Study On The Liquid Nitrogen Freezing Temperature Field In Saline Soil

Artificial ground freezing(AGF) is widely used in mine construction, foundation construction, underground tunnels, hydraulic engineering, but the fracture of freezing pipe has always been a difficult problem in vertical shaft mine construction, called as "cancer" in the AGF, seriously affected the stability of the Frozen Curtain and security. In the case of brine leakage, the freezing point of frozen soil had been depressed. Using liquid nitrogen freezing method, we can pass salt formation quickly to ensure construction safety. This paper is primarily research on the temperature field distribution by using liquid nitrogen as freezing way. It has a great significance and important reference value for the similar projects and to safety in construction.First of all, this paper conducted formation properties of saline frozen soil. The paper mainly determines the frozen soil freezing temperature of different salt content and thermal conductivity etc, also determine the unconfined compressive strength of different salt content and elastic modulus. Then summarizes the rules of the parameters under different salinity, and for subsequent theoretical derivation and numerical simulation provides the necessary parameters.Secondly, this paper conducted the research on the theory of the temperature field. At present, commonly used freezing temperature field formulas don’t consider the freezing temperature is below 0℃. This paper considers the effect of freezing temperature on temperature field. Combined with Japanese formula for two pipe freezing, utilizing the principle of Temperature Superposition, deduced the formula of a single row pipe and double row pipe. After verification, the formula is appropriate for liquid nitrogen freezing in the single row and double row, and meets the engineering accuracy requirements.Furthermore, this paper conducted the physical model test. By simulating of the double row pipe liquid nitrogen freezing, we get the freezing temperature field data, measure the development speed of frozen soil under liquid nitrogen freezing method, This paper also analysis the pipe wall temperature distribution with the length of the liquid nitrogen freezing pipe, and sums up the rule of frozen wall defrost, and compare the similarities and differences with brine freezing temperature field, provides the leaching salt formation of freezing curtain construction suggestions.Finally, a numerical simulation model is established to simulate the accuracy of the physical test model research and theoretical formula. We build a ANSYS model to simulate the liquid nitrogen freezing temperature field, and compared with the theoretical calculation results; build a ANSYS model to simulate the development of the frozen soil and thawing law in by liquid nitrogen freezing, compared with physical model test measurement results. Finally the numerical calculation and theoretical formulas and physical model test results are analyzed, and validates the availability of the numerical simulation model and the applicability of the theoretical formula.