Hydro-Thermal-Mechanical Coupled Model Research Of Freezing Soils On Pre-melting Theory

The area of frozen soil in China is widely distributed.There are so many engineering hazards associated with frost heave in cold regions and development of underground space using artificial freezing methods.The essence of solving these problems is to understand the hydro-thermalmechanical coupled characteristics caused by soil freezing and thawing.In response to this problem,many scholars at home and abroad have conducted a lot of research,however,due to the complexity of the problem,the description of the physical evolution regular during the freezing process is still not clear enough.The pre-melting theory explains the frost heave mechanism from the microscopic level,but the theory can’t consider complex temperature filed and stress temporarily.Based on the pre-melting theory and the study of the temperature field of frozen soil,the hydrothermal coupling model of frozen soil is established by introducing the energy equation into the pre-melting theory,and the hydro-thermal-mechanical coupling model of frozen soil is established on the basis of the effective stress principle.The model solves the problems that the physical state of the previous model is not clear and the pre-melting theory cannot dynamically describe the soil temperature field.The reliability of the two models was verified by laboratory tests.Simultaneously,the parameter sensitivity analysis of frost heave and initial frost shrinkage was performed.The specific research contents are as follows:(1)The principles and model equations of the pre-melting theory were systematically summarized,and the influence of overburden and porosity on the growth and initiation of lens were discussed.By assuming the frost heave rate and the freeze rate,the regularity of the lens location and thickness under different freezing rates and heave rates are obtained.Simultaneously,the microscopic mechanism of ice lens formation and evolution is revealed.(2)Starting from the process of nucleation and crystal growth,the basic physical process of phase transition was analyzed,and the energy equation was established by introducing the evolution equation of ice content to express the freezing rate and final fraction of ice.Aiming at the one-dimensional and two-dimensional freezing problems of soil,a calculation model is established to analyze the influence of phase transition on the transient temperature field of frozen soil,and the distribution law of temperature field of frozen soil under the influence of phase transition is obtained.(3)Based on the theory of pre-melting frost heave model,the model coupled heat and moisture transfer in soil freezing was established by combining with the transient temperature field equation with phase transition.The accuracy of the model were in general agreements with experimental results from Konrad’s tests,and the effects of overburden,cooling type,cooling rate,and soil types on frost heave were analyzed.(4)Considering the influence of the stress field on the basis of the hydrothermal coupling model,a hydro-thermal-mechanical coupling model was established based on the principle of effective stress.Subsequently,the finite element equation discretized in space and time domain of the governing equations were derived in detail.The correctness of the model and the reliability of the calculation method were verified by Hu Kun’s tests.The main factors affecting the soil frost heave and initial frost shrinkage were systematically analyzed.