unsaturated soil variations, may 2003

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