Research On Construction And Simulation Analysis Of Unsaturated Soil Thermal Conductivity Model In Alpine Region

With the rapid development of economy and the continuous increase of population,the scope and intensity of human production and living have continued to increase,and problems such as energy shortages,environmental degradation,soil desertification and water pollution have emerged.For alpine regions,the warming and degradation of the soil layer has caused catastrophic problems such as subsidence,cracking,and deformation of buildings,roads,and pipelines built on the area,which need to be urgently addressed.The thermal parameters that affect the change of heat and mass transfer characteristics of unsaturated soils in the alpine region mainly include thermal conductivity,specific heat and latent heat.For the change of thermal conductivity of unsaturated soil,the soil composition structure and the material phase state in the pores have influences on it.Especially in the freezing and thawing process in winter,the phase state,composition and distribution of soil change greatly,and the thermal conductivity changes greatly.At present,there are some deficiencies in relevant researches.This paper presents the selection method of Representative Elementary Volume(REV)for ice-containing unsaturated soil with porosity as the representative state variable.Considering the freezing and thawing conditions,two REV analysis models of ice-containing unsaturated soil are established: Simplified volume weighted REV model(Simplified series model and Simplified parallel model)and Detailed volume weighted REV model.The macroscopic thermal conductivity analysis model(Comprehensive series-parallel model and Comprehensive parallel-series model)is given.The formulas for calculating the thermal conductivity of each model are derived.The experimental values and the calculated values of the Detailed volume weighted REV model were compared with the specification values.The results show that the calculated value of the Detailed volume weighted REV model has a maximum deviation of +13.4% and a minimum deviation of +0.594% compared with the specification value;the experimental value has a maximum deviation of +20.3% and a minimum deviation of +0.594% compared with the specification value.The deviation of the calculated value from the specification value is smaller than that of the experimental value from the specification value.Therefore,the model established in this paper is practical.Taking cold area soil sand as an example,numerical calculation was performed under the conditions of standard atmospheric pressure of 101.325 k Pa and temperature of 0?.The variation characteristics of thermal conductivity and related parameters(porosity,water content,ice content and tortuosity)of frozen soil are discussed.The results show that the thermal conductivity increases with the increase of water content,ice content and tortuosity;the thermal conductivity decreases with the increase of porosity and pore channel distribution coefficient.The model established in this paper improves and develops the analysis of thermal conductivity characteristics of unsaturated soil.