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Many agencies still use empirical correlations developed to determine design subgrade resilient modulus based on California Bearing Ratio (CBR), R-Value or Soil Support Value (SSV) for pavement design projects. These relationships do not consider the stress dependency of the laboratory determined resilient modulus value. Backcalculated subgrade modulus values from Falling Weight Deflectometer (FWD) tests are also used for this purpose. This study was conducted to determine the relationships between laboratory determined subgrade resilient modulus and the results of Lime Rock Bearing Ratio (LBR) and FWD tests for certain Florida subgrade soils. Laboratory resilient modulus values were determined using subgrade soil samples collected from nine pavement sections. The resilient modulus values were computed by considering stress levels under a standard dual wheel in three typical pavement sections. The roadway sections were selected from various locations in Polk County, Florida. FWD tests were conducted along the selected roadways and LBR tests were conducted on bulk subgrade soil samples. Preliminary relationships to determine design subgrade resilient modulus equivalent to AASHTO Road Test subgrade from FWD and LBR tests were developed for considered typical pavement sections.
resilient modulus, california bearing ratio, backcalculation
Pavement Engineer, Dynatest Consulting Inc., Starke, FL
President, Abatech, Inc., Doylestown, PA