United States Department of Transportation
i
Measurement and Evaluation of Subgrade Soil Parameters: Phase I – Synthesis of Literature
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2009-09-01
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Abstract:A key material property used in the mechanistic-empirical pavement design guide (MEPDG) is the resilient modulus (M sub r), which either can be obtained from experimental testing or can be backcalculated from other measured soil properties. The determination of a representative M sub r value for a given subgrade, considering seasonal variations and testing intricacies, is not an easy or straightforward task. Over 30 different correlation equations were reviewed in this study. Selected equations were further examined using data from two Montana Department of Transportation (MDT) soil survey reports. Results from the literature review and preliminary data evaluation indicate there is little to no consistency between equations for predicting M sub r from soil index and classification properties. Most of the equations were developed from relatively small sample sets and often for region-specific soil types. Until a more detailed assessment is conducted, the authors discourage the general use of M sub r correlation equations without prior testing and verification of the suitability and reliability of the modulus estimates. The authors suggest that full scale implementation of a repeated load triaxial testing program for the determination of M sub r on a routine project basis may not be the most cost effective approach for MDT. Rather, it is recommended that additional evaluation of MDT soil survey data be conducted to identify potentially useful correlation equations and to identify the soil parameters that may be most denotative of soil stiffness. A subsequent phase of focused repeated load triaxial testing could then be conducted in an efficient manner to measure M sub r for specific soil types and to verify the suitability and applicability of previously identified correlation equations.
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