1. Analysis of Variations of Pavement Subgrade Soil Water Content 1 Andrew G. Heydinger, Ph.D., P.E. and 2 B.O.A. Davies 1 Professor and 2 Former Graduate Student Department of Civil Engineering The University of Toledo Toledo, Ohio

2. Purpose of Research To analyze the long term pavement performance (LTPP) climatic data in the Federal Highway Administration (FHWA) database, DataPave, for the seasonal variations of pavement subgrade soil volumetric water content. To infer impacts of the seasonal variations of moisture on pavements by considering the effects of subgrade moisture content on subgrade soil resilient modulus.

3. Significance of Research Water content or degree of saturation is used to compute resilient modulus for unsaturated subgrade soils in the Mechanistic-Empirical Pavement Design Guide (M-EPDG) that was developed for the FHWA. Since a mechanistic approach is taken, it is necessary to know the variations of material properties.

4. Resilient Modulus Empirical equation proposed in the M-EPDG. Where a, b,  and k s are material parameters. Values for the parameters are recommended in the M-EDG for coarse and fine-grained soils.

5. Seasonal Monitoring Program (SMP) 63 Sites with Seasonal Instrumentation

6. Four Climatic Regions

7. SMP Instrumentation

8. TDR Moisture Measurements Results of laboratory testing on fine-grained soils by Klemunes (1998).

9. TDR Moisture Measurements Field and laboratory tests on a fine-grained soil (Heydinger and Randolph, 1998).

10. PCC Section in Ohio

11. AC Section in Ohio VWC(t) = 37.1 + 1.66 sin[2π/365.25(t-130)

12. VWC and Precipitation for AC Section

13. WF Sections, Coarse-Grained Soil

14. WF Sections, Fine-Grained Soil

15. WNF Sections, Fine-Grained Soil

16. WF Sections, Coarse-Grained Soil

17. WF Sections, Fine-Grained Soil

18. WNF Sections, Coarse-Grained Soil

19. DNF Sections, Coarse-Grained Soil

20. Summary TDR volumetric water content data from the LTPP database DataPave (Release 19) were analyzed in order to investigate volumetric water content variations in subgrade soils. Variations in resilient moduli were computed as a function of degree of saturation using soils data in DataPave and an empirical equation from the Mechanistic-Empirical Pavement Design Guide (M-EPDG).

21. Conclusions Seasonal variations of volumetric water content were observed in some of the sections, with some sections having insufficient data. The variations between the maximum and minimum volumetric water content are typically 3% or higher and can be as high as 9% so it is concluded that moisture variations do occur in subgrade soils. Using moisture content variations, resilient moduli of subgrade soils vary by as much as a factor of 2 but the variations are typically lower.