field experimental observations

heehawultraMécanique

22 févr. 2014 (il y a 3 années et 1 mois)

46 vue(s)

W.L.
Oliveira‐Filho, UFOP

D.R.
Silva, SAMARCO

F.E.
Almeida, SAMARCO

Thickening of iron ore tailings
slimes using sub
-
aerial deposition:
field
experimental
observations


Introduction


Background


Field experimental studies


Analyses of experimental data


C
onclusion


Contents

Introduction

Desiccation

&
Sub
-
aerial

Studies

Timeline

Background

Alternative

d
isposal

techniques

for
slimes


Types


sub
-
aerial

deposition


Thickened


Paste


filtered


Common
aspects


Intermitent
:
cycles

of

waiting

and

disposal

periods


Physical

processes:
sedimentation
,
consolidation

and

desiccation




Background

Desiccation


Importance


The
most effective
phenomena for rehabilitation work, optimizing storage,
and reducing
risks regarding containment structure
failure


Triggering

mechanisms


Surface

drying


Lowering

the

GWT


Driving

force
and

Phases


Suction


1D
shrinkage


3D
shrinkage

(
cracking
)


Comprehensive

works


Abu
-
Hejleh

&
Znidarcic

(1995) and
Yao
et al.

(2002
)


Konrad

&
Ayad

(1997)


Fujiyasu

(1997)


Background


Constitutive

relations

Compressibility

Permeability


Cracking

function


a

-

晵湣ni潮

Main
input
relationships for
analyses with
CONDES (Yao et al. 2002)

Field experimental
studies

Goal

&
strategies


T
o
gain some understanding of the main mechanisms that play a
role in the sub
-
aerial method applied to
Samarco’s

slimes


T
o
investigate consolidation separately from
desiccation using a
field
experiment


To focus on slimes desiccation because was
lesser known and more
challenging


Field experimental
studies

Site &
operations


Location: inside
the
Germano

tailings impoundment
(
Samarco

Mineração

S.A
.)
in
Mariana,
MG.


Impoundment figures: 3

m high ring dyke, confining an area of 4,850

m
2
.


Foundation: 2

m of coarse siliceous tailings, grading from fine sand to medium silt,
underlain by a deep layer of iron tailings slimes.


Ground
water
table: at
the contact of those layers, 2

m below the surface.


Drainage system: stop
logs

installed at the lower
part (bottom at 2% slope)


Access: a
pier to the centre of the testing area
for
instrumentation maintenance
and sampling
operations


Filling: slimes
pumped from an adjacent slimes pond at the
Germano

impoundment


Water

cover:
5 to 10

cm deep during
the filling
process and consolidation period to
prevent early
desiccation.


Surface

w
ater

removal
:

for
the desiccation part of the test.


Field experimental
studies

Instrumentation,
testing

&
instalation


Devices:


Geotechnical: Thermistors
, settlement devices (staff gauges), tensiometers,
piezometers,
time
domain reflectometry probes (TDRs
)


Climate: Weather
station and a class A pan
test


Placement:


Thermistors and TDR probes launched at certain pond elevations during the deposit
filling (movable position)


All other instruments at fixed positions


Testing


Periodic
sampling using a stationary
sampler


Gravimetric
water content
determination


Specific
gravity and bulk
density.

Field experimental
studies

Overview
of the testing site

Analyses

of

experimental data

Analyses

Data/
Parameters





Consolidation





Compressibility and Permeability parameters

A (kPa
-
1
)

2.5438

B

-
0.1920

C (m/dia)

9.45 x 10
-
4

D

4.2370

Z (kPa)

0.0495

Boundary conditions

Bottom

h
p
= variable

Top

Surcharge null

Specific gravity
-

G

3.89

Filling rate (m/day)

0.0603

Filling period (day)

34





Desiccation







Cracking function parameters

A

0.3859

B

0.0508

C

1.3665

D

0.626 x 10
18



Boundary conditions

Bottom

h
p
=
-
0.55 m

Top

Evap. rate =

0.002
m/day

Input data
for analyses with CONDES

Analyses

of

experimental data

Progress
of the deposit height
(at day 84 starts desiccation)

Analyses

of

experimental data

Progress
of volumetric water content
(day 84 starts desiccation)

Analyses

of

experimental data

Progress
of gravimetric water content
(desiccation starts at day 84)

Analyses

of

experimental
data

Progress
of bulk densities
(desiccation starts at day 84)

Analyses

of

experimental data

Progress
in solids content
(desiccation starts at day 84)

Analyses

of

experimental data

Progress of
porepressure

at base
(
desiccation starts at day 84)

Analyses

of

experimental data

Meteorological
data during field experiments
(desiccation starts at day 84)

Analyses

of

experimental data

Progress
of evaporation with data from the weather station and Class A device

Analyses

of

experimental data

Progress
of cracking (a) day 89, (b) day 92, (c) day
94

Conclusions


Characterization of
the desiccation behaviour of a fine tailings from the
iron ore milling
operations was successfully reached.


A
test
section was built and monitored,
using an extensive sort of
instruments and
tests.


Material
behaviour and boundary conditions
were assessed such
as
settlement, water content, bulk densities, solids content,
porewater

pressures, evaporation rates, etc.


Cracking
morphology has also been described.


Sub
-
aerial deposition conditions was examined as a part a large study of
alternative methods for slimes.


A
brief comparison of field data with a numerical modelling of the
problem
was presented
and the results have shown consistent agreement
.


Overall
, the research seems to suggest that reasonable efficiency with
slimes thickening
can be achieved by the sub
-
aerial disposition method.


THANK YOU