氯化钠溶液饱和不同初始含水率膨润土的膨胀特性

Swelling characteristics of bentonite with different initial water contents saturated by NaCl solution

采用不同初始含水率控制土颗粒扩散双电层的形成程度,进行了一系列氯化钠溶液饱和膨胀试验,探究了具有不同扩散双电层厚度膨润土样在不同浓度氯化钠溶液中的膨胀特性,并对不同初始含水率膨润土样进行核磁试验。核磁试验结果表明,当初始含水率小于10%时,最优T2值不随着含水率增加而增加,根据T2值与水的赋存半径关系,说明此时土样只有强结合水存在,即土样强结合水率为10%。这与用其它方法算出的强结合水率基本一致,说明核磁共振技术可测定出土样的强结合水率。膨胀试验结果表明,当初始含水率小于10%时,不同浓度氯化钠溶液饱和试样时,其膨胀性基本不变;而用氯化钠溶液初始含水率大于10%试样时,随着其浓度的增加,膨胀率明显降低。造成上述差异的原因是,当只有强结合水存在时,试样被氯化钠溶液饱和后,土颗粒会吸附水化的阳离子,增加土颗粒固定电荷,导致膨胀力增加,增加试样的膨胀性,而随着溶液浓度的增加双电层厚度与膨胀力降低,会降低试样的膨胀性。

The effects of NaCl solution on the swelling characteristics of bentonite with different initial water contents are investigated by performing a series of wetting tests and nuclear magnetic resonance tests. The test results indicate that when the initial content is less than 10%, the optimal T2 do as not change with the increasing initial water content, and according to the relation between T2 and the radius of water, the soil has only strongly bound water. That is to say, the strongly bound water content is about 10% for the bentonite, which is the similar to that by other methods, thus the nuclear magnetic resonance can determine the water content of strongly bound water. The wetting test results indicate that when the initial water is less than10%, the NaCl solution has no effects on the swelling. When the initial water content is larger than 10%, the swelling strain decreases with the increasing NaCl solution concentration. The reasons for the above results are as follows: when the soil has only strongly bound water, it generates cationic hydration to increase in the fixed charge density of soil after immersed by the NaCl solution. It results in an increase in the swelling pressure, and thus results in the increasing swelling strain. The thickness of diffuse double layers and the swelling pressure decrease with the increasing NaCl solution concentration.