United States Department of Transportation
i
Resilient Modulus Prediction Models of Unbound Materials for Nevada
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2018-06-26
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[PDF-3.16 MB]
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Abstract:The American Association of State Highway and Transportation Officials (AASHTO) adopted the Mechanistic-Empirical Pavement Design Guide (MEPDG) as an interim pavement design standard in 2008. In 2015, the Nevada Department of Transportation (NDOT) implemented the MEPDG for the structural design of new and rehabilitated flexible pavements. The resilient modulus of the unbound materials remains an important parameter in pavement design. This parameter also used to characterize the unbound materials in the MEPDG. The MEPDG follows a hierarchical approach in defining the required engineering properties of the pavement structure. Three levels of input are specified in the AASHTOWare Pavement ME design software. This includes direct measurement from the laboratory testing offering the highest level of accuracy (i.e., Level 1), estimated values using correlations with soil properties (i.e., Level 2), and typical values offering the lowest level of accuracy (i.e., Level 3). NDOT currently uses R-value to estimate the resilient modulus of unbound materials which is not originally developed for Nevada. The major objective of this study is to develop a new resilient modulus prediction model for use in pavement rehabilitation designs. Unbound materials (i.e., base, borrow, and subgrade) were sampled from several locations throughout Nevada and various tests were conducted to determine unbound material properties and characteristics, including the classification of the evaluated material (i.e., soil classification), R-value, moisture-density relationships, and resilient modulus testing. The resilient modulus test was conducted according to AASHTO T307 procedure. Prediction models for all three unbound material types (i.e., base, borrow, and subgrade) correlating resilient modulus to R-value and other physical properties were developed for pavement rehabilitation designs. District 1 materials were used to develop these prediction models, and the District 2 and District 3 materials were used to verify the models. Additionally, it was concluded that the current available NDOT resilient model correlation equation overestimates the resilient modulus anticipated in an existing pavement structure, thus resulting in a likely under designed asphalt concrete layer thickness.
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