单向冻结条件下硫酸钠盐渍土的冻结温度试验研究

Experimental Study on Freezing Temperature of Sodium Sulfate Saline Soil under Unidirectional Freezing Condition

硫酸钠盐渍土具有明显的随季节温度变化而发生土体结构改变的特性,给工程造成较大危害。为了研究单向冻结条件下硫酸钠盐渍土的冻结温度特性,在室内配制初始含水率分别为15%、17%、19%、21%,含盐量分别为0%、1%、2%、3%、5%的硫酸盐渍土试样,采用可控温冰柜进行单向冻结试验。结果表明:①同一土体,不同位置处冻结温度相同,但达到冻结温度所需时间存在略微差异。②初始含水率和含盐量对硫酸钠盐渍土冻结温度有很大的影响,当硫酸钠含盐量为1%和2%时,冻结温度随初始含水率的增加呈“先陡后缓”型变化趋势,并在最优初始含水率时达到最大值,之后冻结温度随初始含水率变化曲线趋于平缓;当含盐量较高(5%)时,冻结温度随初始含水率增加近似呈线性增加趋势。③硫酸钠盐渍土冻结温度随含盐量的增加而降低,且盐量为1%~2%时,不同初始含水率土体冻结温度及达到冻结温度所需时间随含盐量均呈“归一性”变化趋势。在计算硫酸钠盐渍土冻结温度时,应将硫酸钠溶液视为非理想稀溶液。在同一初始含水率条件下,对硫酸钠含盐量与冻结温度按三次多项式进行拟合吻合度较高。该研究成果可为硫酸盐渍土地区工程建设提供参考。

The structure of sodium sulfate saline soil is prone to change with seasonal temperature,which is detrimental to projects.To study the freezing temperature characteristics of sodium sulfate saline soil under unidirectional freezing condition,we carried out unidirectional freezing test by using a controlled temperature freezer on indoor-prepared samples with initial moisture content of 15%,17%,19%and 21%and salt content of 0%,1%,2%,3%and 5%.Results manifest that:1)The time required to reach freezing temperature differs slightly at different locations in the same soil despite the same freezing temperature.2)The initial moisture content and salinity of sulfate saline soil has a remarkable influence on freezing temperature.When the salinity of sodium sulfate is 1%and 2%,the freezing temperature first changes sharply but then gently with the increase of initial water content;the maximum freezing temperature is reached at optimal water content,and afterwards,the curve of freezing temperature tends to be flat with the change of initial water content.When salt content is high(5%),the freezing temperature rises linearly with the increase of initial water content.3)The freezing temperature of sodium sulfate saline soil declines with the increase of salt content.When salt content is 1%-2%,the freezing temperature of soil with different water content and the time required to reach freezing temperature all presents a trend of“normalization”.Sodium sulfate solution should be regarded as a non-ideal dilute solution in the calculation of freezing temperature of sodium sulfate saline soil.In addition,at the same initial water content,the relationship between sodium sulfate salt content and freezing temperature can be well fitted by cubic polynomial.