含氯硫酸盐渍土中硫酸钠结晶量理论分析研究

硫酸盐渍土产生盐胀变形的主要原因是土中固相或液相硫酸钠结合水分子析出芒硝晶体,盐分体积大幅增加而导致的。基于已有测试数据,采用回归分析方法建立了硫酸钠溶解度模型,在理想条件下分析计算了降温条件下土体内硫酸钠的结晶量,探讨了硫酸钠结晶量随含盐量、含水率、氯化钠浓度和土体环境温度的变化关系。研究表明,含盐量和含水率对硫酸钠结晶量的影响存在一个临界值,氯化钠浓度对硫酸钠结晶量的影响取决于土体内的含盐量和含水率组合条件,有利组合下加入适量氯化钠能够抑制土体内硫酸钠的结晶量,不利组合下加入氯化钠反而会促使土体内硫酸钠结晶量增大,不利于盐胀变形的控制。硫酸钠结晶量严重依赖于环境温度,若初始状态下土体的温度较低,部分硫酸钠已经结晶析出,温度进一步降低时硫酸钠的结晶量则相应减少。

Theoretical analysis of crystallization of sodium sulphate for sulphate saline soil containing chloride

Concerning the salt heaving within the sulphate salty soil, it is characterized by the crystallization of sodium sulphate. Specifically, the mirabilite (Na₂SO₄·10H₂O) can be precipitated directly from the saturated sodium sulfate solution under some conditions, and the solid volume of salt crystal consequently increases 4.18 times, which finally results in large salt heaving. By collecting experimental data, a static model is established to describe the soluble properties of sodium sulphate, which can be employed to analyze the crystal amount of sodium sulphate in soil. Using this model, the crystallization of sodium sulphate is analyzed and calculated in the cooling process. At the same time, the influences of salt content, water content, concentration of sodium chloride and soil initial temperature on crystallization are discussed. It is found that the critical values for salt content and water content exist for the crystallization of sodium sulphate. The influences of sodium chloride on crystallization of sodium sulphate depend on the coupled effects of salt content and water content. In case of the favorable combination, the crystallization in soil can be restrained by addition of sodium chloride. Contrarily, the sodium chloride can accelerate the crystallization of sodium sulphate. The crystal amount of sodium sulphate depends on the environment temperature seriously, and partial sodium sulfate is crystallized if the initial temperature of soil is low, which reduces the crystallization in further cooling process.