Backcalculated subgrade resilient modulus design values for the State of Michigan.

by Tyler Allen Dawson

The resilient modulus (MR) of roadbed soils is an important input required for the design of pavement structures. The MR is a fundamental soil property reflecting the soil response to the applied stresses. The MR of a given roadbed soil is dependent on the soil type, water content, dry density, particle gradation and angularity, and stress states. The latter is a function of the pavement layer thicknesses and stiffness. The implication of the above is that for a given soil type and stress level, the MR of the soil is independent of the type of pavement surface (such as concrete, asphalt, or composite) and the type of testing procedure conducted (triaxial cyclic loading or Falling Weight Deflectometer (FWD) testing).;The Michigan Department of Transportation (MDOT) sponsored this study to characterize the MR of the roadbed soils in the State of Michigan. Laboratory tests were conducted to develop average MR values, by soil type, and correlations to simple tests (Sessions 2008). FWD tests were conducted and pavement layer moduli were backcalculated to determine roadbed soil MR. The MR results were very similar between laboratory and field testing, and between flexible and rigid pavements.

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