Automation of Pavement Sublayer Moisture Content Determination Using Long-Term Pavement Performance Time Domain Reflectometry Data and Micromechanics

Abstract

Time domain reflectometry (TDR) is one of the reliable methods to measure in situ moisture content of unbound base and subgrade materials. However, the waveform data obtained from the TDR device do not provide in situ moisture content directly. Rather, the data must be analyzed to determine volumetric moisture content, which is the final product of TDR-related technology; that is, a TDR trace is analyzed to determine the value of the associated dielectric constant, which depends on the soil surrounding the TDR probe affecting the moisture content determination. However, because existing methods to determine the dielectric constant and moisture content are immersed in systematic errors, a new approach was developed; it used the transmission line equation and a three-phase micromechanics approach to improve the accuracy of the interpretation of TDR data for calculating the dielectric constant and the moisture content. Because the system identification method used to calculate parameters in the new approach was an iterative solution scheme, a computational program was required to provide rapid, accurate, and repeatable calculation of parameters. To address this need, a program was developed to facilitate the calculation of dielectric constant, dry density, and moisture content using the micromechanics approach. Details regarding the feature, algorithm, and results of the program are provided.