A Laboratory Technique for Estimating the Resilient Modulus Variation of Unsaturated Soil Specimens from CBR and Unconfined Compression Tests

Transcription

1 A Laboratory Technique for Estimating the Resilient Modulus Variation of Unsaturated Soil Specimens from CBR and Unconfined Compression Tests by: Mike Vogrig Adam McDonald Presented to Civil Engineering Department Lakehead University, Canada

2 Outline Introduction Scope Procedure Results Recommendations Conclusions

3 Outline Introduction Scope Procedure Results Recommendations Conclusions

4 Introduction Pavement system composition Asphalt /Concrete Granular Base Sub-base Sub-grade

5 Introduction Question: Pavement Design Method???? Key Soil Properties: CBR values R-values Resilient Modulus, Mr Mechanistic-Empirical Design Method (ME)

6 CBR Values Indicates: the soil s resistance to force the swell and strength potential of soils Used to determine: Resilient modulus (M( r ) R- values CBR tests incorporate the effects of the asphaltic layer by placing the appropriate surcharge on the sample

7 R-Values Indicates the ability to resist lateral deformation Determining the expansion pressure of a soil gives the thickness of the material above the soil that will prevent swelling Indirect method of determining M r : M r (MPa) = (3.8 x R-value) R M r (psi)) = (555 x R-value) R

8 Resilient Modulus (M( r ) Primary soil property: Dynamic test Defined as the ratio between repeated deviator stress and resilient strain: Mr = (σ1-( σ3) ) / ε al Calculated by: Mr (MPa) = (CBR) Mr (psi)) = 1500 (CBR)

9 Laboratory Setup for M r Specimen For aggregate base Diameter: 6 ; Height: 12 Stress hardening for granular materials For subgrade soils Diameter: 2.8 ; Height: 6 Stress softening for fine grained materials Test protocol: LTPP P-P 46

10 Testing Equipment for M r

11 Typical Triaxial Test Results

12 Outline Introduction Scope Procedure Results Recommendations Conclusions

13 Scope Determine correlations between California Bearing Ratio (CBR) tests and unconfined compression tests (UCS) on unsaturated soils and propose a simple technique for estimating M r Soil supplied by the Minnesota Department of Transportation (Mn DOT) was used in test program

14 Mn-DOT Full Scale Test Facility

15 Site Map of Mn-DOT Test Facility

16 MnRoad Bedrock Geology

17 Outline Introduction Scope Procedure Results Recommendations Conclusions

18 Grain Size Analysis Data 100 Percent Passing (%) Particle Size (mm) 0.01

19 Modified CBR Testing Procedure Soil dried to 0% w.c. Mixed 16% w.c. Rest for 24 hours Compacted in 5 layers, 56 blows per layer Initial density and w. c: Saturated sample Dry the sample under two 40 watt lights One week in constant moisture room Test conducted Degree of saturation determined

20 CBR Test Results CBR Results CBR Best fit line (CBR) Degree of Saturation (%) 20 0

21 Analysis: CBR Results 1.0 Normalized Results % Saturation 20 0

22 Modified UCS Testing Procedure Drying the samples using two- 40 watt lamps Prepared according to AASHTO designation T 208, Unconfined Compression Strength of Cohesive Soils Modifications: Sample Preparation creating unsaturated conditions

23 Unconfined Compression Test Results Varying Times Stress (kpa) Unit Strain (x 10-2 ) 16 hr (24.8%) 11 hr (32.5%) 6 hr (56.0%) 4 hr (68.5%) 2 hr (79.8%) 1 hr (82.2%)

24 Unconfined Compression Test Results CBR Results UCS Best fit line (UCS) % Saturation 20 0

25 Analysis: UCS Results Normalized UCS Results Degree of Saturation (%) 20 0

26 CBR and UC Comparison CBR Normalized Results UCS Degree of Saturation (%) 20 0

27 Comparison of CBR and UCS CBR Results CBR UCS Best fit line (UCS) Best fit line (CBR) UCS Results (kpa) Degree of Saturation (%) 0 0

28 Outline Introduction Scope Procedure Results Recommendations Conclusions

29 Recommendations Longer equilibrium time for CBR molds in moisture control room before testing in order to achieve uniform water contents. Direct Mr testing procedures to eliminate errors with regards to the mathematical CBR-Mr correlations. A better understanding to incorporate the principles of unsaturated soils behavior in the mathematical relationship relating unconfined compression test results and M r values

30 Outline Introduction Scope Procedure Results Recommendations Conclusions

31 Conclusions Research Study: Promising This method of testing could be a useful technique in relating simple soil properties to more complex soil parameters such as resilient modulus values used in the design of pavements. Strong relationship: Correlations between the test data More testing and large database is required for proposing such correlations.

32 Acknowledgements We d like to the the following for their guidance and support: Dr. S.K. Vanapalli Conrad Hagstrom Mn-DOT Molson Canadian

33 Thank You