Study On Thermal Conductivity Model And Influence Of Thermal Parameters Nonlinearity On Temperature Field Of Frozen Soil

Temperature field,moisture field and stress field of frozen soil should be studied thus to guide the construction of artificial freezing method and cold regions engineering,to ensure the safe operation of the project.The determination of temperature field is the basis for the defining of water migration and the stress distribution,therefore,it is of great theoretical significance and engineering value to study the thermal field and the thermal parameters which affecting the temperature field of frozen soil.Based on the theoretical analysis,the geometric model of frozen soil thermal conductivity was established by the ideal particle accumulation model,and the evolution law of the frozen soil thermal conductivity was revealed.On this basis,the theoretical method for determining the frozen soil thermal conductivity was proposed.Meanwhile,the relationship between the frozen soil thermal conductivity and unfrozen water was determined,and a reducing method of thermal parameters for the frozen soil temperature field calculating was proposed based on the unfrozen water content.Also,the nonlinearity of heat equation and thermal parameters for the calculation of frozen soil temperature field were studied,and the influence of the selection of thermal parameters on the calculation of temperature field was revealed.The main research methods and contents are as follows.Based on the closely spaced soil column model established herein,the variation law of thermal conductivity,specific heat and latent heat with negative temperatures were studied.An aggregation model of the frozen core in the center of the spherical particles and the outward expansion of the concentric spheres was established,and the mixed flow calculation method of frozen soil thermal conductivity was proposed from compositions of saturated frozen soil and microscopics such as the composition of saturated frozen soil,the contact between spherical particles.Based on the column geometric model put forward herein,the volume calculation and evolution law ofwater and ice column variation with temperatures were established considering the contents of three phases in the frozen soil change with the temperatures.On this basis,a calculation model of thermal conductivity considering the effect of solid-liquid interface was established,under the view of the coupling characteristics of parallel connection and series connection in the heat transfer process.The impact and sensitivity of thermal parameters on frozen soil temperature field were analyzed,a reducing method of thermal parameters for the calculation of temperature field was put forward based on the unfrozen water content,the influence of release range hypothesis of latent heat on the temperature field evolution of frozen soil was verified,the relationship between the latent heat of frozen soil and the unfrozen water content was discussed,and the essence of latent heat was pointed out as the inner heat source of the soil.Meanwhile,an integral algorithm for frozen soil latent heat in a temperature interval was established by means of area balance,and a theoretical method to convert the latent heat of frozen soil into a nonlinear changing specific heat was proposed.On this basis,the nonlinear problem of frozen soil heat conduction process was discussed from the point of nonlinear thermal parameters and boundary conditions.Through the above researches,the applicability of the two calculation models of frozen soil thermal conductivity were verified,the test method of true specific heat of frozen soil was perfected,and the relationships between thermal conductivity,specific heat,latent heat and unfrozen water content of frozen soil were elucidated.The impacts from different thermal parameters are larger in the initial freezing stage and then the differences among all the calculated values will gradually reduced.The latent heat influences the temperature distribution of frozen soil both in the phase-changing region and the phase-changed region,the final freezing temperature should be fully considered when selecting the thermal parameters in the calculation of frozen soil temperature field.From the view of the inversion of unfrozen water content by frozen soil thermal parameters,it is feasible to reduce the workload of thermal parameters by using the thermal parameter test values.The research set a foundation for the study of frozen soil temperature field prediction,model test similarity criterion and analytic solutions.