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Center for Earthworks Engineering Research
A Comparison of Pavement Foundation Stabilization TechnologiesPeter J. Becker, M.S.
Graduate Research Assistant
Center for Earthworks Engineering Research (CEER)
pbecker@iastate.edu
David J. White, Ph.D., P.E.
Associate Professor and holder of Richard L. Handy Professorship
Director, Center for Earthworks Engineering Research (CEER)
Department of Civil, Construction and Environmental Engineering
Iowa State University
djwhite@iastate.edu
Center for Earthworks Engineering Research 2
This presentation will compare the performance of different pavement foundation stabilization techniques used at the Central Iowa Expo (CIE) roadway reconstruction• Project overview• Performance (as constructed, freeze-thaw, &
recovering)• Cost analysis
Center for Earthworks Engineering Research 3
The testing area encompasses 24 test sections distributed over 12 north-south roads
Center for Earthworks Engineering Research 4
Prior to reconstruction, each test section comprised the following cross section
GRANULAR BASEA-1-a (SM)
SUBGRADEA-6(5) (CL)
BIAXIAL GEOGRID
Existing Profile
CHIPSEALCOATING
8”
Center for Earthworks Engineering Research 5
Roadways were reconstructed with different pavement foundation stabilization techniques• Control• Mechanical stabilization of subgrade (Mix A-1-a with A-6(5))• Geocell-reinforced subbase (4 in. and 6 in.)• Geotextile fabric (non-woven and woven)• Polymer grid (biaxial and triaxial)• 5% cement stabilized subbase• 5% cement and 0.4% fiber stabilized subbase
• Fibrilated polypropylene (FP) and monofilament polypropylene (MP) fibers
• Recycled subbase• 10% cement (PC) stabilized subgrade• 10%, 15%, and 20% fly ash (FA) stabilized subgrade• High Energy Impact Compaction (Converted to control section)
Center for Earthworks Engineering Research 6
Performance was measured using the following in situ testing equipment
Falling Weight Deflectometer (FWD)Dynamic Cone Penetrometer (DCP)
Center for Earthworks Engineering Research 7
Mechanical stabilization of subgrade is the mixture of good quality geomaterial with poor quality subgrade
Particle Diameter (mm)
0.0010.010.1110100
Per
cent
fin
er (
%)
0
20
40
60
80
100
SubgradeReclaimed SubbaseMechanically Stabilized Subgrade (Average)Mechanically Stabilized Subgrade
Control Mech. Stab.
Ave
rage
Sub
base
Mod
ulus
, E
SB
-FW
D (
psi)
0
5000
10000
15000
20000July 2012 (shortly after stabilization)October 2012April 2013 (after spring-thaw)May 2013
Control Mech. Stab.
Ave
rage
Cal
iforn
ia b
earin
gra
tio in
sub
grad
e or
recy
cled
sub
base
, CB
RS
G/R
SB
1
10
100July 2012 (shortly after stabilization)October 2012April 2013 (after spring-thaw)May 2013
Center for Earthworks Engineering Research 8
Geocells use confinement to strengthen geomaterials
Control 4 in. Geocell 6 in. Geocell
Ave
rage
Sub
base
Mod
ulus
, E
SB
-FW
D (
psi)
0
5000
10000
15000
20000July 2012 (shortly after stabilization)October 2012April 2013 (after spring-thaw)May 2013
Control 4 in. Geocell 6 in. Geocell
Ave
rage
Cal
iforn
iabe
arin
g ra
tio in
mod
ified
subb
ase,
CB
RM
SB
10
100
1000July 2012 (shortly after stabilization)October 2012April 2013 (after spring-thaw)May 2013
Center for Earthworks Engineering Research 9
Geotextile fabrics provide separation and filtration for pavement layers
Control Non-Woven Woven
Ave
rage
Sub
base
Mod
ulus
, E
SB
-FW
D (
psi)
0
5000
10000
15000
20000July 2012 (shortly after stabilization)October 2012April 2013 (after spring-thaw)May 2013
Control Non-Woven Woven
Ave
rage
Cal
iforn
iabe
arin
g ra
tio in
mod
ified
subb
ase,
CB
RM
SB
10
100
1000July 2012 (shortly after stabilization)October 2012April 2013 (after spring-thaw)May 2013
Woven Geotextile Fabric
Non-woven Geotextile Fabric
Center for Earthworks Engineering Research 10
Polymer grids provide planar reinforcement to pavement layers
Control Biaxial Triaxial
Ave
rage
Sub
base
Mod
ulus
, E
SB
-FW
D (
psi)
0
5000
10000
15000
20000July 2012 (shortly after stabilization)October 2012April 2013 (after spring-thaw)May 2013
Control Biaxial Triaxial
Ave
rage
Cal
iforn
iabe
arin
g ra
tio in
mod
ified
subb
ase,
CB
RM
SB
10
100
1000July 2012 (shortly after stabilization)October 2012April 2013 (after spring-thaw)May 2013
Center for Earthworks Engineering Research 11
Axial Strain (in/in)
0.00 0.02 0.04 0.06 0.08 0.10 0.12 0.14 0.16
Dev
iato
r S
tres
s (p
si)
0
100
200
300
400
Unconfined Compressive Strength Test:2.5% Cement, 0.6% FP Fibers
Cement stabilization (of subbase) increases strength and stiffness. Fiber stabilization increases toughness, shear strength.
Control PC PC + FP Fiber PC + MP Fiber
Ave
rage
Sub
base
Mod
ulus
, E
SB
-FW
D (
psi)
0
10000
20000
30000
40000
50000July 2012 (shortly after stabilization)October 2012April 2013 (after spring-thaw)May 2013
Control PC PC + FP Fiber PC + MP Fiber
Ave
rage
Cal
iforn
ia b
earin
gra
tio in
sub
grad
e or
recy
cled
sub
base
, C
BR
SG
/RS
B
1
10
100
1000
10000July 2012 (shortly after stabilization)October 2012April 2013 (after spring-thaw)May 2013
All
May
201
3 D
CP
s re
ache
dre
fusa
l with
in M
SB
laye
r
FP Fibers MP Fibers
Center for Earthworks Engineering Research 12
Recycled subbase test section included 6 in. nominal subbase below modified subbase layer
Control Rec. Subbase
Ave
rage
Sub
base
Mod
ulus
, E
SB
-FW
D (
psi)
0
5000
10000
15000
20000
25000
30000July 2012 (shortly after stabilization)October 2012April 2013 (after spring-thaw)May 2013
Control Rec. Subbase
Ave
rage
Cal
iforn
ia b
earin
gra
tio in
sub
grad
e or
recy
cled
sub
base
, C
BR
SG
/RS
B
1
10
100
1000July 2012 (shortly after stabilization)October 2012April 2013 (after spring-thaw)May 2013
Center for Earthworks Engineering Research 13
Cement stabilization (of subgrade) increases strength and stiffness
Control PC
Ave
rage
Sub
base
Mod
ulus
, E
SB
-FW
D (
psi)
0
20000
40000
60000
80000July 2012 (shortly after stabilization)October 2012April 2013 (after spring-thaw)May 2013
Control PC
Ave
rage
Cal
iforn
ia b
earin
gra
tio in
sub
grad
e or
recy
cled
sub
base
, C
BR
SG
/RS
B
1
10
100
1000
10000July 2012 (shortly after stabilization)October 2012April 2013 (after spring-thaw)May 2013
Center for Earthworks Engineering Research 14
Fly ash stabilization (of subgrade) increases strength and stiffness
Con
trol
10%
FA
(Mus
catin
e)
10%
FA
(Por
t Nea
l)
15%
FA
(Am
es)
20%
FA
(Por
t Nea
l)
Ave
rage
Sub
base
Mod
ulus
, E
SB
-FW
D (
psi)
0
10000
20000
30000
40000
50000July 2012 (shortly after stabilization)October 2012April 2013 (after spring-thaw)May 2013
Con
trol
10%
FA
(Mus
catin
e)
10%
FA
(Por
t Nea
l)
15%
FA
(Am
es)
20%
FA
(Por
t Nea
l)
Ave
rage
Cal
iforn
ia b
earin
gra
tio in
sub
grad
e or
recy
cled
sub
base
, C
BR
SG
/RS
B
1
10
100
1000July 2012 (shortly after stabilization)October 2012April 2013 (after spring-thaw)May 2013
Time (minutes)
0 25 50 75 100 125 150 175 200
Res
ista
nce
(tsf
)
0
1
2
3
4
5
Ames FAMuscatine FAPort Neal FA
Initi
al S
et
Tim
e
Fin
al S
et T
ime
Set Times:Muscatine FA Initial = 107 min, Final = 170 minAmes FA Initial = 4 min, Final = 19 minPort Neal FA Initial = 3 min, Final = 6 min
Resistance at Final Set Time = 4.5 tsf
Center for Earthworks Engineering Research 15
Cement stabilized sections yielded comparatively higher modulus values overall from FWD testing
Con
trol
Mec
h. S
tab.
4 in
. Geo
cell
6 in
. Geo
cell
Non
-Wov
enW
oven
Bia
xial
Tria
xial
PC
(Sub
base
)P
C +
FP
Fib
erP
C +
MP
Fib
erR
ec. S
ubba
seP
C (S
ubgr
ade)
10%
FA
(Mus
catin
e)
10%
FA
(Por
t Nea
l)15
% F
A (A
mes
)
20%
FA
(Por
t Nea
l)
Ave
rage
Sub
base
Mod
ulus
, E
SB
-FW
D (
psi)
0
20000
40000
60000
80000July 2012 (shortly after stabilization)October 2012April 2013 (after spring-thaw)May 2013
Center for Earthworks Engineering Research 16
Cement stabilized sections yielded comparatively higher modulus values overall from DCP testing
Con
trol
Mec
h. S
tab.
4 in
. Geo
cell
6 in
. Geo
cell
Non
-Wov
en
Wov
en
Bia
xial
Tria
xial
PC
(Sub
base
)P
C +
FP
Fib
erP
C +
MP
Fib
erR
ec. S
ubba
seP
C (S
ubgr
ade)
10%
FA
(Mus
catin
e)10
% F
A (P
ort N
eal)
15%
FA
(Am
es)
20%
FA
(Por
t Nea
l)
Ave
rage
Cal
iforn
ia b
earin
gra
tio in
sub
grad
e or
recy
cled
sub
base
, C
BR
SG
/RS
B
1
10
100
1000October 2012April 2013 (after spring-thaw)May 2013
Ave
rage
Cal
iforn
iabe
arin
g ra
tio in
mod
ified
subb
ase,
CB
RM
SB
1
10
100
1000October 2012April 2013 (after spring-thaw)May 2013
ModifiedSubbase Layer
Subgrade orRecycledSubbase Layer
Center for Earthworks Engineering Research 17
Investments in foundation stabilization will increase modulus and can potentially lead to better pavement performance
0 2 4 6 8 10 12 14
Ave
rage
600
0 lb
Loa
ding
Dro
pF
WD
Ela
stic
Mod
ulus
, EF
WD
-6k (
psi)
[Ave
rage
of 9
to 3
0 te
sts]
0
20000
40000
60000
80000
4 in. Geocell
6 in. Geocell
Woven Geotextile
Nonwoven Geotextile
BX Polymer Grid
TX Polymer Grid
5% PC + 0.4% Fiberb (Subbase)
5% PC (Subbase)
10% PC (subgrade)
10% FA (Subgrade)
15% FA (Subgrade)
20% FA (Subgrade)
Average Material + Installation Cost ($/yd2)
0 2 4 6 8 10 12 14
Ave
rage
600
0 lb
Loa
ding
Dro
pF
WD
Ela
stic
Mod
ulus
, EF
WD
-6k (
psi)
[Ave
rage
of 9
to 3
0 te
sts]
0
20000
40000
60000
80000
4 in. Geocell
6 in. Geocell
Woven Geotextile
Nonwoven Geotextile
BX Polymer Grid
TX Polymer Grid
5% PC + 0.4% Fiberb (Subbase)
5% PC (Subbase)
10% PC (subgrade)
10% FA (Subgrade)
15% FA (Subgrade)
20% FA (Subgrade)
Control
(a)
(b)
Control
Note:a
Combined average for 5% PC + 0.4% FP fiber (subbase) and 5% PC + 0.4% MP fiber test sections
Note:a
Combined average for 5% PC + 0.4% FP fiber (subbase) and 5% PC + 0.4% MP fiber test sections
0 2 4 6 8 10 12 14
Ave
rage
600
0 lb
Loa
ding
Dro
p
FW
D E
last
ic M
odul
us,
EF
WD
-6k
(psi
)
[Ave
rage
of
9 to
30
test
s]
0
20000
40000
60000
80000
4 in. Geocell
6 in. Geocell
Woven Geotextile
Nonwoven Geotextile
BX Polymer Grid
TX Polymer Grid
5% PC + 0.4% Fiberb (Subbase)
5% PC (Subbase)
10% PC (subgrade)
10% FA (Subgrade)
15% FA (Subgrade)
20% FA (Subgrade)
Average Material + Installation Cost ($/yd2)
0 2 4 6 8 10 12 14
Ave
rage
600
0 lb
Loa
ding
Dro
p
FW
D E
last
ic M
odul
us,
EF
WD
-6k
(psi
)
[Ave
rage
of
9 to
30
test
s]
0
20000
40000
60000
80000
4 in. Geocell
6 in. Geocell
Woven Geotextile
Nonwoven Geotextile
BX Polymer Grid
TX Polymer Grid
5% PC + 0.4% Fiberb (Subbase)
5% PC (Subbase)
10% PC (subgrade)
10% FA (Subgrade)
15% FA (Subgrade)
20% FA (Subgrade)
Control
(a)
(b)
Control
Note:a
Combined average for 5% PC + 0.4% FP fiber (subbase) and 5% PC + 0.4% MP fiber test sections
Note:a
Combined average for 5% PC + 0.4% FP fiber (subbase) and 5% PC + 0.4% MP fiber test sections
0 2 4 6 8 10 12 14A
vera
ge 6
000
lb L
oadi
ng D
rop
FW
D E
last
ic M
odul
us, E
FW
D-6
k (
psi)
[Ave
rage
of 9
to 3
0 te
sts]
0
20000
40000
60000
80000
4 in. Geocell
6 in. Geocell
Woven Geotextile
Nonwoven Geotextile
BX Polymer Grid
TX Polymer Grid
5% PC + 0.4% Fiberb (Subbase)
5% PC (Subbase)
10% PC (subgrade)
10% FA (Subgrade)
15% FA (Subgrade)
20% FA (Subgrade)
Average Material + Installation Cost ($/yd2)
0 2 4 6 8 10 12 14
Ave
rage
600
0 lb
Loa
ding
Dro
pF
WD
Ela
stic
Mod
ulus
, EF
WD
-6k (
psi)
[Ave
rage
of 9
to 3
0 te
sts]
0
20000
40000
60000
80000
4 in. Geocell
6 in. Geocell
Woven Geotextile
Nonwoven Geotextile
BX Polymer Grid
TX Polymer Grid
5% PC + 0.4% Fiberb (Subbase)
5% PC (Subbase)
10% PC (subgrade)
10% FA (Subgrade)
15% FA (Subgrade)
20% FA (Subgrade)
Control
(a)
(b)
Control
Note:a
Combined average for 5% PC + 0.4% FP fiber (subbase) and 5% PC + 0.4% MP fiber test sections
Note:a
Combined average for 5% PC + 0.4% FP fiber (subbase) and 5% PC + 0.4% MP fiber test sections
Control PC
Ave
rage
Sub
base
Mod
ulus
, E
SB
-FW
D (
psi)
0
20000
40000
60000
80000July 2012 (shortly after stabilization)October 2012April 2013 (after spring-thaw)May 2013
0 2 4 6 8 10 12 14
Ave
rage
600
0 lb
Loa
ding
Dro
pFW
D E
last
ic M
odul
us, E
FW
D-6
k (
psi)
[Ave
rage
of 9
to 3
0 te
sts]
0
20000
40000
60000
80000
4 in. Geocell
6 in. Geocell
Woven Geotextile
Nonwoven Geotextile
BX Polymer Grid
TX Polymer Grid
5% PC + 0.4% Fiberb (Subbase)
5% PC (Subbase)
10% PC (subgrade)
10% FA (Subgrade)
15% FA (Subgrade)
20% FA (Subgrade)
Average Material + Installation Cost ($/yd2)
0 2 4 6 8 10 12 14
Ave
rage
600
0 lb
Loa
ding
Dro
pFW
D E
last
ic M
odul
us, E
FW
D-6
k (
psi)
[Ave
rage
of 9
to 3
0 te
sts]
0
20000
40000
60000
80000
4 in. Geocell
6 in. Geocell
Woven Geotextile
Nonwoven Geotextile
BX Polymer Grid
TX Polymer Grid
5% PC + 0.4% Fiberb (Subbase)
5% PC (Subbase)
10% PC (subgrade)
10% FA (Subgrade)
15% FA (Subgrade)
20% FA (Subgrade)
Control
(a)
(b)
Control
Note:a
Combined average for 5% PC + 0.4% FP fiber (subbase) and 5% PC + 0.4% MP fiber test sections
Note:a
Combined average for 5% PC + 0.4% FP fiber (subbase) and 5% PC + 0.4% MP fiber test sections
0 2 4 6 8 10 12 14
Ave
rage
600
0 lb
Loa
ding
Dro
pFW
D E
last
ic M
odul
us, E
FW
D-6
k (
psi)
[Ave
rage
of 9
to 3
0 te
sts]
0
20000
40000
60000
80000
4 in. Geocell
6 in. Geocell
Woven Geotextile
Nonwoven Geotextile
BX Polymer Grid
TX Polymer Grid
5% PC + 0.4% Fiberb (Subbase)
5% PC (Subbase)
10% PC (subgrade)
10% FA (Subgrade)
15% FA (Subgrade)
20% FA (Subgrade)
Average Material + Installation Cost ($/yd2)
0 2 4 6 8 10 12 14
Ave
rage
600
0 lb
Loa
ding
Dro
pFW
D E
last
ic M
odul
us, E
FW
D-6
k (
psi)
[Ave
rage
of 9
to 3
0 te
sts]
0
20000
40000
60000
80000
4 in. Geocell
6 in. Geocell
Woven Geotextile
Nonwoven Geotextile
BX Polymer Grid
TX Polymer Grid
5% PC + 0.4% Fiberb (Subbase)
5% PC (Subbase)
10% PC (subgrade)
10% FA (Subgrade)
15% FA (Subgrade)
20% FA (Subgrade)
Control
(a)
(b)
Control
Note:a
Combined average for 5% PC + 0.4% FP fiber (subbase) and 5% PC + 0.4% MP fiber test sections
Note:a
Combined average for 5% PC + 0.4% FP fiber (subbase) and 5% PC + 0.4% MP fiber test sections
Center for Earthworks Engineering Research 18
Correlations were made between FWD modulus and DCP penetration index
Penetration Index of Crushed LimestoneSubbase Layer, PICLS (mm/blow)
0.1 1 10 100
Ave
rage
6,0
00 lb
Loa
ding
Dro
pF
WD
Ela
stic
Mod
ulus
, EF
WD
-6k
(ps
i)1000
10000
100000
1000000October 2-3, 2012April 3, 2013
EFWD-6k = 47043 PI-0.9559
r2 = 0.6519
Penetration Index of Crushed LimestoneSubbase Layer, PICLS (mm/blow)
0.1 1 10 100
Ave
rage
14,
000
lb L
oadi
ng D
rop
FW
D E
last
ic M
odul
us, E
FW
D-1
4k (
psi)
100
1000
10000
100000
1000000 October 2-3, 2012April 3, 2013EFWD-14k = 39746 PI-1.0488
r2 = 0.6068
Penetration Index of ReclaimedSubbase, PIRSB (6 in. to 12 in.) or
Subgrade, PISG (6 in. to 12 in.) (mm/blow)
0.1 1 10 100
Ave
rage
6,0
00 lb
Loa
ding
Dro
pF
WD
Ela
stic
Mod
ulus
, EF
WD
-6k
(ps
i)
1000
10000
100000
October 2-3, 2012April 3, 2013October Best FitApril Best Fit
EFWD-6k(Oct) = 52241PI-0.3904
r2 = 0.2330
EFWD-6k(Apr) = 17801PI-0.4277
r2 = 0.5612
Penetration Index of ReclaimedSubbase, PIRSB (6 in. to 12 in.) or
Subgrade, PISG (6 in. to 12 in.) (mm/blow)
0.1 1 10 100
Ave
rage
14,
000
lb L
oadi
ng D
rop
FW
D E
last
ic M
odul
us, E
FW
D-1
4k (
psi)
1000
10000
100000
October 2-3, 2012April 3, 2013October Best FitApril Best Fit
EFWD-14k(Oct) = 41453PI-0.3385
r2 = 0.2058
EFWD-14k(Apr) = 17006PI-0.4431
r2 = 0.5438
(a)
(b)
(c)
(d)
Control PC
Ave
rage
Sub
base
Mod
ulus
, E
SB
-FW
D (
psi)
0
20000
40000
60000
80000July 2012 (shortly after stabilization)October 2012April 2013 (after spring-thaw)May 2013
Control PC
Ave
rage
Sub
base
Mod
ulus
, E
SB
-FW
D (
psi)
0
20000
40000
60000
80000July 2012 (shortly after stabilization)October 2012April 2013 (after spring-thaw)May 2013
Modified Subbase Layer Subgrade or Recycled Subbase Layer
Center for Earthworks Engineering Research 19
Multivariate statistical analyses showed that the surface subbase elastic modulus layer becomes statistically insignificant during the spring thaw
Term Estimate Standard Error t Ratio Prob. > t Statistically
Significant R2 Adj.
October 2012 Testinglog(EFWD) = b0 + b1∙log(PICLS) + b2∙log(PISG or RSB)
bo 10.469031 0.112847 92.77 <0.0001 Yes0.520b1 -0.561766 0.144323 -3.89 0.0002 Yes
b2 -0.194888 0.054533 -3.57 0.0007 YesApril 2013 (Spring Thaw) Testinglog(EFWD) = b0 + b1∙log(PICLS) + b2∙log(PISG or RSB)
bo 9.2933905 0.243899 38.10 <0.0001 Yes0.69b1 0.215623 0.128841 1.67 0.0991 No
b2 -0.546244 0.046481 -11.75 <0.0001 Yes
Center for Earthworks Engineering Research 20
A summary of key findings are as follows:
• During spring thawing, each test section experienced approximately 2 to 9 times reduction in FWD modulus or CBR
• Cement stabilized sections perform comparatively better than all other test sections, according to FWD and CBR measurements
• Investments in pavement foundation stabilization techniques can potentially result in better pavement performance, even during spring thawing
• Elastic modulus of surface granular layers become statistically insignificant to overall modulus during spring thaw
Center for Earthworks Engineering Research 21
Performance of the stabilized foundations will be monitored in the near and distant future
• Sections were paved with, PCC, HMA, and WMA this summer
• Long term performance study• Laboratory studies (In progress)
Center for Earthworks Engineering Research 22
Acknowledgments
The presenters would like to thank…• The Iowa Department of Transportation
• Mark Dunn, P.E.• Jesus Rodriguez
• Center for Earthworks Engineering Research (CEER) students• Lance Keltner• Nick Buse• Jinhui Hu• Yang Zhang
Thank You for your attention!
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