Experimental And Simulation Of Soil Moisture Evaporation Process

In recent years,due to the global climate,the frequent occurrence of droughts has had a serious impact on human production and life.Evaporation is one of the main processes of drought disaster,under the occurrence of the extreme arid climate,water evaporation seriously affects the engineering properties of the soil.In this paper,based on the National Natural Science Foundation of China(41572246),a series of indoor research work has been carried out from the study of soil evaporation process,including the soil evaporation experiment combined with Electrical Resistivity Tomography(ERT)technology and evaporation experiment of soil pans that studies the factors of soil influence,and also carried out the numerical simulation of soil evaporation process.From the indoor experiment to the combination of computer simulation,through a number of new technologies and methods to carry out a comprehensive study of soil evaporation,the main work and the results are summarized as follows:(1)The law of moisture content change in the process of soil evaporation was studied by indoor model test.TDR was used to monitor the moisture content of the soil during the evaporation process.The results show that the evaporation of the soil starts from the surface soil,and the evaporation surface gradually moves downwards,and the moving speed becomes slow with the increase of the depth.The water content in the surface soil is rapidly evaporated in a short time,and the evaporation rate decreases with time.The deep soil is saturated in the whole evaporation process,and no water is reduced.In addition,the farther away from the surface of the soil,the greater resistance of the upward movement of water to overcome,showing a higher residual moisture content.(2)Based on the ERT technique,the change of the apparent resistivity of the soil evaporation process was studied,and the quantitative relationship between the apparent resistivity and the water content was constructed.Through the ERT technique,the change of the resistivity of the soil during the evaporation process is measured.At the same time,compared with the water content data,it is found that the higher the water content of the soil,the lower the apparent resistivity.And the water content of the soil decreases with the evaporation,as the resistivity will gradually increase.Therefore,the relationship between the apparent resistivity and the corresponding water content is established.Based on this,the monitoring and evaluation of soil water field in the process of evaporation are established by ERT technology.At the same time,the reliability of ERT technology is evaluated by using the date of the soil water content sensor.The results show that this technique can reflect the evolution of soil water field lossless,real time and truthful.(3)The numerical simulation of soil evaporation process was carried out,based on the unsaturated soil water-heat coupling model.The numerical simulation of soil evaporation process was carried out by FreeFem++software,and the variation of soil parameters was obtained.The simulation results show that the evaporation of the soil starts from the surface,and the evaporation surface moves downwards.Some of the soil water above the evaporation surface is continuously lost,and the water in the soil below the evaporation surface is not reduced.In the end,the evaporation surface moves slowly,and the evaporation of the whole soil becomes weak,the soil surface forms a certain thickness of the dry layer,effectively hinder the evaporation.(4)Numerical simulation results is compared with the indoor model experiment results to verify the numerical model.The numerical simulation results are in good agreement with the results obtained in the experiment.Evaporation starts from the surface,and the evaporation surface gradually moves downwards.The evaporation of deeper soil begins later,and the final evaporation surface is difficult to continue moving down.The soil below the evaporation surface is still saturated.However,there are some differences between the numerical simulation results and the experimental results.At the beginning of evaporation,the simulated water content of the profile shows that the up soil is slightly lower than that of deep soil,while the water content profile at the beginning of the experiment shows a uniform pattern.(5)The influence of soil properties on soil evaporation was systematically studied.A series of laboratory experiments were carried out to study the effects of soil thickness,sand content and sand particle size on soil evaporation process.The results show that the effect of soil thickness on the evaporation is mainly in the constant rate stage.Greater thickness of the soil leads to stronger evaporation.Soil sand content affects the whole process of evaporation.Soil has larger sand content would have higher the evaporation rate.And the effect of soil particle size on the evaporation is mainly in the falling rate stage.The higher the particle size is,the higher the evaporation rate will be.