Methodology to Improve the AASHTO Subgrade Resilient Modulus Equation for Network-Level Use: Fid-Bau Portal

Methodology to Improve the AASHTO Subgrade Resilient Modulus Equation for Network-Level Use

Boo Hyun Nam

Falling weight deflectometer (FWD) testing is commonly used to estimate subgrade resilient modulus (M...) by using back calculation and/or the AASHTO M... equation. Considering the availability of limited information in the pavement management information system (PMIS) database, the AASHTO M... approach is suitable for subgrade assessment at a network level because of its simplicity. An adjustment factor is commonly applied to the AASHTO M... equation because of the difference between laboratory-measured M... and estimated M... However, large variations in the adjustment factor have been observed with different geographical locations and climate conditions. Thus, using a fixed value of the adjustment factor has led to inaccurate assessment of subgrade soil M... This paper presents a methodology to improve the accuracy of the existing AASHTO M... equation by constructing an M... adjustment factor based on the correlation of back-calculated E... and AASHTO M... This study also investigated the effects of subgrade soil stiffness, bedrock depth, highway classification, and environmental condition on the correlation. Additionally, the uncertainty of the AASHTO subgrade M... equation because of the variation in the adjustment factor was quantified. As an example analysis, the methodology was applied to five districts in the state of Texas. The newly constructed M... could reduce variation in the adjustment factor, increasing the R... value from 0.524 to 0.894 in the correlation. The developed methodology can be applied to a smaller set of FWD data such as each road and county, which can reduce an uncertainty in the adjustment factor. (ProQuest: ... denotes formulae/symbols omitted.)