The ability to accurately monitor subsurface soil parameters on a continuous basis is extremely beneficial in pavement design, evaluation, and  performance prediction. The time domain reflectometry (TDR) data collected as part of the Long Term Pavement Performance seasonal monitoring program (SMP) can be used to estimate moisture content, conductivity, reflectivity, and density. This report provides valuable information on calculating these parameters utilizing TDR traces and documents the process of interpreting over 270,000 TDR traces taken at SMP sites across North America.


In situ data availability is critical to pavement engineering, particularly as the process moves toward mechanistic-empirical techniques. This study not only provides useful information from in-service pavements, but also provides a method that can be utilized by State highway agencies interested in monitoring subsurface conditions and analyzing their effect on pavement response.