非饱和土体水平冻结过程中的水热耦合作用机制研究

Study on Moisture-Heat Coupling Mechanism during Horizontal Freezing of Unsaturated Soil

土体在冻结过程中伴随热量传递、冰水相变、水分迁移等演化过程,其水热耦合作用机制非常复杂。为此,在进行演化方程组解耦、冻结锋面精细化处理的同时,采用土体冻结特征曲线改进未冻含水量计算,引入总含水量优化冰组分生成,提出一种新的水平冻结水热耦合理论计算模型。基于隐式有限差分方法对该模型进行数值求解,结合试验结果验证其有效性。最后,以张掖壤土为研究对象,分析非饱和土体的水热耦合演化规律。研究表明,土体在冻结过程中,未冻区的水分会向冻结区迁移,在锋面位置处发生水分积聚;在孔隙率相同的情况下,土体的初始含水量越高,其温度下降速度越快,冻结区含水量的增加也更为显著。土体的冷源温度越高,冻结锋面的发展速度越慢,从而使得水分迁移时间更为充分,对应的冻结区平均含水量越高,水分积聚现象也越突出。冰阻抗在冻结锋面附近影响土体中的水分迁移,使其含水量及热扩散系数下降,从而影响温度场的演化。

The freezing process of soil is accompanied by the evolution of heat transfer,ice-water phase transition and moisture migration,with complex moisture-heat coupling mechanism.Therefore,a new moisture-heat coupling model of unsaturated soil during horizontal freezing was proposed by applying the soil freezing characteristic curve to improve the calculation of unfrozen water content and introducing the total moisture content to optimize the generation of ice,while decoupling the evolution equations and refining the treatment of freezing front.The implicit finite difference method was applied to numerically solve the proposed model,and the effectiveness was verified by the test results.Finally,the moisture-heat coupling evolution of unsaturated soil was studied based on the loam of Zhangye,Gansu province.The results show that the moisture in the unfrozen zone migrates to the frozen zone during the soil freezing process,which accumulates at the freezing front position.With the same porosity,the higher the initial moisture content of the soil,the faster the temperature drops,and the more significant the increase of moisture content is in the frozen zone.The higher the cold source temperature of the soil,the slower the development of freezing front,resulting in more time for moisture migrating.The higher the average moisture content in the corresponding frozen area,the more prominent the moisture accumulation.The ice impedance affects the moisture migration near the freezing front,causing a decrease in the moisture content and thermal diffusion coefficient,thereby affecting the evolution of the temperature field.