The computer program known as CalME was developed as part of the California Department of Transportation’s (Caltrans’) endeavor at adopting Mechanistic-Empirical (ME) methods of pavement design. CalME has three levels of flexible pavement design; for new pavements as well as for rehabilitation. Level one is the existing empirical methods presently used by Caltrans. Level two is a “classical” ME approach, largely based on the Asphalt Institute’s method, and level three is an incremental-recursive approach which allows Caltrans to validate and/or calibrate different mechanistic and empirical models.

The models of CalME have been calibrated using Heavy Vehicle Simulator (HVS) tests on new pavements as well as on overlaid pavements. This paper describes the validation and calibration done using the Federal Highway Administration’s (FHWA’s) project commonly referred to as WesTrack. WesTrack was subjected to frequent Falling Weight Deflectometer (FWD) testing and rutting, roughness and distresses were also recorded. Additionally, frequency sweep and resilient modulus tests were done on the asphalt materials, used in constructing WesTrack pavements, to characterize the master curves, and fatigue tests and shear tests were also conducted to determine the constants of the fatigue damage and permanent deformation models. Similarly, triaxial tests were done on the unbound materials.

For each of the 26 original sections the results of the WesTrack experiment were imported to the CalME database, and the experiment was simulated, hour by hour, using the incremental-recursive method with the model parameters derived from laboratory tests.
The measured FWD deflections were compared to the deflections calculated by CalME, to ensure that the pavement response was predicted reasonably well, for the duration of the experiment. The empirical parts of the ME models were then calibrated, so that the predicted performance would closely match the measured performance.

For prediction of asphalt fatigue a shift factor between laboratory fatigue and in-situ fatigue was determined, ranging from 5 to 15 depending on the type of asphalt mix. For permanent deformation of the asphalt layers the permanent strain determined from Repeated Simple Shear Tests – Constant Height (RSST-CH) in the laboratory should be multiplied by a factor of 80 to 90, depending on the mix type, to result in the measured permanent deformation of the asphalt, in mm. The models used for unbound materials in the HVS experiments were confirmed.