氯离子对盐渍化寒区路基填土盐胀的影响研究

Effect of Chloride Ions on Salt Expansion of Salinized Subgrade Fill Soil in Cold Regions

盐渍化寒区路基填土通常为富含氯化钠和硫酸钠的复合盐渍土。为探究氯离子含量对盐渍化寒区路基盐胀的影响机制,基于Pitzer离子模型中氯化钠-硫酸钠-水三元体系溶液计算理论,结合FREZCHEM模型,定量分析水分活度、成冰因子和过饱和比与温度、浓度比(η=m_(Cl^(-))/m_(SO_(4)^(2-)))的内在关联,研究了复合盐渍土的冻结温度和结晶过饱和比随硫酸钠含量、浓度比的变化规律,揭示了氯化钠对硫酸盐渍土结晶的影响机制,确定了硫酸盐渍土中添加氯化钠降低盐胀的临界浓度比。研究结果表明:FREZCHEM模型可用于分析复合盐渍土的冻结和盐分结晶特性,成冰因子与温度和溶液浓度密切相关,当其等于1时,孔隙溶液处于热力学平衡状态;氯化钠对硫酸钠结晶析出具有促进或抑制双重作用,当盐渍土中硫酸钠的浓度大于1.0 mol/kg时,按照临界浓度比大于2.5添加氯化钠,会显著降低硫酸盐渍土的盐胀变形。同时,现场施工中采用盐化法可有效抑制盐渍化寒区路基的盐胀变形。

Salinized subgrade fill soil in cold regions typically comprises composite saline soil rich in sodium chloride and sodium sulfate.This study aimed to explore the mechanism of the effect of chloride ion content on salt expansion of the salinized subgrade in cold regions.Based on the calculation theory of the sodium chloride-sodium sulfate-water ternary system solution in the Pitzer ion model and combined with the FREZCHEM model,the study quantitatively analyzed the intrinsic connection between water activity,freezing factor,and supersaturation ratio with temperature and concentration ratio(η=m_(Cl^(-))/m_(SO_(4)^(2-))).It investigated the variation patterns of the freezing temperature and crystallization supersaturation ratio of composite saline soil with sodium sulfate content and concentration ratio,revealed the impact mechanism of sodium chloride on the crystallization of sulfate saline soil,and determined the critical concentration ratio for adding sodium chloride to sulfate saline soil to reduce salt expansion.The results show that the FREZCHEM model can be used to analyze composite saline soil’s freezing and salt crystallization characteristics.The ice formation factor is closely related to temperature and solution concentration,and when it equals 1,the pore solution is in thermodynamic equilibrium.Sodium chloride has a dual role in promoting or inhibiting the crystallization of sodium sulfate.When the concentration of sodium sulfate in the saline soil exceeds 1.0 mol/kg,the salt expansion deformation of sulfate saline soil will be significantly reduced by adding sodium chloride according to a critical concentration ratio greater than 2.5.Meanwhile,the salinization method applied during on-site construction can effectively suppress the salt expansion and deformation of the roadbed in saline cold areas.