| China's seasonal frozen soil area covers a wide range,and periodic freezing and thawing is the main factor causing water migration.Freeze-thaw diseases are closely related to soil temperature changes and water migration.Both frozen soil temperature changes and water migration will affect each other.In this paper,based on the ground freeze-thaw deformation monitoring of the photovoltaic project site in Kangping County,Shenyang,an indoor freeze-thaw test was conducted on the silty clay in the site under water replenishment conditions,and the temperature conditions,initial moisture content,and freeze-thaw cycles were analyzed The law of influence on water and heat migration of silty clay based on the theory of unsaturated soil seepage and heat conduction,a water-heat coupling model of frozen soil was established.Using the data of the indoor freeze-thaw test for analysis,the law of the volume content of the unfrozen water in the freezing and thawing phases with temperature is obtained,and the relationship between the volume content of the unfrozen water and the temperature is fitted to obtain the freezing process and the melting process coefficients a,b of the relationship between the volume content of unfrozen water and temperature;the PDE interface of COMSOL Multi-physics software was used for secondary development,and the temperature field and moisture of frozen soil were developed the numerical simulation of the field verifies the effectiveness of the hydrothermal coupling model.A three-dimensional numerical model of freezing and thawing on the site was established,and the deformation law of the site under the action of freezing and thawing cycle was analyzed.Through the above research,the following conclusions are obtained.(1)During the freeze-thaw process,there are temperature-affected zones and nontemperature-affected zones in the sample.The range of temperature change in the temperatureaffected zone is large,and the range of temperature change in the non-temperature-affected zone is small.The rate of heat absorption by the soil in the non-temperature affected area is basically the same as the rate of heat release,so the temperature of the soil layer near the bottom of the sample is relatively stable.(2)The volume content of unfrozen water at each point of the sample centerline is positively correlated with the freezing temperature.Under the same initial moisture content,the higher the freezing temperature,the higher the volume content of unfrozen water;the number of freeze-thaw cycles The effect of volume content will gradually weaken over time.(3)During the freeze-thaw cycle,under the same temperature conditions,the higher the initial moisture content,the greater the frost heave rate and thawing coefficient.(4)Fitting the relationship between the volume content of unfrozen water and the temperature to obtain the coefficients a and b in the phase transition dynamic equilibrium equation.Take a = 44.11 and b =-0.58 during the freezing process;and a = 43.78 during the thawing process.b =-0.52.(5)The changes of temperature field,moisture field and displacement field under model test conditions and numerical simulation conditions are compared to verify the reliability of the model.(6)It can be seen from the calculation results of the freezing and thawing of the site that the frost heaving started from the end of October in the whole cooling process and reached its maximum in March.Due to the increase in temperature in April,the ground has experienced significant thawing.The frost heaving and thawing conditions in the southern and eastern regions of photovoltaic power plants are more severe,while the northern and western regions are relatively mild.Comparing the numerical calculation results with the in SAR satellite monitoring data,it can be found that the changes of the two are basically the same.Therefore,it can be considered that this calculation method is feasible to predict the site deformation of the project.This paper has 57 pictures,13 tables and 91 references. |
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