stabilisation as an alternative for mass exchange …
TRANSCRIPT
WASCON 2012 – GOTHENBURG, 30 MAY-1 JUNE 2012
STABILISATION AS AN ALTERNATIVE FOR MASS EXCHANGE FOR CLAYS WITH HIGH SULPHIDE CONTENT
M. Sc. Noora Lindroos, [email protected]
CONTENT
• Background
• Materials and methods
• Results from technical tests
• Results from environmental tests
• Conclusions
BACKGROUND OF SULPHIDE CLAYS
• Sulphide rich clay and silt
sediment occur in coast line of
Finland (100 000- 300 000 ha)
• The sediments date from the
Lithorina Sea period about 8000-
4000 years ago
• In the anoxic conditions of the
seabed bacterial activity resulted
in sulphate reduction to sulphide
and thus clay with high sulphide
content was formed.
Ref. GTK, Happamien sulfaattimaiden haitat hallintaan
BACKGROUND OF SULPHIDE CLAYS
• As a result of the uplifting process after glaciation period, the
former seabed has risen close to the surface
• Close to surface and above ground water level, sulphide oxidize to
sulphate and form sulphuric acid
• Acid generation result in the origin of acidic sulphate soils (pH of
2.5 to 4)
• Low pH values affect agriculture and forestry
• The release of significant amounts of aluminium and other
harmful heavy metals into river waters results in fish mortality
• Acidic water causes also corrosion in infrastructure
CHALLENGES OF CONSTRUCTION OF VAASA BY-PASS ROAD
• The road is planned to cross large area of sulphide/sulphate clays
• The construction of the road is possible either by extensive mass exchange of low
stability clays or by stabilisation of clays
• Excavation of sulphide clays from anaerobic environment and moving them to
aerobic conditions is not recommended without treatment, e. g. stabilisation
• This study demonstrates that by stabilisation the bearing capacity of
sulphide/sulphate clays can be improved and large mass exchange of about 400
000 m3 of sulphide/sulphate clays can be avoided
PRINCIPLE OF STABILISATION
Mass stabilisation equipment of Allu
MATERIALS - SOIL SAMPLING
Lighter coloured
oxidised acid
sulphate soil,
pH < 4,5
Black sulphide soil
layer below ground
water level in
anaerobic
conditions =
potential acid
sulphate soil pH
>6
Figure. A pit profile from excavation point
PROPERTIES OF SOIL SAMPLES
BINDERS USED IN STABILISATION TESTS
Abbreviation Name Features
Yse Portland composite cement
CEM II/A-M(S-LL) 42.5 N
SR Sulphate resistant Portland cement
CEM I 42.5 N
KJ400 Blast furnace slag
CaO Quick lime
GTC Mixture of gypsum, slaked lime and cement
LT1 Fly ash Coal burning
LT2 Fly ash of mixed fuel Peat, wood, REF burning
METHODS
• 1-axial unconfined
compression strength (UCS)
test
• For stabilised soil samples
• pH measurements
• For soil samples and stabilised soil samples
• Single step batch leaching test
(EN 12457-2)
• For soil samples and stabilised soil samples
TECHNICAL RESULTS FROM STABILISATION TESTS, COMPARISON OF BINDERS
• The most promising binders
are GTC and the mixtures of
GTC with fly ashes
• Fly ashes can serve as a
replacement of commercial
binders
• Bioash (LT2) is working better
with cement than coal ash
(LT1)
• The two fly ashes are equally
good when combined with GTC
0
50100150200250300350400450
1-a
xial
co
mp
ress
ion
str
en
gth
[kP
a]
Amount of binder [kg/m3]
K93 1,5-2,0 m
28 d 60 d
0
100
200
300
400
500
600
1-a
xial
co
mp
ress
ion
str
en
gth
[kP
a]
Amount of binder [kg/m3]
K93 1,5-2,0 m
28 d 60 d
TECHNICAL RESULTS FROM STABILISATION TESTS, EFFECT OF SAMPLING DEPTH
• UCS results for samples from
different depths vary widely
• UCS results are higher for
samples from deeper depth
than for surface samples
• Stabilisation results are poorer
in the acidic soil layers than in
the layers where the pH is
neutral or slightly alkaline
0123456789
0
50
100
150
200
250
300
1-a
xial
co
mp
ress
ion
str
en
gth
/ k
Pa
Stabilisation of samples from different depths, GTC+LT2= 75+ 100 kg/m3
28 d
pH of soil sample
pH
RESULTS FROM ENVIRONMENTAL TESTS
• For oxidised surface sample the pH remained constant (pH 4)
• Soil samples taken from black sulphide zone (<1 m depth) a clear
decrease in pH is observed (from pH 7..8 to pH 2,5...3,5)
• For stabilised samples the pH decline is smaller and pH seems to
settle down to pH 7,5...8,5
2
3
4
5
6
7
8
9
10
112
9.3
.20
11
12
.4.2
01
1
26
.4.2
01
1
10
.5.2
01
1
24
.5.2
01
1
7.6
.20
11
21
.6.2
01
1
5.7
.20
11
19
.7.2
01
1
2.8
.20
11
16
.8.2
01
1
30
.8.2
01
1
13
.9.2
01
1
pH
pH measurements
K93+K96/0,5-1,0m
K93/1,5-2,0m
K93/3,5-4,0m
K93/3,5-4,0m +LT2 300 kg/m3
K93/3,5-4,0m + GTC 100 kg/m3
K93/3,5-4,0m +75 kg/m3 GTC + 150 kg/m3 LT2
RESULTS FROM ENVIRONMENTAL TESTS, LEACHING TESTS
• All the results were below the
limit values set for a category
B1b landfill for regular
inorganic waste
Samples Landfill criteria for waste
K93 0,5- 4,0 m
300 kg/m3 LT2
100 kg/m3 GTC
75 kg/m3
GTC +150 kg/m3 LT2
A B1b
mg/kg mg/kg mg/kg mg/kg mg/kg mg/kg
Sb <0,02 0, 46 <0,02 <0,02 0,06 0,7
As 0,05 0,15 0,12 0,1 0,5 2
Ba 0,3 2,4 0,6 1,1 20 100
Cd <0,02 <0,02 <0,02 <0,02 0,04 1
Cr <0,02 2,1 <0,02 0,2 0,5 10
Cu <0,02 0,49 0,63 3,4 2 50
Pb <0,02 <0,02 <0,02 <0,02 0,5 10
Mo 0,1 1,8 0,6 1,1 0,5 10
Ni <0,02 <0,02 1,1 1,2 0,4 10
Se <0,02 0,11 <0,02 0,05 0,1 0,5
Zn <0,02 <0,02 <0,02 0,04 4 50
V <0,02 0,42 0,65 0,77
Al 0,5 1,9 0,1 0,5
Co <0,02 0,04 0,47 0,36
Mn 3,3 0,03 <0,02 <0,02
Fe 16 0,1 0,1 0,1
Cl- 2000 1900 1800 1800 800 15000
SO42- 3100 13000 11000 12000 1000 20000
The Amendment of Government Decision on Landfills 202/2006 in Finland / A = inert waste landfill category A, B1b = regular inorganic waste landfill category B1b
CONCLUSIONS
• Binder recipes can be developed for sulphide/sulphate clays
• Stabilisation can be carried out by mass stabilisation or
combination of mass stabilisation and column stabilisation
• The amount of GTC can be considerably diminished by utilisation
of fly ash in binder mixture
• The fly ash alone allows for the regulation of pH level of the acidic
clays, but compression strength may not be sufficient for earth
construction purposes
• By using mass stabilisation the construction of Vaasa by-pass
road can be done without extensive mass exchange
THANK YOU!