Experiments,Models And Mechanism Studies On Unfrozen Water Hysteresis Effect In Freezing And Melting Process Of Soils

The Soil plays an important role in modern projects.In the natural environment,soils may go through freezing and melting when surrounding temperature is relatively low.Processes of freezing and melting also bring changes to unfrozen water content,which also greatly influence mechanical and thermal properties of soils.As a special kind of porous media,rules and conclusions studied in soils can also be utilized in other porous media.Therefore,relevant studies on unfrozen water content in soils are very valuable and also practical in various engineering applications.Firstly,we give analytical solutions for the influence of unfrozen water on heat transfer in soils,and improve the existed solution process,which is proving the existence and uniqueness of a series of parameters which describing movements of isotherms.Also,we provide the calculation process of these parameters.It is proved that unfrozen water content influences development of temperature filed and movement of frozen front a lot.Afterwards,a test system of unfrozen water based on NMR technique is utilized to acquire unfrozen water content during processes of freezing and melting.With data collected during these processes,soil freezing and melting curves are drew to preliminarily analyze change rules of unfrozen water.In the series of experiments,we mainly studied impacts of temperature path and primary water content on hysteresis effect of unfrozen water in soils.Results of experiments shows that soils with higher primary water content also possess higher hysteresis degress,the same as soils go through larger temperature area.In addition,we build similarity theories between unfrozen water in frozen soils and liquid water in unsatured soils.Five theoretical models,founded by former scholars,which can predict wetting curve by drying one of soil,are introduced to predict melting curves by the frozen.Using data existed in past research and our new NMR experiments,we make comparison among predicted results of different models.After that,three of them are pick out and used for future application.At the end of this paper,we summarize existed mechanisms of hysteresis effect about unfrozen water,present corresponding theoretical formula,and form a theory frame of hysteresis effect analysis.Firstly,pore distribution probability function can be obtained by comparing boundary frozen curves with testing data;In addition,distribution function of freezing melting difference factor can be obtained by comparing boundary melting curves with testing data.Sub-freezing and melting curves can be predicted with these two functions,and further experiments are needed for relative verification.