Seasonal Variation of Subgrade Modulus in Different Subgrade Soils for Pavement Rehabilitation for Non Freeze-Thaw Climates

Subgrade soil modulus is a required parameter for the AASHTO method of flexible pavement design and an indirect input parameter for rigid pavement design. Falling Weight Deflectometer (FWD) testing often performed to determine the insitu subgrade modulus of in-service pavement structures for pavement rehabilitation. Seasonal variations of subgrade modulus often complicate the pavement design process and hence the 1993 AASHTO flexible pavement design guide introduced an effective subgrade modulus concept to estimate the effect of seasonal variation of subgrade modulus on pavement performance. This study was conducted to determine the seasonal variation of subgrade modulus values with three types of subgrade soils; clayey sand, silty sand and poorly graded sand. Long Term Pavement Performance (LTPP) program under the Strategic Highway Research Program (SHRP) provides a substantial data source to evaluate the seasonal variation of subgrade modulus values. FWD deflection data were back calculated using DAPS back calculation program and evaluated with different subgrade soil types. This evaluation provides a better insight for future research to estimate an effective subgrade modulus ratio for different subgrade soil types.