Time Domain Reflectometry for Indirect Measurement Change During Freeze-Thaw Process of Soil Volume

The variation of soil mechanical properties during the freeze-thaw cycles, especially the reduction of air suction in the thaw stages, was investigated in this paper. The reduction of air suction is the major cause of the volume expansion between 20–50 min during the thaw stage. An innovative TDR tube sensor was developed to nondestructively monitor the freeze-thaw process, from which the water content and the degree of freeze-thaw can be accurately determined. Compared with existing technologies for frost measurement, TDR has advantages in that it provides more details on the progresses of freeze-thaw status. With the assistance of this tool, not only the onset of freeze or thaw process, but also the extents of their development can be investigated. From the measured soil mechanical properties, an analysis is given to calculate the change of air suction during the thaw stage. The air suction at complete thaw status can be measured by use of a traditional instrument, such as a tensiometer. As a result, the air suction pressure during the thaw process can be indirectly measured.