Study of thermal conductivity model of frozen soil skeleton

In order to study the relationship among soil, water and ice in the thermal conductivity of soil during freezing, we establish the thermal conductivity calculation model based on frozen soil skeleton. The skeleton model consists of the soil skeleton and the ice skeleton, as well as the relationship among the three phases of soil, water and ice. When the temperature decreases to the initial freezing temperature, the pore water far away from the soil particles freezes into ice nuclei first. With the decrease of temperature, the ice core gradually expands to form a perforated pore ice skeleton. The unfrozen water in the frozen soil exists between the soil skeleton and the ice skeleton. According to the ideal model of spherical contact, we put forward the hybrid heat transfer mode which is composed of soil skeleton and ice skeleton, which are independent of each other, soil skeleton mixed with unfrozen water and ice skeleton mixed with unfrozen water. We also establish the three-phase composite heat transfer model of soil, water and ice based on saturated frozen soil and the thermal conductivity model of frozen soil. According to the model, we can obtain the thermal conductivity of frozen soil below 0 ℃. Compared with the calculated values of Johansen method and the mixed flow method, the results of transient method show that the calculated value of composite heat transfer method is larger than the measured value in the range of -5~0 ℃, the reason is that the pore ice skeleton is not mature. When the temperature is below -5 ℃, the calculated value of the composite heat transfer method is larger than the measured value, which is due to the hydrothermal migration in the frozen soil. The calculated values of the composite heat transfer method are between those of the Johansen method and those of the mixed flow method. The overall calculation accuracy is better than that of the Johansen method, and the relative difference between the calculated values and the measured values is less than 10%.