Closure Design and Construction of Contaminated Soft ... · Average shoe size: 10 (~ 0.75 ft2) 240...
Transcript of Closure Design and Construction of Contaminated Soft ... · Average shoe size: 10 (~ 0.75 ft2) 240...
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Closure Design and Construction of
Contaminated Soft Sludge Lagoons:
A Tale of Innovation, Poor Field
Execution and Final Redemption
David Espinoza
Washington DC, USA
April, 2013 West Lafayette, Indiana
PURDUE GEOTECHNICAL SOCIETY
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AVTEX SUPERFUND SITE
Located in the Shenandoah valley
(62 miles west of DC)
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A LITTLE HISTORY…
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ONCE UPON A TIME…
Plant built
in 1937
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AVTEX FIBERS
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SUPERFUND RECIPE
Ingredients:
• Caustic soda
• Sulfuric acid
• Carbon disulfide
1950s
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PRODUCE SOME MORE…
1970s
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ET VOILÀ (1990’s)…
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Sludge Basins
( 21 Hectares)
Fly Ash Stockpile
(500,000m3)
PROJECT BACKGROUND
Fly ash was recommended to close the lagoon (260,000 m3)
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REMEDIATION
• Leave in place and cap 5 sulfate sludge basins (~50 acres)
• Capping implied: 4 ft – 10 ft surcharge
Natural Soil
0.5 - 1.5 ft
3 - 20 ft
Crust (200 - 400 psf)
Soft (10-100 psf)
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CHARACTERIZATION
• Perm 10-7 to 10-8 cm/s
• Unit Weight: 10 pcf to 50 pcf
• Moisture Content: 90% to 800%
• Shear Strength: 10 psf to 100 psf
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HOW SOFT IT IS 10-100 PSF?
An average person weighs 180 lb
Average shoe size: 10 (~ 0.75 ft2) 240 psf
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CLOSURE APPROACH
Soil-Geosynthetic Cover
Sulfate Sludge
Fly Ash
Surplus of fly ash available on site (240,000 m3)
1-7 m
0.5-2 m
1 m
Use fly ash as grading fill
Place soil-geomembrane cap on the top
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THE $1M QUESTION IS:
How to over build a 10 PSF soft sludge lagoon?
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ANSWER: BROMS (1987)
Stabilization of Very Soft Clay using Geofabric
Geotextiles and Geomembranes Vol. 5, pp 17-28
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A. Lagoon Filled with Soft Sludge
LAGOON TO BE STABILIZED
(SOFT SLUDGE)
LAGOON TO BE STABILIZED
(SOFT SLUDGE)
HOW DOES IT WORK?
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A. Lagoon Filled with Soft Sludge
GEOTEXTILE SEAM (TYP)
STABILIZING BERM (TYP)
B. Install Geotextile over Lagoon
and Place Stabilizing Berms
CONSTRUCTION SEQUENCE
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A. Lagoon Filled with Soft Sludge
B. Install Geotextile over Lagoon
and Place Stabilizing Berm
INTERMEDIATE BERM
PERPENDICULAR TO SEAMS (TYP)
C. Construct Intermediate Berms
CONSTRUCTION SEQUENCE
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A. Lagoon Filled with Soft Sludge B. Install Geotextile over Lagoon and
Place Stabilizing Berm
D. Widen Intermediate Berms C. Construct Intermediate Berms
CONSTRUCTION SEQUENCE
Construction involves a step-wise procedure to be followed in the field
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SOFT SLUDGE
STABILIZING BERM HIGH STRENGTH GEOTEXTILE
CLOSURE METHOD
SOFT SLUDGE
LOCKING BERM
SOFT SLUDGE
INTERMEDIATE BERM
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BROMS (1987)
2
2
1
1
l
h
l
h
Hypothesis:
12
12
5
5
hh
ll
For example:
Excerpts from Page 23:
ft5)ft1(5 ft;1
ft50)ft10(5 ;ft10
21
21
hh
ll
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NEW APPROACH (2000)!
CE68901
CE48300 MA161000
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DESIGN ANALYSIS
SOFT SLUDGE
INTERMEDIATE BERM
HIGH STRENGTH
GEOTEXTILE
LOCKING BERM STABILIZING BERM
Bearing Capacity Analysis
BERM SPACING INTERMEDIATE
BERM
DEFORMED
SURFACE
INITIAL
SURFACE
RUT DEPTH
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DESIGN ANALYSIS
Ab = Volume of soft sludge displaced under an intermediate berm
Ah = Volume occupied by soft Sludge heave between intermediate berms
BERM AREA Lb
HEAVED AREA Lh
BERM AREA Lb
INTERMEDIATE
BERM
Ab βh βb
Ah
Ab
rh
rb
εh
βb
rb
Ultimate Reinforced Bearing Capacity of Soil, qur
(Membrane Effect from High Strength Geotextile)
DEFORMED GROUND
SURFACE, f(x)
qur = cNc +qgb +qgh
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q + q + N c = q ghgbcur
dxxfxfx L
J = q
b
b
L
Lb
gb
2/
2/
2/12 )('')('1)(
dxxfxfx L
J = q
hb
b
LL
Lcgh
2/2/
2/
2/12 )('')('1)(2
qavg
Reference: Espinoza and Sabatini (2008), Geosynthetics International
Data required: Modulus (J) and shape of deformation f(x)
DESIGN ANALYSIS
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b
h
L
L
+ + = 2J/L
qhhbbavg
b
avg
q
)secln(tan
1)sec(tanln
)(
1
ghgb
avg
Deformed shape approximated by parabolas (Giroud and Noirey, 1981)
ghgbavg qqq
DESIGN ANALYSIS
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GEOTEXTILE CONTRIBUTION
Using this chart, the effect of geotextile contribution can be quantified
Additional Bearing Capacity Provided by Reinforcement
0.000
0.100
0.200
0.300
0.400
0.000 0.050 0.100 0.150 0.200 0.250 0.300
Rutting Factor - rb/Lb
Mem
bra
ne C
on
trib
uti
on
- q
/(2J/L
b)
0.0%
5.0%
10.0%
15.0%
20.0%
Avera
ge R
ein
forc
em
en
t S
train
(%
)
1.00
1.50
2.00
3.00
4.00
5.00
L h /L bReinforcement Strain
Membrane Effect Contribution
Rutting Factor (rb/Lb)
Mem
bra
ne
Co
ntr
ibu
tio
n
λ=
qu
r/(2
J/L
b)
Ave
rag
e
Str
ain
(%
)
Additional Bearing Capacity Provided by Reinforcement
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Sludge Thickness = 0.3m
Undrained shear strength= 0.5 kPa
Equipment CAT D3C-LGP-5II = 29.6 kPa
kPaN c = q cu 5.214.55.0
0.108.06.29
5.2 =
q
qFS
equipment
u
For Berm Deflection rb= 0.45m
Berm spacing Lh= 8.0 m
Berm width Lb= 2.7 m
17.0,0.3 b
b
b
h
L
r
L
L
CALCULATION
Unreinforced Case
Reinforced Case with Berms
Lh=8.0m INTERMEDIATE
BERM
DEFORMED
SURFACE
INITIAL
SURFACE
rb=0.45m
Lb=2.7m
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GEOTEXTILE CONTRIBUTION
Additional Bearing Capacity Provided by Reinforcement
0.000
0.100
0.200
0.300
0.400
0.000 0.050 0.100 0.150 0.200 0.250 0.300
Rutting Factor - rb/Lb
Mem
bra
ne C
on
trib
uti
on
- q
/(2J/L
b)
0.0%
5.0%
10.0%
15.0%
20.0%
Avera
ge R
ein
forc
em
en
t S
train
(%
)
1.00
1.50
2.00
3.00
4.00
5.00
L h /L bReinforcement Strain
Membrane Effect Contribution
Rutting Factor (rb/Lb)
Mem
bra
ne
Co
ntr
ibu
tio
n
λ=
qr/(2
J/L
b)
Ave
rag
e
Str
ain
(%
)
Calculating factors using the proposed chart
rb/Lb=0.17
λ=0.014
ε=1.9%
Lh/Lb=3.0
With = 1.9% and qr = 27.1 kN/m then J= 2540 kN/m
Geosynthetic Contribution
Working tensile strength = (2,540 kN/m)×1.9% = 48.25 kN/m
For FS =2, u = 3.8%, Tu = 96.5 kN/m
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SPECIFICATIONS
• Develop construction details
• Specifications
• High strength geotextile (Tu = 96.5 kN/m and u = 3.8%)
• Sequence of construction
• Equipment (D5G-LGP)
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CLOSURE IMPLEMENTATION
Fill Placement to slow and
time consuming
Specified Equipment (e.g.,
D5H-LGP) too small for
production
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Interesting but no, thanks
Use large equipment to push fly ash over sludge to
“save” the cost of geotextile and construction time
(2002-2008)
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After all it is just a dirt job…
Mixing lots
of fill with
sludge
Crust
Displacement
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9 Years later (2009)…
Closed 12 hectares
Fly Ash Stockpile
(500,000m3)
Slow rate of closure and fly ash deficit for remaining work
Remaining 9 hectares
Used 400,000 m3 Remaining 100,000 m3
Sludge Basins
(21 hectares)
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FINAL REDEMPTION
Maybe the
consultant is not as
dumb as he looks
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Field panels seamed in accordion manner in the field
SEAMS FOR GEOTEXTILES
J SEAM HAND SEAMING
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Minimal slack following deployment of the seamed geotextiles
FIELD CONSTRUCTION
Geotextile installed rapidly in the field
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Ease of placement of fly ash material over sludge using equipment on site
Fly ash layer placement perpendicular to geotextile seams
FIELD CONSTRUCTION
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Increased bearing capacity due to membrane effect of geotextile
Parallel berms provided confinement to the sludge
FIELD CONSTRUCTION
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Wave Propagation at Leading Edge of Berms Occurred
Approximately 2 Weeks to Cover 2 Acre Area with Initial Lift
of Fly Ash Grading Layer
FIELD CONSTRUCTION
Reduced construction time to one month to cover one hectare of basin
Series of parallel berms were constructed
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Geotextile was torn and patched in place
Problems occurred when the contractor tried to use oversized equipment
FIELD CONSTRUCTION
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FIELD CONSTRUCTION
Fill thickness of 1-3 m was achieved with remaining fly ash
Intermediate space between berms was filled
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LESSONS LEARNED
Printed correct
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LESSONS LEARNED
• Developing good engineering solutions is not always sufficient
• Convey the risks associated with potential alternatives
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TO BE A GOOD CONSULTANT…
We CANNOT focus in our mouse traps…
Remember, our clients don’t care about our
mouse traps…
They care about
having less mice
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THANKS
Questions?
Contact Information: David Espinoza [email protected]
Address: 10220 Old Columbia Road, Columbia, MD 21046
(Ph: 410-381-4333)