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 (EICMF_env) curve for seasonal subgradeM_Rchanges. 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-99M_Rtest method was used on all samples with an additional eight specimens being tested with NCHRP 1–28AM_Rtest method. Four soils from Louisiana which were not from the six roadways were also tested and included in the analyses. Once theM_Rtests were completed and plotted, it was noticed that there was a rather large scatter (R² = −0.266) around the EICMF_envcurve. 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 EICMF_envmethod to determine the relationship between changes in subgradeM_Ras a function of changes in moisture content with the in situ moisture content andM_Rused as the control. This method differs from the EICMF_envin that the EICMF_envuses 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.

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