unsaturated soil variations, may 2003
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A Laboratory Technique for Estimating A Laboratory Technique for Estimating the Resilient Modulus Variation of the Resilient Modulus Variation of
Unsaturated Soil Specimens from CBR Unsaturated Soil Specimens from CBR and Unconfined Compression Testsand Unconfined Compression Tests
byby: : Mike VogrigMike Vogrig
Adam McDonaldAdam McDonald
Presented toPresented toCivil Engineering DepartmentCivil Engineering DepartmentLakehead University, CanadaLakehead University, Canada
OutlineOutline
IntroductionIntroductionScopeScopeProcedureProcedureResultsResultsRecommendationsRecommendationsConclusionsConclusions
OutlineOutline
IntroductionIntroductionScopeScopeProcedureProcedureResultsResultsRecommendations Recommendations ConclusionsConclusions
IntroductionIntroduction
Pavement system compositionPavement system composition
Asphalt /Concrete
Granular Base
Sub-base
Sub-grade
IntroductionIntroduction
Question: Pavement Design Method????Question: Pavement Design Method????
Key Soil Properties:Key Soil Properties:CBR values CBR values RR--values values Resilient Modulus, Resilient Modulus, MMrr
MechanisticMechanistic--Empirical Design Method Empirical Design Method (ME)(ME)
CBR ValuesCBR ValuesIndicates: Indicates:
–– the soil’s resistance to forcethe soil’s resistance to force–– the swell and strength potential the swell and strength potential
of soilsof soilsUsed to determine:Used to determine:
–– Resilient modulus (Resilient modulus (MMrr))–– RR-- valuesvalues
CBR tests incorporate the effects of the CBR tests incorporate the effects of the asphalticasphalticlayer by placing the appropriate surcharge on the layer by placing the appropriate surcharge on the samplesample
RR--ValuesValues
Indicates the ability to resist lateral Indicates the ability to resist lateral deformationdeformation
Determining the expansion pressure of a Determining the expansion pressure of a soil gives the thickness of the material soil gives the thickness of the material above the soil that will prevent swellingabove the soil that will prevent swelling
Indirect method of determining Indirect method of determining MMrr::MMrr (MPa) = 8.0 + (3.8 x R(MPa) = 8.0 + (3.8 x R--value)value)MMrr ((psipsi) = 1000 + (555 x R) = 1000 + (555 x R--value)value)
Resilient Modulus (Resilient Modulus (MMrr))
Primary soil property: Dynamic testPrimary soil property: Dynamic test
Defined as the ratio between repeated deviator Defined as the ratio between repeated deviator stress and resilient strain:stress and resilient strain:
MMrr = (= (σσ11-- σσ33) / ) / εεalal
Calculated by: Calculated by: MMrr (MPa) = 10.342 (CBR)(MPa) = 10.342 (CBR)
MMrr ((psipsi) = 1500 (CBR) ) = 1500 (CBR)
Laboratory Setup for Laboratory Setup for MMrr
Specimen Specimen For aggregate baseFor aggregate base
Diameter: 6”; Height: 12”Diameter: 6”; Height: 12”Stress hardening for granular materialsStress hardening for granular materials
For subgrade soilsFor subgrade soilsDiameter: 2.8”; Height: 6”Diameter: 2.8”; Height: 6”Stress softening for fine grained materialsStress softening for fine grained materials
Test protocol: LTPP PTest protocol: LTPP P-- 4646
Testing Equipment for Testing Equipment for MMrr
Typical Triaxial Test ResultsTypical Triaxial Test Results
OutlineOutline
IntroductionIntroduction
ScopeScopeProcedureProcedureResultsResultsRecommendations Recommendations ConclusionsConclusions
ScopeScope
Determine correlations between California Bearing Determine correlations between California Bearing Ratio (CBR) tests and unconfined compression Ratio (CBR) tests and unconfined compression tests (UCS) on unsaturated soils and propose a tests (UCS) on unsaturated soils and propose a simple technique for estimating simple technique for estimating MMrr
Soil supplied by the Minnesota Department of Soil supplied by the Minnesota Department of Transportation (Mn DOT) was used in test programTransportation (Mn DOT) was used in test program
MnMn--DOT Full Scale Test FacilityDOT Full Scale Test Facility
Site Map of MnSite Map of Mn--DOT Test FacilityDOT Test Facility
MnRoadMnRoad Bedrock GeologyBedrock Geology
OutlineOutline
IntroductionIntroductionScopeScopeProcedureProcedureResultsResultsRecommendations Recommendations ConclusionsConclusions
Grain Size Analysis DataGrain Size Analysis Data
0.010.1110Particle Size (mm)
0
20
40
60
80
100
Perc
ent P
assi
ng (%
)
Modified CBR Testing ProcedureModified CBR Testing Procedure
Soil dried to 0% w.c.Soil dried to 0% w.c.Mixed 16% w.c.Mixed 16% w.c.Rest for 24 hoursRest for 24 hoursCompacted in 5 layers, 56 Compacted in 5 layers, 56 blows per layerblows per layer
Initial density and w. c: Saturated sampleInitial density and w. c: Saturated sampleDry the sample under two Dry the sample under two –– 40 watt lights40 watt lightsOne week in constant moisture roomOne week in constant moisture roomTest conductedTest conductedDegree of saturation determinedDegree of saturation determined
CBR Test ResultsCBR Test Results
0
4
8
12
16
20
020406080100Degree of Saturation (%)
CB
R R
esul
ts.
CBRBest f it line (CBR)
Analysis: CBR ResultsAnalysis: CBR Results
0.0
0.2
0.4
0.6
0.8
1.0
020406080100% Saturation
Nor
mal
ized
Res
ults
Modified UCS Testing ProcedureModified UCS Testing Procedure
Drying the samples using Drying the samples using twotwo-- 40 watt lamps40 watt lamps
Prepared according to AASHTO designation T 208, Prepared according to AASHTO designation T 208, Unconfined Compression Strength of Cohesive SoilsUnconfined Compression Strength of Cohesive SoilsModifications:Modifications:
Sample Preparation – creating unsaturated conditions
Unconfined Compression Test Unconfined Compression Test Results Results –– Varying TimesVarying Times
0200400600800
10001200140016001800
0.0 1.0 2.0 3.0 4.0 5.0 6.0 7.0
Unit Strain (x 10-2)
Stre
ss (k
Pa)
16 hr (24.8%)11 hr (32.5%)
6 hr (56.0%)
4 hr (68.5%)2 hr (79.8%)1 hr (82.2%)
Unconfined Compression Test Unconfined Compression Test ResultsResults
0
200
400
600
800
1000
1200
1400
1600
1800
2000
020406080100% Saturation
CBR
Res
ults
UCS
Best f it line (UCS)
Analysis: UCS ResultsAnalysis: UCS Results
0.0
0.2
0.4
0.6
0.8
1.0
020406080100Degree of Saturation (%)
Nor
mal
ized
UC
S R
esul
ts.
CBR and UC ComparisonCBR and UC Comparison
0.0
0.2
0.4
0.6
0.8
1.0
020406080100Degree of Saturation (%)
Nor
mal
ized
Res
ults
CBRUCS
Comparison of CBR and UCSComparison of CBR and UCS
0
4
8
12
16
20
020406080100Degree of Saturation (%)
CB
R R
esul
ts
0
400
800
1200
1600
2000
UC
S R
esults (kPa).
CBRUCSBest f it line (UCS)Best f it line (CBR)
OutlineOutline
IntroductionIntroductionScopeScopeProcedureProcedureResultsResults
Recommendations Recommendations ConclusionsConclusions
RecommendationsRecommendationsLonger equilibrium time for CBR molds in Longer equilibrium time for CBR molds in moisture control room before testing in order to moisture control room before testing in order to achieve uniform water contents.achieve uniform water contents.
Direct Direct MMrr testing procedures to eliminate errors testing procedures to eliminate errors with regards to the mathematical CBRwith regards to the mathematical CBR--MMrr
correlations.correlations.
A better understanding to incorporate the principles A better understanding to incorporate the principles of unsaturated soils behavior in the mathematical of unsaturated soils behavior in the mathematical relationship relating unconfined compression test relationship relating unconfined compression test results and results and MMrr values values
OutlineOutline
IntroductionIntroductionScopeScopeProcedureProcedureResultsResultsRecommendations Recommendations ConclusionsConclusions
ConclusionsConclusions
Research Study: PromisingResearch Study: Promising
This method of testing could be a useful technique in This method of testing could be a useful technique in relating simple soil properties to more complex soil relating simple soil properties to more complex soil parameters such as resilient modulus values used in the parameters such as resilient modulus values used in the design of pavements.design of pavements.
Strong relationship: Correlations between the test dataStrong relationship: Correlations between the test data
More testing and large database is required for proposing More testing and large database is required for proposing such correlations.such correlations.
AcknowledgementsAcknowledgements
We’d like to the the following for their We’d like to the the following for their guidance and support:guidance and support:
–– Dr. S.K. VanapalliDr. S.K. Vanapalli–– Conrad Conrad HagstromHagstrom–– MnMn--DOTDOT–– Molson CanadianMolson Canadian
Thank YouThank You
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