陕西渭北晚更新世黄土-古土壤结合水膜厚度的试验研究

Experimental study on the bound water film thickness of Late Pleistocene loess-paleosol in the Weibei region of Shaanxi

为深入剖析黄土与古土壤工程性质的影响因素,以陕西渭北晚更新世黄土与古土壤为研究对象,基于核磁共振、比表面积测试并结合理论分析对结合水膜厚度进行研究。试验结果显示:黄土与古土壤的结合水膜厚度存在明显差异,黄土的结合水膜厚度明显大于古土壤,原因在于古土壤孔隙体积及孔径小于黄土,而古土壤中高价阳离子含量大于黄土,同时古土壤颗粒表面分布铁锰质薄膜,其亲水性较弱。分析结合水膜与黄土湿陷性、回弹变形等工程特性间的关系,发现黄土-古土壤的湿陷性随结合水膜厚度的增大而增强,随结合水膜厚度的减小而减弱,结合水膜厚度与卸荷变形系数呈正相关关系。综合分析说明,高价阳离子含量、颗粒表面特性,及孔隙性的不同造成了黄土与古土壤结合水膜厚度的差异,从而导致黄土与古土壤的湿陷性等工程性质有显著区别。

The thicknesses of bound water film of Late Pleistocene loess and paleosol in Weibei,Shaanxi Province,were studied based on nuclear magnetic resonance,specific surface area tests,and theoretical analysis to comprehensively analyze the influencing factors of the engineering properties of loess and paleosol.Experimental results show that the thickness of the bound water film of loess is larger than that of paleosol,and a considerable difference is observed between their thicknesses.This difference can be attributed to the smaller pore volume and size of paleosol than those of loess,while the content of high-valence cations in paleosol is greater than that in loess.In addition,the surface of paleosol particles is distributed with an iron-manganese film;therefore,its hydrophilicity is weak.The relationship between bound water film and engineering characteristics of loess,such as collapsibility and rebound deformation,was analyzed.The collapsibility of loess-paleosol increases with the thickness of bound water film and decreases with the thickness of bound water film.The thickness of the bound water film is positively correlated with the unloading deformation coefficient.Comprehensive analysis shows that the variations in high-valence cation content,particle surface characteristics,and porosity contribute to the difference in bound water film thickness between loess and paleosol.This phenomenon leads to differences in engineering properties,such as collapsibility between loess and paleosol.