Superpave In-Situ Stress/Strain Investigation, Phase II Volume IV: Mechanistic Analysis and Implementation

The SISSI data were utilized in the Mechanistic-Empirical Pavement Design Guide (MEPDG), and the predicted condition parameters were compared to those measured in the field. Overall, it was found that the MEPDG only made somewhat reasonable predictions for rutting. It is therefore essential to perform local calibration. The SISSI data provide a valuable source of both response and performance data for that purpose. In order to further understand the sources of differences between measured and predicted performance, it is important to evaluate the differences in mechanistic responses. Therefore, independent mechanistic analysis was conducted in order to compare the responses from finite element analysis to those measured from the instrumentation in the field. In order to correct the finite element responses to correspond to field conditions under a variety of environmental and loading conditions, a site-specific procedure was developed to extrapolate the results. Finite element analysis was also utilized to model loading with the falling weight deflectometer. A comparison of the responses from embedded instrumentation devices during the FWD loading was also made. For surface deflections, the average prediction errors were 9 and 12 percent when using backcalculated and laboratory AC moduli, respectively. For the strain and stress responses, the predicted responses consistently exceeded the measured responses, with a prediction error of 30 to 50%. Finally, parametric studies were conducted to examine possible sources of error in the SISSI experiment. The variation of loading pulse with depth was examined and correction procedures were utilized. An additional concern was that the strain gages themselves might alter the pavement structure and affect the overall response. Therefore, detailed finite element analysis was performed to examine the potential magnitude of the strain gage effects. It was found that the strain gages might result in an error of up to about 80% depending upon other conditions. As the Pennsylvania Department of Transportation moves to adopt and implement the MEPDG, these analyses provide a basis for utilizing the SISSI data in its understanding and calibration. The present report is one of four volumes, Volume I: Summary Report; Volume II: Materials Characterization; Volume III: Field Data Collection and Summary; Volume IV: Mechanistic Analysis and Implementation.