Implementation of the MEPDG for flexible pavements in Idaho.
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2012-05-01
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Edition:Final report; 05/01/2009-05/11/2012.
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Abstract:This study was conducted to assist the Idaho Transportation Department (ITD) in the implementation of the Mechanistic-Empirical Pavement Design Guide (MEPDG) for flexible pavements. The main research work in this study focused on establishing a materials, traffic, and climatic database for Idaho MEPDG implementation. A comprehensive database covering all hierarchical input levels required by MEPDG for hot-mix-asphalt (HMA) and binders typically used in Idaho was established. The influence of the binder characterization input level on the accuracy of MEPDG predicted dynamic modulus (E*) was investigated. The prediction accuracy of the NCHRP 1-37A viscosity-based Witczak Model, NCHRP 1-40D-binder shear modulus (G*) based Witczak model, Hirsch model, and Gyratory Stability (GS) based Idaho model was also investigated. MEPDG Levels 2 and 3 inputs for Idaho unbound materials and subgrade soils were developed. For Level 2 subgrade material characterization, 2 models were developed. First, a simple R-value regression model as a function of the soil plasticity index and percent passing No. 200 sieve was developed based on a historical database of R-values at ITD. Second, a resilient modulus (Mr) predictive model based on the estimated R-value of the soil and laboratory measured Mr values, collected from literature, was developed. For Level 3 unbound granular materials and subgrade soils, typical default average values and ranges for R-value, plasticity index (PI), and liquid limit (LL) were developed using ITD historical data. For MEPDG traffic characterization, classification and weight data from 25 weigh-in-motion (WIM) sites in Idaho were analyzed. Site-specific (Level 1) axle load spectra (ALS), traffic adjustment factors, and number of axles per truck class were established. Statewide and regional ALS factors were also developed. The impact of the traffic input level on MEPDG predicted performance was studied. Sensitivity of MEPDG predicted performance in terms of cracking, rutting, and smoothness to key input parameters was conducted as part of this study. MEPDG recommended design reliability levels and criteria were also investigated. Finally, a plan for local calibration and validation of MEPDG distress/smoothness prediction models for Idaho conditions was established.
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