基于结合水膜厚度变化的红黏土收缩机理研究

Shrinkage mechanism of red clay based on changes in the thickness of bound water film

结合水的含量及存在形式对红黏土的物理力学性质具有重要影响,而红黏土宏观收缩会引起土粒、孔隙、结合水微观结构变化,进而可能产生土体浅表层开裂引发渗透、失稳等工程地质问题。采用热重分析试验、BET测试试验、电镜扫描和Zeta电位试验对原状红黏土收缩过程中结合水的变化特征进行了研究,建立了基于结合水膜均匀分布下的球状和薄片状黏土颗粒结构模型,并推导出结合水膜厚度的计算公式。研究结果表明,原状红黏土中的水分大部分以结合水的形式存在,红黏土的收缩过程一直贯穿着弱结合水的损失,Zeta电位和比表面积不断减小,结合水膜厚度也不断减小。研究结果揭示了红黏土失水收缩的内在机理,可为解决环境工程地质问题提供理论支持。

[Objective]The content and existence form of bound water have an important influence on the physical and mechanical properties of red clay,and macroscopic shrinkage of red clay leads to microstructure changes of soil particles,pores and bound water,which in turn may cause soil surface cracking,triggering infiltration,destabilization,and other engineering geological problems.[Methods]Thermogravimetric analysis tests,BET tests,scanning electron microscopy(SEM)and zeta potential tests were conducted to study the variation characteristics of bound water during the shrinkage of undisturbed red clay.The structural model of spherical and lamellar clay particles based on the uniform distribution of bound water film was established,and the formula for the calculation of bound water film thickness was derived.[Results]The results showed that most of the water in undisturbed red clay exists in the form of bound water and the loss of weakly-bounded water continues throughout the shrinkage process of red clay.During the process,the zeta potential,specific surface area and the thickness of the bound water film decreased continuously.[Conclusion]The results reveal the intrinsic mechanism of water loss and shrinkage of red clay,which can provide theoretical support for solving environmental engineering geological problems.