Evaluation of Subgrade Moduli for Flexible Pavements in Virginia: Final Report

About the report:

Advances in pavement design technology in recent years have led to more dependence on mechanistic approaches and less reliance on subjective design criteria. In Virginia, the tendency is toward a pavement design and evaluation methodology based on elastic design theories. Underlying this design approach is a need to determine the elastic properties of paving materials. These properties had been evaluated for materials other than subgrade soils in earlier research. Thus the purpose of the present research was to determine the elastic moduli of Virginia subgrade soils and to provide designers with a range of moduli values that might be used in design evaluations. The project was only partially successful because of unidentified factors that appear to have significant effects on the elastic moduli of subgrade soils. Nevertheless, the study showed that within the statistical limitations set forth in the report, the elastic moduli of subgrade soils can be estimated from information routinely collected at the time the preliminary engineering soil survey is. conducted on a proposed highway construction project. The factors having statistically significant impacts on subgrade elastic moduli were determined to be the dry density and the gradation, particularly the percentage passing the No. 200 sieve, of the soil. Contrary to expectations, there was no significant relationship between the California bearing ratio and subgrade modulus. Because of the possibility of large errors in estimating the elastic modulus from the prediction equations developed, the reader is cautioned to use those predicted values as guidelines only in the absence of further data.

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