LTPP Computed Parameter: Moisture Content
Primary Topic: Pavement Data Collection
Description: A study was conducted to compute in situ soil parameters based on time domain reflectometry (TDR) traces obtained from Long Term Pavement Performance (LTPP) test sections instrumented for the seasonal monitoring program (SMP). Ten TDR sensors were installed in the base and subgrade layers at each of the 70 SMP test sites monitored as part of the LTPP program. A comprehensive description of a new method developed as part of the study to estimate moisture content, dry density, reflectivity, and conductivity of the soil from TDR traces is provided in the report. This new method utilizes transmission line equations and micromechanics models calibrated to site-specific conditions for each site/layer combination. Background information on existing empirical methodologies used to estimate subsurface moisture content from TDR traces is also documented. The results were compared to previous methods as well as ground truth data to evaluate the ability of the new model to predict soil parameters. The transmission line equation and micromechanics method was found to provide accurate results and was used to interpret over 270,000 TDR records stored in the LTPP database. A computer program (MicroMoist) was developed to aid in the computation of soil parameters based on TDR trace data and calibration information. Details on the program are provided along with descriptions of the tables developed to store the computed values in the LTPP Information Management System database.
FHWA Publication Number: FHWA-HRT-08-035
Publication Year: 2008