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Primary Topic: Pavement Testing
Description: Time domain reflectometry (TDR) has become one of the most reliable methods for measuring in-situ soil moisture content. TDR sensors developed by the Federal Highway Administration (FHWA) are being used in the Long-Term Pavement Performance (LTPP) Seasonal Monitoring Program (SMP) to monitor the in-situ moisture content at selected LTPP sites. The main goal of the study reported here was to develop procedures to produce good estimates of in-situ gravimetric moisture content. All the TDR traces in the LTPP database were processed using the approach described in this report.
To estimate the in-situ gravimetric moisture content, methods were selected to interpret TDR traces. An algorithm and a computer program, Moisture, were developed to implement these TDR interpretive methods. After that, the apparent length of the TDR trace and the dielectric constant of the unbound material were computed. Models were developed to relate dielectric constant with in-situ volumetric moisture content. Finally, gravimetric moisture content was computed using the volumetric moisture content value and dry density of the soil. A diagnostic study of the computed gravimetric moisture content was also conducted to evaluate the reasonableness of the computed moisture contents.
As part of the overall LTPP data analysis effort, it is expected that the information on the seasonal variation in the moisture content of the unbound base, subbase, and subgrade layers will be used to develop improved understanding of the seasonal variation in the load-carrying capacity of pavements and the subsequent effect on pavement performance.
FHWA Publication Number: FHWA-RD-99-115
Publication Year: 1999
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