Modeling the Resilient Modulus Variation of in Situ Soils due to Seasonal Moisture Content Variations

LTRC is conducting a research project to determine the seasonal variation of subgrade resilient modulus (M _R ) in an effort to implement PavementME. One objective of that project, which is presented in this paper, was to locally calibrate the Enhanced Integrated Climate Model's (EICM F _env ) curve for seasonal subgrade M _R changes. Shelby tube sampling was conducted on six different roadways to a depth of approximately 7.92 m beneath the shoulder pavement's base course. The AASHTO T-99 M _R test method was used on all samples with an additional eight specimens being tested with NCHRP 1-28A M _R test method. Four soils from Louisiana which were not from the six roadways were also tested and included in the analyses. Once the M _R tests were completed and plotted, it was noticed that there was a rather large scatter (R ² = -0.266) around the EICM F _env curve. The authors hypothesized that this occurred due to the density differences between in situ and remolded specimens. Further analyses confirmed this hypothesis. LTRC developed a new method based on the EICM F _env method to determine the relationship between changes in subgrade M _R as a function of changes in moisture content with the in situ moisture content and M _R used as the control. This method differs from the EICM F _env in that the EICM F _env uses optimum moisture content as the controlling parameter. The LTRC method can be used for design purposes as well as level 2 inputs into the EICM.