Applicability of Optical Fibers for Monitoring the Temperature and Moisture of Freeze-Thaw Soil

Abstract

Abstract Real-time measurements of soil temperature and moisture fields in freeze-thaw areas provide data support for improving the durability of infrastructure. Compared to traditional sensors, optical fibers can determine soil temperature and moisture fields accurately, efficiently, and reliably, but their monitoring characteristics in freeze-thaw areas must be further investigated. In this study, optical fibers are applied for monitoring soil temperature and moisture in freeze-thaw soil based on distributed temperature sensing and an actively heated fiber optic method. The test results indicate that the spatial resolution of a fiber measuring tube constructed by winding optical fibers is 34 times higher than single fibers. A high correlation is confirmed between data measured by optical fibers and traditional sensors. For the soil temperature, the coefficient of determination is 0.98 and the root mean square error is 0.90°C. For the soil volumetric water content, the coefficient of determination is 0.94 and the root mean square error is 2.17 %. Furthermore, the optical fibers can identify the boundary between frozen and unfrozen soil through the value measured in the freeze-thaw process. The results reveal that the optical fibers are efficient in monitoring soil temperature and moisture fields in the freeze-thaw process and carry the advantages of in situ and distributed measurements, high measuring precision, and wide adaptability in working conditions.