INVESTIGATION OF PHASE CHANGE TEMPERATURE FIELD IN FROZEN SOIL BASED ON ACTIVELY HEATED FIBER OPTICS METHOD

The analysis of frozen soil temperature field plays an important role in the research on frozen soil and engineering construction in permafrost regions. The latent heat caused by the phase change between ice and water increases the complexity of the analysis. In order to solve this problem, the volumetric heat capacity due to phase change and thermal conductivity is obtained through back calculation based on the linear heat source model and the basic theory of heat transfer in frozen soil. In this paper, a series of laboratory tests on frozen soil are conducted for the same initial moisture content. Based on the method of Actively Heated Fiber Optics(AHFO), the FBG corundum tube sensor is used as a heat source and temperature sensor to detect thermal response characteristics of frozen soil under different initial temperature. The results show that under the experimental conditions, the influence radius of the FBG corundum tube sensor is less than 5 cm. The temperature increment measured by the FBG corundum tube sensor has a linear relationship with the logarithm of time. With the increase of initial temperature, the measured thermal conductivity of frozen soil has a linear relationship with temperature. The phase change heat capacity tends to be stable when the initial temperature is lower than -6℃, and increases gradually with the increase of temperature from -6℃ to 0℃. When the initial temperature is higher than -5℃, the phase change heat capacity is even greater than the volume heat capacity of the frozen soil itself. These results provide references for the modification of the AHFO-based monitoring method of ice content in frozen soil.