Relationship Between Backcalculated and Laboratory-Measured Resilient Moduli of Unbound Materials

Gerardo W. Flintsch, Imad L. Al-Qadi, Youngjin Park, Thomas L. Brandon, Alexander Appea

Research output: Contribution to journalArticlepeer-review


The resilient moduli of an unbound granular subbase (used at the Virginia Smart Road) obtained from laboratory testing were compared with those backcalculated from in situ falling weight deflectometer deflection measurements. Testing was performed on the surface of the finished subgrade and granular subbase layer shortly after construction. The structural capacity of the constructed subgrade and the depth to a stiff layer were computed for 12 experimental sections. The in situ resilient modulus of the granular subbase layer (21-B) was then backcalculated from the deflections measured on top of that layer. The backcalculated layer moduli were clearly stress-dependent, showing an exponential behavior with the bulk stress in the center of the layer. Resilient modulus test results of laboratory-compacted specimens confirmed the stress dependence of the subbase material modulus. Three resilient modulus models were fitted to the data. Although all three models showed good coefficients of determination (R2 > 90%), the K-θ model was selected because of its simplicity. The correlation between field-backcalculated and laboratory-measured resilient moduli was found to be strong. However, when the stress in the middle of the layer was used in the K-θ model, a shift in the resilient modulus, θ, was observed. This finding suggests that a simple shift factor could be used for the range of stress values considered.

Original languageEnglish (US)
Pages (from-to)177-182
Number of pages6
JournalTransportation Research Record
Issue number1849
StatePublished - Jan 1 2003
Externally publishedYes

ASJC Scopus subject areas

  • Civil and Structural Engineering
  • Mechanical Engineering

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