物理化学效应对膨胀土收缩特性的影响机制

Mechanism of physicochemical effect on the shrinkage of expansive soil

膨胀土由于其骨架带有较多的固定负电荷,层间存在与负电荷平衡的可交换阳离子,使得土体呈现较强的胀缩性。研究结果表明,膨胀土的胀缩性会受到孔隙溶液化学成分的影响。选用广西地区的强膨胀土作为研究对象,开展了不同浓度的NaCl溶液对膨胀土土-水特征曲线和收缩曲线影响的试验研究,引入了粒间应力的概念对收缩曲线进行描述,该粒间应力考虑了渗透、毛细和吸附的影响。结果表明:孔隙盐溶液是通过渗透吸力对土-水特征曲线产生影响,对基质吸力的影响较小。土样在脱湿过程中的收缩变形是由粒间应力来控制的,类似于加压固结现象。大部分的收缩都发生在毛细阶段,为弹塑性变形;吸附阶段的收缩较少,为弹性变形。通过识别压缩曲线上的弹塑性分界点可以得出毛细和吸附作用的分界点,该分界点与独立测量的不同密实度下的持水曲线结果一致。结果表明,粒间应力能够更好地描述膨胀土的化学-力学行为,特别是在低含水率条件下。

Due to the fixed negative charges in the skeleton of expansive soil,there are exchangeable cations between the layers that balance the negative charges in expansive soil.That makes the soil exhibit strong expansion and shrinkage properties.The research results show that the expansion and shrinkage of expansive soil will be affected by the chemical composition of the pore solution.In this paper,based on the strong expansive soil in Guangxi,a series of tests are carried out to investigate the soil-water retention curve(SWRC)and the soil shrinkage curve(SSC)for the soil saturated with solutions of different NaCl concentrations.To address this issue,the concept of intergranular stress is introduced,which takes into account the effects of osmosis,capillary,and adsorption.The results show that pore saline solution affects the SWRC through osmotic suction,with a lesser effect on matric suction.The shrinkage deformation of soil samples during the drying process is controlled by intergranular stress,similar to the phenomenon of pressure-induced consolidation.The majority of shrinkage occurs during the capillary stage,exhibiting elastoplastic deformation;less shrinkage occurs during the adsorption stage,which is characterized by elastic deformation.A cutoff point on the compression curve is identified to distinguish between the regimes of capillarity and adsorption,consistent with the independently measured SWRCs at different compactness.The intergranular stress is shown to better describe the chemo-mechanical behavior of expansive soil,particularly at low water content.