Post on 12-Apr-2018
Evaluation of Evaluation of SubgradeSubgradeStabilization on Pavement Stabilization on Pavement
PerformancePerformance
Louisiana Transportation Research CenterLouisiana Transportation Research Center
Mark Morvant, P.E.Mark Morvant, P.E.Pavement & Geotechnical Research AdministratorPavement & Geotechnical Research Administrator
Lime Treated Working Table
Subgrade
Dry Embankment
Subgrade
Existing Subgrade
New Embankment
Saturated
DryClay
Silt
Usable soils
High silt soils (no silt restriction)
SubgradeSubgrade TreatmentTreatment
Treated Layer
Treated Layer
SubgradeSubgrade PropertiesProperties
lSoil Type– Heavy Clay– Lean clay– Silt
lSoil Condition– Wet– Optimum– Dry
lStabilization Agents– Cement– Lime– Lime/Fly Ash– Cement/Slag
Identification and Identification and Stabilization Methods for Stabilization Methods for
Problematic Silt SoilsProblematic Silt SoilsCivil & Environmental Engineering DepartmentCivil & Environmental Engineering Department
University of New OrleansUniversity of New Orleans
Principal InvestigatorsPrincipal InvestigatorsKenneth Kenneth McManisMcManis, Ph.D., P.E., Ph.D., P.E.
MysoreMysore NatarajNataraj, Ph.D., P.E., Ph.D., P.E.
Sponsored by Louisiana Transportation Research Center
Cyclic Stress-Strain Curves
0
500
1000
1500
2000
2500
3000
0 5 10 15 20 25
Strain, %
App
lied
Loa
d, p
sf
Acadia Soil
Chase Brown Soil
Chase White Soil
DeRidder Brown Soil
DeRidder White Soil
Natchitoches K2 Soil
ALF UU Tests
ALF CD Test
UNO Research StudyUNO Research StudyHigh Silt SoilsHigh Silt Soils
15 psi
35 psi
37 psi
5 psi
(+4% opt)
Silt content 50 %
5 psi
20 psi
50 psi
90 psi
150 psi
(+4% opt)
Silt content 50 %
70% Silt
lime
Lime/fly ash
CementUntreated
Slag Cement
High Silt / High MoistureHigh Silt / High Moisture
High Silt / High MoistureHigh Silt / High Moisture
lime
Cement
Lime/fly ash
LTRC Guideline Recommendation
In-Place SubgradesCement Treatment Subgrades - Soils identified with a silt
content of 50 percent or greater and also a PI of 10 or less.
Lime Treated Subgrades – Wet soils identified with a PI greater than 15.
Evaluation of a Evaluation of a SubbaseSubbaseLayer on Pavement Layer on Pavement
PerformancePerformancel Laboratory Evaluation
– Doc Zhang– Louay Mohommad
l Field Evaluation– Gavin Gautreau– Kevin Gaspard– District Laboratory Engineers
l Accelerated Loading Evaluation– Masood Rasoulian– Bill King
l Numerical Analysis (proposed)– Freddy Roberts (LTU)– Murad Abu-Farsakh– Louay Mohammad
Laboratory ProgramLaboratory Program
l Subgrade soils– Silt> 65% PI<10– Silty Clay PI 10 – 25– Heavy Clay PI > 25
l Moisture conditions– Wet– Optimum– Dry
l Stabilization additives– Portland Cement– Lime– Lime / fly ash
l Characterization– Gradation– Atterberg limits– Eades and Grim pH test (lime)
l Strength testing– Unconfined compression– Triaxial tests– Resilient modulus– CBR
l Durability– Long term fatigue (rut)– Wet dry cycles– Tube Suction Test
Field Test ProgramField Test Program
l Silt subgrade test sections PI<11– Cement treated working table– Lime treated working table– Cement stabilized subgrade– Lime/fly ash stabilized subgrade
l Clay subgrade test sections PI: 10 – 25– Cement stabilized subgrade– Lime stabilized subgrade– Lime/fly ash stabilized subgrade
l Heavy clay soil test sections PI > 25– Lime treated working table– Lime stabilized subgrade– Lime/fly ash stabilized subgrade
Falling WeightDeflectometer
Field Evaluation EquipmentField Evaluation Equipment
Dynamic Cone Penetrometer
-40.0
-30.0
-20.0
-10.0
0.0
10.0
20.0
30.0
0 50 100 150 200 250 300
Blow Count
Cumu
lative
Penet
ration
, cm
-40.0
-30.0
-20.0
-10.0
0.0
10.0
20.0
30.0
0 50 100 150 200 250 300
Blow CountCu
mulat
ive Pe
netrat
ion, c
m
Dynamic Cone Dynamic Cone PenetrometerPenetrometer
Stone
Cement TreatedSubgrade
Compacted Embankment
Blow count Blow count
Dep
th(c
m)
Dep
th
0
20
40
60
10
30
50
70
Dep
th
0
20
40
60
10
30
50
70
5 mm/blow
1 mm/blow
7 mm/blow
Dep
th(c
m)
0
1020
30
4050
60
7080
0 10 20 30 40 50 60 70 80 90 100 110 120
DCP BlowsDe
pth
(cm
)
Stone Base
Lime Treated Subgrade
2.5 mm/blow
20 mm/blow
80 mm/blow
Falling Weight Falling Weight DeflectometerDeflectometer
Aggregate Base
Treated Subgrade
Cement TreatedCement TreatedWorking Table DesignWorking Table Design
LA 182 / LA 89LA 182 / LA 89St. Landry ParishSt. Landry Parish
LA 182 / LA 89LA 182 / LA 89BeggsBeggs to Parish Lineto Parish Line
St. Landry ParishSt. Landry Parish
Log mile
Log mile
Log mile
Log mile
Log mile
LA 182LA 97
Silt Pumping Criteria
LA 182 / LA 89LA 182 / LA 89BeggsBeggs to Parish Lineto Parish Line
St. Landry ParishSt. Landry Parish
Pumping Subgrade
3.5” Asphalt pavement
12” Lime TreatedWorking Table (10%)
12” Cement TreatedWorking Table (4%)
12” Cement Treated Base ( 6%)
Firm Subgrade
LA 182/97 Test SectionsLA 182/97 Test Sections1. Cement treated clay subgrade: 30+00 – 40+862. Lime treated clay subgrade : 40+85 – 53+053. Lime treated silt subgrade : 494+44 – 505+934. Cement treated silt subgrade 506+61 – 546+27
LA 182LA 97
1 2
3 4
Untreated Zone
Silt Pumping Criteria
Log mile
Log mile
Log mile
Log mile
Log mile
LA 182/97 Test SectionsLA 182/97 Test Sections
0
50
100
150
200
250
300
350
03/20/03 06/28/03 10/06/03 01/14/04 04/23/04 08/01/04 11/09/04
FWD
mod
ulus
(ks
i)
Cement treated silt subgrade
Lime treated silt subgrade
Untreated silt subgradeCement treated silty
clay subgrade
Lime treated silty clay subgrade
LA 182 Test SectionsLA 182 Test SectionsDCP Strength ValuesDCP Strength Values
0
2
4
6
8
10
12
12/27/03 3/17/04 6/5/04 8/24/04 11/13/04
DC
P (m
m/b
low
)
Lime Treated Silt (10%)
Cement Treated Silt (4%)
Lime Treated Clay (10%)
Untreated Firm Silt
Cement Treated Clay (4%)
SubgradeSubgrade Treatment vs. Treatment vs. SubgradeSubgrade StabilizationStabilization
l Subgrade Treatment– Construction Aid– Standardized Design– Quality not as important– Temporary Performance– Less costs– Faster to construct
l Subgrade Stabilization– Enhances pavement
performance– Requires laboratory design– Construction Quality
important– More expensive– May require more time to
construct
High Silt High Silt SubgradesSubgradesLaboratory ResultsLaboratory Results
Silt subgrade (65%) - 7 day strength
0
100
200
300
400
10 15 20 25 30
Moisture content at preparation, %
Unc
onfi
ned
com
pres
sive
str
engt
h,
psi
10% Lime Natural
+4 % +8%OptimumMoisture
4% Cement
8% Cement
12% Cement
Laboratory ResultsLaboratory ResultsHigh Silt SoilsHigh Silt Soils
Silt Subgrade 65% - 28 day strength
0
100
200
300
400
500
5 10 15 20 25
Mositure Content, %
UC
S, p
si
10% Lime
4% Cement
8% Cement
12% Cement
OptimumMoisture +4% +8%
SiltySilty ClayClayLaboratory ResultsLaboratory Results
Clay Subgrade (PI=22) - 7 day strength
0
100
200
300
400
500
600
5 10 15 20 25
Moisture Content at molding, %
Unc
onfi
ned
Com
pres
sive
Str
ench
, ps
i
Optimum moisture +4% +8%
4% Cement
8% Cement
12% Cement
Untreated
0
50
100
150
200
250
300
2 4 6 8 10
Cement Percentage
UC
C S
tren
gth
(p
si)
124 psi
172 psi
252 psi
32 psi
72 psi38 psi73 psi
104 psi
Optimum moisture
4% above optimum moisture
6% lime application24 hrs prior to cement
Seven Day Strength Test Results(Dist. 07 Lab Results)
US 171 Subgrade Soils75 % silt
US 171 Test SectionsUS 171 Test SectionsCement Treated Natural Cement Treated Natural
SubgradeSubgrade (8%)(8%)
0
10
20
30
40
50
60
70
0 5 10 15 20 25 30
Days
DCP (m
m/b
low
)
122+50125+00127+50untreateduntreateduntreated
3 mm/blow
High Silt High Silt SubgradeSubgrade• Cement Treatment
• 9% by volume by bid specification 305• Adjusted by engineer as conditions warrant
• Cement & Cement / Slag Stabilization• Designed for maximum benefit• Strength requirement
• 7 day cure strength• Target strength value
• Lime – fly ash (incomplete)• Eades & Grimes for lime content• Strength target value for fly ash content
• Moisture sensitivity (incomplete)• Tube suction test• Capillary soak
Heavy Clay Heavy Clay SubgradeSubgrade
• Lime Treatment• Generally 10% by volume• Adjusted by engineer as conditions warrant
• Lime Stabilization• Designed for maximum benefit• Strength requirement
• Natural cure vs. accelerated cure• Target strength value
• Moisture sensitivity• Tube suction test• Capillary soak
EadesEades & Grimes Test& Grimes TestLime Requirement for StabilizationLime Requirement for Stabilization
Heavy Clay PI = 47Heavy Clay PI = 47
7
8
9
10
11
12
13
0.0% 10.0% 20.0% 30.0% 40.0%
Lime content by volume, %
ph
val
ue
pH = 12.4
Lime Content = 18% by volume (7.5% by weight)
Lime Treated Heavy ClayLime Treated Heavy ClayAccelerated Cure Accelerated Cure vsvs Natural CureNatural Cure
Heavy Clay, 18% lime
0
20
40
60
80
100
120
140
25 27 29 31 33 35 37 39 41 43 45
Moisture Content, %
UC
S, p
si
28day curing 7day acceleration curing
OptimumMoisture
Target value
Add water during mixing
Add additional limeto reduce moisture
Heavy Clay Heavy Clay SubgradeSubgradeLime StabilizationLime Stabilization
Preliminary RecommendationsPreliminary Recommendations
l pH Test for full lime reaction – Eades & Grimes Test
l Unconfined compression test for minimum strength – Target value 100 psi – 125 psi– Minimum 50 psi increase from untreated
l Specifications for maximum performance– Mellowing period– Additional lime based on in situ moisture– Double application if necessary
Current Current SubgradeSubgrade Treatment Treatment PolicyPolicy
(Working Table )(Working Table )
l Item 304 Lime Treatment– Type D compacted to the satisfaction of the
engineer– Type E compacted to 95% density – Generally 10% by volume
l S-Item Cement Treatment– Refers to Item 305 Subgrade Layer– By specification: 9% by volume
Forthcoming Research ResultsForthcoming Research Results
SN = a1 d1 D1 + a2 d2 D2 + a3 d3 D3 + … ai di Di
a: Structural Coefficientd: Drainage Coefficient (d = .9)D: Thickness of Pavement Layer
Asphalt Base Course a2 = .33
Asphalt Pavement a1 = .44
Treated Subgrade a4 = 00
Stone Base a3 = .14Cement Treated Base a3= .10
D1
D2
D3
D4
Subgrade Mr = ??
Can this layer be counted on for long term structural support?
l Design Process– DOTD pre-design– DOTD post bid design– Contractor post bid design
l Stabilization Quantity– Unconfined Compressive Strength Target Value– Standardized Design on Soil Properties– Long term moisture sensitivity
l Construction Specifications– QC/QA– Meets target value– Construction damage– Traffic damage
Research Result Research Result Guidelines Guidelines
Saturated Silt Subgrade
Test Lane 1Standard ConstructionCement Treated Base
Lime Treated Working Table
2” Asphalt pavement 2” Asphalt pavement
12” Lime Treated Subgrade (10%) 12” Cement Treated Subgrade (8%)
8.5” Stone Base8.5” Stone Base
Water source
Test Lane 2Cement Treated Base
Cement Treated Subbase
ALF ExperimentALF Experiment
Potential ImpactPotential ImpactLife Cycle AnalysisLife Cycle Analysis
0 15 30 45
Construction$114,000/ln mi
Mill & Overlay$67,000
Mill & Overlay$67,000
0 15 30 45
Construction$96,000/ln mi
Mill & Overlayminor patching$75,000/ln mi
Reconstruction$96,000/ln mi
Mill & Overlay$67,000/ln mi
Salvage Value$33,000/ln mi
Annualized cost = $14,300/ln mi/yr
Annualized cost = $11,780/ln mi/yr
20 %
Questions?Questions?
Stone Interlayer Base over Stone Interlayer Base over SubgradeSubgrade TreatmentTreatment
12” Treated Subgrade(Subbase)
Subgrade Soils
2.0” AC -Wearing Course
2.5” AC – Binder Course
4” Stone Base
10” Cement Treated Base(a = .10)
Stone Interlayer Base
Cement Treated Base•300 psi min.•Opt moisture•construction control
Subbase
•Treatment options•Cement•Lime•Lime / Fly Ash
•Existing Moisture Condition•Opt•Wet
• 75 - 100 psi•Construction control ?