to about 10 kPa

Figure A3. Sample in loading frame and loaded by Bellofram up to 1000 kPa.

15

APPENDIX B

Tailings Sample Water chemistry

16

Table B1: Anions concentrations in tailings water sample.

mg/L mmol/L mEq/L

fluoride 0.34 1.790E-02 1.790E-02

chloride 5.13 1.447E-01 1.447E-01

nitrite 0.72 1.565E-02 1.565E-02

bromide 0 0 0

sulphate 36.0505 3.753E-01 7.506E-01

nitrate 14.675 2.367E-01 2.367E-01

phosphate 0 0 0

bicarbonate 2.092E+01 3.428E-01 3.428E-01

carbonate 2.417E-03 4.027E-05 8.054E-05

Table B2: Cations concentrations in tailings water sample.

mg/L mmol/L mEq/L

Na23 30.61064 1.331 1.33089739

Mg26 0.0448 1.723E-03 3.446E-03

Si28 1.52866 5.460E-02 2.184E-01

K39 1.96852 5.047E-02 5.047E-02

Ca43 16.67744 3.878E-01 7.507E-01

Ca44 15.9656 3.629E-01

Cr52 0.0072 1.385E-04 4.154E-04

Ni58 0.00302 5.207E-05 2.083E-04

Cu63 0.00206 3.270E-05 6.540E-05

Zn64 0.0152 2.375E-04 4.775E-04

Zn66 0.01584 2.400E-04

Sr86 0.15002 1.744E-03 3.019E-03

Sr88 0.1122 1.275E-03

Mo95 0.00756 7.958E-05 3.133E-04

Mo96 0.0074 7.708E-05

Ba138 0.00634 4.594E-05 9.188E-05

17

Table B3: Other tailings water chemistry (OH- & H+)

mmol/L mEq/L mEq/L

OH- 2.512E-05 2.512E-05 negative

-

1.508422783

H+ 3.981E-04 3.981E-04 positive 2.358889696

difference 0.850466913

18

APPENDIX C

Time – Settlement Plots and

Excess Pore Pressure Dissipation Plots for the

Large Strain Consolidation LSC Test

19

Figure C1. Time – settlement curve for 1.12 kPa effective stress.

Figure C2: Excess pore pressure dissipation for 1.12 kPa effective stress.

1.52.02.53.03.54.04.55.05.56.06.57.0

0 1000 2000 3000 4000 5000 6000

1.12 kPa

LV

DT

(m

m)

Time (min)


-0.05

0.00

0.05

0.10

0.15

0.20

0.25

0.30

0.35

0 1000 2000 3000 4000 5000 6000

1.12 kPa

Ex

cess

pore

pre

ssure

(kP

a)

Time (min)


20



-2.5-2.0-1.5-1.0-0.50.00.51.01.52.02.53.0

0 500 1000 1500 2000 2500 3000

2.02 kPa

LV

DT

(m

m)

Time (min)

Time Settlement Curve

0.00

0.05

0.10

0.15

0.20

0.25

0.30

0.35

0.40

0 500 1000 1500 2000 2500 3000

2.02 kPa

Pore

pre

ssure

(kP

a)

Time (min)


21



1.0

1.5

2.0

2.5

3.0

3.5

4.0

4.5

5.0

0 400 800 1200 1600 2000 2400

2.92 kPa

LvD

T (

mm

)

Time (min)


0.0

0.2

0.4

0.6

0.8

1.0

1.2

0 400 800 1200 1600 2000 2400

2,92 kPa

Pore

pre

ssure

(kP

a)

Time (min)


22



-1.5

-1.3

-1.1

-0.9

-0.7

-0.5

-0.3

-0.1

0.1

0.3

0 1000 2000 3000 4000 5000 6000

3.82 kPa

LV

DT

(m

m)

Time (min)


0.00

0.05

0.10

0.15

0.20

0.25

0.30

0 1000 2000 3000 4000 5000 6000

3.82 kPa

Ex

cess

pore

pre

ssure

(kP

a)

Time (min)


23


Figure C10: Excess pore pressure dissipation for 8.42kPa effective stress.

-1.0-0.6-0.20.20.61.01.41.82.22.63.0

0 500 1000 1500 2000 2500

8.42 kPa

Time (min)


LV

DT

(m

m)

-0.20.0

0.20.40.60.81.01.21.4

1.61.8

0 500 1000 1500 2000 2500

8.42 kPa

Ex

cess

pore

pre

ssure

(kP

a)

Time (min)


24

Figure C11. Time – settlement curve for 30 kPa effective stress.

Figure C12: Excess pore pressure dissipation for 30 kPa effective stress.

6.4

6.5

6.6

6.7

6.8

6.9

7

0 200 400 600 800 1000 1200 1400

30 kPa

LV

DT

(cm

)

Time (min)


-0.001

0

0.001

0.002

0.003

0.004

0.005

0.006

0 200 400 600 800 1000 1200 1400

30 kPa

Ex

cess

pore

pre

ssure

(kP

a)

Time (min)


25



6.05

6.10

6.15

6.20

6.25

6.30

6.35

6.40

6.45

6.50

0 50 100 150 200 250 300 350 400 450 500

100 kPa

LV

D (

cm)

Time (min)


0

5

10

15

20

25

30

35

0 50 100 150 200 250 300 350 400 450 500

100 kPa

Ex

cess

pore

pre

ssure

(kP

a)

Time (min)


26



7.88

7.90

7.92

7.94

7.96

7.98

8.00

8.02

8.04

0 200 400 600 800 1,000 1,200 1,400 1,600

200 kPa

LV

D (

mm

)

Time (min)


-0.010

0.000

0.010

0.020

0.030

0.040

0.050

0.060

0 200 400 600 800 1000 1200 1400 1600

200 kPa

Ex

cess

pore

pre

ssure

(kP

a)

Time (min)


27



7.767.787.807.827.847.867.887.907.927.947.96

0 250 500 750 1,000 1,250 1,500

400 kPa

LV

D (

cm)

Time (min)


0

10

20

30

40

50

60

0 250 500 750 1000 1250 1500

400 kPa

Ex

cess

pore

pre

ssure

(kP

a)

Time (min)

Excess pore pressure Dissipation

28



7.14

7.16

7.18

7.20

7.22

7.24

7.26

0 250 500 750 1,000

600 kPa

LV

D (

mm

)

Time (min)


0

5

10

15

20

25

30

0 200 400 600 800 1000

600 kPa

Ex

cess

pore

pre

ssure

(kP

a)

Time (min)


29



7.97

7.98

7.99

8.00

8.01

8.02

8.03

8.04

8.05

0 100 200 300 400 500

1000 kPa

LV

DT

(cm

)

Time (min)

Time - Settlement curve

-2

0

2

4

6

8

10

12

14

0 50 100 150 200 250 300 350 400 450 500

1000 kPa

Ex

cess

pore

pre

ssure

(kP

a)

Time (min)


1

Summary of Settlement Test

1. Settlement Test Setup

The settlement test was conducted in the same cell used for the consolidation tests (150 mm

dia. x 150 mm high) (Figures 4 and 5). The sample slurry of 48% solids content was prepared

from the original sample (as received) by dilution with distilled water. The void ratio of 4.17

was calculated using the specific gravity of Gs = 3.85 provided by Klohn Crippen Berger. The

initial sample height was 7 cm (Figure 4) and final sample height after settling was 5.5 cm. The

change of sample height (interface) was measured at different time interval by visual

observation on a measuring tape placed on the consolidation cell. The total pore water

pressure was continuously monitored at the base of the sample using a transducer (Figure 4).

2. Summary of Settlement Test results

Figures 1 and 2 show the change of sample interface (sample height) and dissipation of excess

pore pressure measured with time. It is noted that Figure 2 shows immediate decrease in

excess pore pressure with settlement of the interface. As the excess pore pressure fully

dissipates the sample has also settled completely. Consolidation is defined as dissipation of

excess pore pressure, therefore this is a settling process not a sedimentation process.

Figure 1. Interface settlement measured with time during settlement.

5.2

5.4

5.6

5.8

6.0

6.2

6.4

6.6

6.8

7.0

7.2

0 5 10 15 20 25 30 35 40 45 50

Data1

Time (Hrs)

Sa

mp

le in

terf

ace

(cm

)

Self-weight settling

(Tailing: 48% solids content)

2

Figure 2. Excess pore pressure dissipation during settlement.

0.00

0.05

0.10

0.15

0.20

0.25

0.30

0 5 10 15 20 25 30 35 40 45 50

Data2

Exc

ess

po

re p

ress

ure

(kP

a)

Time (Hrs)

Self-weight settling

Tailings: 48% solids content)

3

Figure 3. Settlement test conducted in a consolidation cell at the beginning of the test.

Figure 4. Settlement test conducted in a consolidation cell at the end of the test.

Transducer for

pore pressure

measurement

Tailings slurried sample

attachment d9 - the fundÃo tailings dam...

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