Numerical Simulation Study On Water-heat Coupling Mechanism Of Unsaturated Soil

In recent years,with the development and transportation of energy and the rapid application of urban underground space freezing construction methods,more and more projects involve the problem of the effect of water and heat coupling on unsaturated soil structures.Therefore,it is of great practical significance and engineering application value to carry out research on the influence of the temperature of heating and cooling sources on unsaturated soil structure.The main content of this article is based on the previous research,through the improvement and innovation of traditional calculation models,to study the problem of the coupling of water and heat corresponding to different working conditions of unsaturated soils under heating and cooling sources.At the same time,the QSGS method is used to reconstruct the soil model,showing the change law of the soil structure in different situations.Its corresponding research results have important value in scientific research and engineering applicability.The main research contents are as follows:(1)Under the action of heat source,because the traditional model only considers the influence of temperature on moisture,and ignores the influence of moisture on temperature,for this reason,by improving the traditional calculation model,this paper can better consider the water and heat At the same time,the effect of the coupling effect is solved discretely by the lattice Boltzmann method which has been newly developed in recent years.Based on this,the evolution of the temperature and moisture fields and the sensitivity of related parameters under different coupling models,different heat source temperatures,and different initial porosities are discussed.The results show that the traditional calculation model has obvious errors in the temperature and moisture fields in the treatment of water and heat coupling.The model proposed in this paper considering the synergistic effect of the two is more reasonable;at the same time,as the temperature of the heat source rises The higher the porosity is,the faster the temperature transfer process is,and the wider the range of its influence is.In addition,under the influence of heat sources,the moisture field tends to gradually increase and then gradually decrease,and tend to be gentle.As the temperature of the heat source increases,the phenomenon becomes more obvious,but its change trend is less affected by the porosity.(2)Under the influence of cold source,the classic Halan model has the characteristics ofstrong coupling and high nonlinearity in the process of solving temperature and moisture distribution,and it is easy to have problems of numerical oscillation and non-convergence of parameters.In order to better solve this problem,this paper proposes a new calculation model based on previous studies,and proves the accuracy of this model through related verification.Based on this,the related issues were discussed in several aspects such as different time,different initial volume water content,different cold source temperature and the influence of impedance factor.It was found that as the cold source temperature decreases,the initial volume contains As the amount of water increases,the deeper the temperature evolution process,the wider the influence range and the further the position of the frozen cover.For the water field,under different circumstances,the water in the unfrozen area will obviously migrate to the frozen area,and at the same time,The accumulation of water gradually occurs at the frontal position with the passage of time,and as the freezing time becomes longer,the temperature of the cold source is higher,and the initial volumetric water content is greater,the phenomenon of moisture accumulation in the freezing area becomes more obvious;In addition,since the influence process of the impedance factor shows different effects with different freezing time and water accumulation effects,it should be considered in time according to the corresponding situation.(3)Through the discussion of the meaning of each parameter in the QSGS method,the calculation efficiency and the relative error of the model,the concept of fit interval is proposed,and on this basis,the soil model is microscopically reconstructed,which affects the heat source and cold source respectively,corresponding The changes of the soil structure under different working conditions are discussed and analyzed.It is found that under the action of the heat source,the pores at the location of the heat source increase and the position slightly away from the heat source appears smaller,and as the temperature of the heat source increases The higher the initial water content,the greater the change in the corresponding internal structure of the soil and the wider the range of influence;under the influence of the cold source,the pores in the frozen area will appear smaller than the unfrozen area,and the freezing The longer the time,the higher the temperature of the cold source,the greater the initial volume of water content,the more obvious the phenomenon,and the more dense the soil structure in the frozen area.