冻融循环作用下粉砂质硫酸盐渍土变形特性研究

Study on deformation characteristics of silty sulfate soil under freeze-thaw cycle

【目的】为探究南疆地区粉砂质硫酸盐渍土的变形特性,【方法】在封闭系统条件下对粉砂土进行冻融循环试验,利用扫描电镜对土体结构进行表征分析。【结果】结果显示:粉砂质硫酸盐渍土硫酸钠含量为0和1.0%时变形以融沉为主,5次循环后变形量分别为-1.30 mm、-1.02 mm;硫酸钠含量为2.0%、5.0%、8.0%时变形表现为盐胀-冻胀变形,5次循环后变形量分别为2.46 mm、8.53 mm、3.43 mm。【结论】结果表明:粉砂质硫酸盐渍土在冻融循环作用下温度和硫酸钠含量是影响土体发生冻融变形的主要因素。在低温区间土体的变形随温度的降低表现为盐胀-冻胀,在升温过程中土体先后出现冰融和盐溶变形;土体的最终变形量与硫酸钠含量的变化表现为先增后减,当硫酸钠含量为5.0%时,土体的盐-冻胀率达到最大为2.5%。运用扫描电镜可发现粉砂质硫酸盐渍土经冻融循环后在自重作用下会产生沉降,内部盐分重结晶是抑制沉降甚至造成土体膨胀的主要原因。

[Objective]In order to explore the deformation characteristics of silty sulfate soil in southern Xinjiang,[Methods]The freeze-thaw cycle test of silty soil was carried out under closed system conditions,and the soil structure was characterized and analyzed by scanning electron microscopy.[Results]The result showed that the deformation was mainly melt and precipitation when the sodium sulfate content of silty sulfate soil was 0 and 1.0%,and the deformation was-1.30 mm and-1.02 mm after five cycles,respectively.When the sodium sulfate content was 2.0%,5.0%and 8.0%,the deformation was salt expansion-frost heave deformation,and the deformation after five cycles was 2.46 mm,8.53 mm and 3.43 mm,respectively.[Conclu-sion]The result show that the temperature and sodium sulfate content of silty sulfate soil under freeze-thaw cycle are the main fac-tors affecting the freeze-thaw deformation of soil.The deformation of soil in the low temperature interval is manifested as salt expansion-frost heave with the decrease of temperature,and ice melting and salt dissolution deformation occur successively in the process of heating.When the sodium sulfate content is 5.0%,the salt-frost heave rate of the soil reaches a maximum of 2.5%.Using scanning electron microscopy,it can be found that silty sulfate soils will settle under their own weight after freeze-thaw cycles,and internal salt re-crystallization is the main reason for inhibiting settlement and even causing soil expansion.