Application of time domain reflectometry method in monitoring state parameters of subgrade soil in pavement

Moisture content has a direct influence on structural performance of pavement. Every year in Australia, heavy vehicles damage roads when the moisture content of the pavement layers reaches a critical value because of heavy rainfall or flooding. When the moisture content changes, increased moisture contents often lead to premature pavement damage under cyclic loading. Time domain reflectometry (TDR) is a noninvasive technique for measuring moisture content. The existing and newly developed TDR sensors are calibrated in the laboratory with materials of subgrade layer from the pavement. These calibrated sensors are installed in both the shoulder and wheel paths of a newly constructed pavement to monitor the dielectric characteristics of the materials. The dielectric characteristics are further utilized to calibrate in situ moisture of the pavement materials as well as transverse moisture distribution across the pavement. Moreover, the electrical conductivity and density of the materials are estimated based on the information of dielectric properties. Finally, the state parameters, namely moisture content, electrical conductivity, and density are obtained from the road instrumentation that would improve the pavement management in terms of damage, like surface deformation or rutting