复杂冻融循环条件下土体水盐迁移规律试验研究

Experimental Study on Water and Salt Transport Law of Soil Under Complex Freeze-Thaw Cycle Conditions

摘要:

为研究土体中的水盐迁移规律,以砂质黄土为研究对象,开展了无压补充0.8%和1.5%浓度的硫酸钠溶液条件下,冻融、冻融-蒸发和冻融-蒸发-降雨3种工况下的冻融循环试验,探究了冻融、蒸发和降雨过程中土体的水盐迁移规律,对试验土柱的温度、水分和电导率在不同工况下的变化规律进行了分析。研究表明:冻融循环下土体温度变化存在滞后现象,土体温度变化幅度随土体深度增大而减小;3种工况下土体含水率和电导率均呈周期性变化,冻融循环结束后土体水、盐含量均增大,蒸发作用使盐分随水分向上迁移并导致土柱顶部盐分过饱和析出,降雨作用使土柱上部盐分随水分向下迁移;在相同工况下,补给溶液浓度高时更有利于上部土体的盐分积累,当无压补充0.8%浓度盐溶液时,在3种工况下,土柱上部电导率的增长量分别为0.12、0.31、0.45 dS/m,当无压补充1.5%浓度盐溶液时,3种工况下土柱上部电导率增长量依次增至0.27、0.36、0.52 dS/m;土体盐分变化受到温度、浓度梯度和作用时间的综合影响,冻融-蒸发-降雨循环下上部土体电导率增长最多。

Abstract:

To study the water-salt migration patterns in soil, using sandy loess as the research object, we conducted freeze-thaw, freeze-thaw-evaporation, and freeze-thaw-evaporation-rainfall three types of cycle tests under the conditions of unpressurized supplementation of 0.8% and 1.5% concentration sodium sulfate solution. We explored the water-salt migration patterns of the soil during freeze-thaw, evapo-ration, and rainfall processes, and analyzed the changes in temperature, moisture, and conductivity of the test soil column with respect to the working conditions. The results show that there is a lag phenomenon in the temperature changes of the soil during freeze-thaw cycles, and the amplitude of temperature changes decreases with the increase of soil depth. In all three working conditions, the moisture content and conductivity of the soil show periodic changes. After the freeze-thaw cycle, the water and salt contents of the soil increase. Under evaporation conditions, the salt is transported upward with water and causes oversaturation precipitation at the top of the soil column. Under rainfall conditions, the salt in the upper part of the soil column moves downward with water. Under the same working conditions, a higher concentration of the replenishing solution is more conducive to the accumulation of salt in the upper soil layer. When the unpressurized replenishing solution is 0.8% concentration, the increase in conductivity of the upper part of the soil column in the three working conditions is 0.12, 0.31, and 0.45 dS/m respectively. When the unpressurized replenishing solution is 1.5% concentration, the increase in conductivity of the upper part of the soil column in the three working conditions increases successively to 0.27, 0.36, and 0.52 dS/m. The changes in soil salt content are influenced by the combined effects of temperature, concentration gradient, and action time. Under the freeze-thaw-evaporation-rainfall cycle, the increase in conductivity of the upper soil layer is the greatest.