Modeling and verification of freezing temperature for sodium sulfate saline soil
Saline soils are widely distributed in the cold and arid regions of northwestern China.The freezing temperature of soil is a critical temperature at which the physical properties of soil undergo significant changes.This temperature determines whether the soil is in a frozen state or not,and it has an effect on frost heave defor-mation.Additionally,the freezing temperature is a crucial parameter in calculating the freezing depth and is closely associated with the formation of segregated ice and the migration of water and salt in the soil.But due to the presence of salt,predicting the freezing temperature is challenging in saline soils,and consequently,accu-rately predicting the freezing temperature of saline soil is of significant importance for engineering damage treat-ment and providing practical references in engineering construction.The soil particle size and salinity affect the freezing temperature of soil.This paper proposes a freezing temperature calculation model applicable to sulfate saline soils with salt analysis and different salinity.The study investigates the variations in freezing temperature for sodium sulfate free solution,sodium sulfate saline soil,and quartz sand.In the beginning,based on the prin-ciples of equal increments of chemical potential at the solid-liquid phase equilibrium,and the influence of the sol-ute in pore solution on water activity and ice crystal interface curvature effect was considered,and a freezing temperature prediction model was developed for aqueous solution,saline soils and quartz sand,respectively.Then,the freezing temperature was obtained through the freezing process tests on the saline soil with different salt contents.The experimental equipment includes a metal container with a lid,containing an inner diameter of 2.5 cm and a height of 3.5 cm,a temperature sensor,a vertical precision incubator,and a data collector.Final-ly,the accuracy and applicability of the model are validated by the root mean square error,significance level and the coefficient of agreement.Some conclusions were conducted in this paper.The results indicate that the lower the initial moisture con-tent in the soil sample,the stronger the capillary and adsorption effects on the soil surface,resulting in a lower freezing temperature.Additionally,when the water content of quartz sand exceeds its saturation water content and the water content of the soil surpasses its liquid limit,the freezing temperature of the pore solution tends to stabilize as the water content increases.The higher effective concentration of pore salt solution leads to the lower freezing temperature,and due to the influence of salt crystallization,the effective concentration initially increas-es with initial concentration.Specifically,when the concentration is less than 0.53 mol⋅kg-1,the freezing tem-perature decreases as the increasing of solution concentration.When the initial concentration is between 0.53 and 0.74 mol⋅kg-1,the solution concentration results increasing in salt crystallization,reducing the effective con-centration and increasing the freezing temperature.When the concentration is above 0.74 mol⋅kg-1,salt precipi-tation is complete,the effective concentration remains constant,and the freezing temperature tends to stabilize.The smaller soil sample pore radius results in a greater influence of ice crystal interface curvature,which leads to a lower freezing temperature.Specifically,when the pore radius is less than 0.55 μm and greater than the criti-cal pore radius of 0.003 μm,the freezing temperature of the soil sample decreases rapidly as the pore radius de-creases.Above 0.55 μm,the extent of the influence of interface curvature on freezing temperature is greatest in clay,followed by silty clay,then silt,and least in quartz sand.This paper provides a practical model for temper-ature in saline heave deformation of saline soils and artificial freezing method,which provides theoretical basis for numerical simulation in hydro-thermal-saline coupling.
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