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Federal Highway Administration Research and Technology
Coordinating, Developing, and Delivering Highway Transportation Innovations

This report is an archived publication and may contain dated technical, contact, and link information
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Publication Number:  FHWA-HRT-15-036    Date:  December 2015
Publication Number: FHWA-HRT-15-036
Date: December 2015


Long-Term Pavement Performance Program Determination of In-Place Elastic Layer Modulus: Backcalculation Methodology and Procedures

Chapter 7. Conclusions

The automated backcalculation procedure and tools reported in this report were used to determine the elastic layer properties (or Young’s modulus) from deflection basin measurements for all LTPP test sections. This report summarizes the reasons why EVERCALC© and MODCOMP© were selected for the computations and analyses of the deflection data, provides a summary of the results using the linear elastic modulus for selected test sections, and identifies those factors that can have a significant effect on the results. This chapter includes some of the highlights and findings from this study and recommendations for future activities in support of accomplishing the overall LTPP objectives.


Backcalculation of elastic properties is not an exact science and requires user interaction in some cases. However, the process was automated through a series of utility functions and tools to reduce the impact of user interaction, bias, and/or inexperience. Results from this automated procedure provide elastic layer load response properties that are consistent with previous experience and laboratory material studies related to the effect of temperature, stress state, and seasonal effects on the material load-response behavior. The following list highlights some of the important findings from this study:


The results from this study have shown that elastic layer moduli (or load-response properties) can be computed from deflection basins and provide pavement engineers with useful information about the pavement structure and subgrade condition. However, this study only touched on the different ways the backcalculated elastic layer modulus database can be used for improving pavement design and rehabilitation strategies. More detailed analysis can be completed to demonstrate the usefulness of the deflection data and resulting elastic moduli. The following list highlights some specific topics that can be investigated in the future:




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