Developing Correlation Relationship between Modulus of Subgrade Reaction and Resilient Modulus for Florida Subgrade Soils

The resilient modulus of pavement subgrade is an essential parameter for mechanistically based pavement design procedures; the modulus of subgrade reaction (k) is used as a primary parameter for rigid pavement design. The AASHTO pavement design guide (1986, 1993) suggested a theoretical relationship between modulus of subgrade reaction and resilient modulus of subgrade based on the assumption that the subgrade material is linear elastic. This paper presents an experimental study to evaluate the load–deformation and resilient modulus characteristics of the granular subgrade soils with the use of field and laboratory tests. An extensive field static plate bearing load testing program was conducted to evaluate the in situ bearing characteristics of typical Florida pavement subgrade soils. A full-scale laboratory evaluation of the subgrade performance was conducted in a test-pit facility that simulated the actual field conditions. A laboratory triaxial test was performed to evaluate the resilient modulus characteristics of the subgrade materials. Comparative studies were conducted to evaluate the resilient modulus from laboratory triaxial tests and field experimental studies. Correlation relationships were developed between the measured resilient modulus in the laboratory and the resilient modulus measured with the use of a test-pit facility and between the subgrade soil resilient modulus and the modulus of subgrade reaction. The calibrated relationship based on the experimental studies was close to the AASHTO theoretical relationship. The calibrated relationship could be used in the Florida pavement design guide to obtain realistic subgrade resilient modulus values from laboratory resilient modulus measurements.