为了研究黄土的非饱和增湿变形特性,对不同压实度的黄土分别进行分级浸水的增湿变形试验,对其从非饱和状态增湿至饱和过程中的变形特性进行对比研究,提出了压实黄土增湿变形的临界孔隙比。通过扫描电镜试验(SEM)和压汞试验(MIP),分析了压实黄土的增湿变形特性与其微观结构之间的关系。结果表明:竖向应力条件下,当压实黄土的初始孔隙比大于临界孔隙比时,孔隙比将随饱和度增大呈指数函数递减,并趋向于临界孔隙比;当压实黄土的初始孔隙比小于临界孔隙比时,孔隙比随饱和度增大不变。压实度为70%时,黄土内部具有大量大于颗粒尺寸的大孔隙,增湿变形较强;压实度达到90%时,黄土内部孔隙尺寸远小于大部分颗粒尺寸,增湿变形很弱。在水力耦合作用下,压实度为70%的黄土的孔隙结构变化很大,颗粒边角相互摩擦变圆,颗粒排列定向性明显加强;而压实度为90%的黄土的孔隙结构变化较小,集粒内部弱胶结作用的破坏使颗粒更趋于棱角状,颗粒排列定向性无明显变化。研究结果为明确黄土的增湿变形机制提供了参考。
Abstract
To investigate the unsaturated wetting deformation of loess, staged water-saturation test is conducted on loess specimens of different compactness degrees. The critical void ratio for the wetting deformation of compacted loess is proposed by comparing the deformation behaviors of loess among different stages from unsaturated to saturated state. In addition, scanning electron microscope (SEM) and mercury intrusion porosimetry (MIP) are adopted to analyze the correlation between wetting deformation behavior and microstructure evolution. Results are concluded as follows: 1) under a constant vertical pressure, the void ratio of loess specimen decreases exponentially with the rising of saturation degree and finally reduces to the critical void ratio when its corresponding initial void ratio is greater than critical void ratio; while when initial void ratio is lower than critical void ratio, void ratio exhibits no change. 2) When the compactness degree is 70%, strong wetting deformation is resulted from large amounts of inner pores with sizes larger than most particle sizes, while loess with a compactness of 90% presents an opposite trend. 3) Under loading and wetting actions, the pore structure of loess with a compactness of 70% varies significantly, with particles getting rounded and particles’ predominant orientation reinforced; while for loess with a compactness of 90%, the pore structure changes slightly with no obvious change in particles’ predominant orientation, and particles tend to be angular due to the weak cementation among particles.
关键词
压实黄土 /
非饱和 /
增湿变形 /
临界孔隙比 /
微观结构
Key words
compacted loess /
unsaturated /
wetting deformation /
critical void ratio /
microstructure
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基金
教育部博士点基金项目(20110211110025)
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