压实红黏土的恒体积膨胀力与细观机制研究

针对目前量测土体膨胀力的主要方法所存在的不足,提出近似完全限制条件下测量土体膨胀力的改进方法。以压实红黏土为研究对象,测到不同初始状态(含水率、干密度)试样的膨胀力,并与膨胀反压法测得的膨胀力进行对比分析,发现限制膨胀方法测得的膨胀力要小于膨胀反压法的试验值。同时,显现出限制膨胀法测膨胀力具有3个主要优点:试验过程中保持土体不发生变形,更加符合膨胀力的物理定义;试验耗时少、占空间少;能测较宽含水率范围内的膨胀力。最后,利用压汞法和氮吸附法测得不同状态下土体的细观孔隙结构分布特征。结果表明:相同干密度试样,制样含水率对压实土体的孔隙分布影响显著;黏土晶间和粒间吸水自由膨胀后发生"不可逆"膨胀变形;土体发生"不可逆"膨胀变形程度是引起限制膨胀法和膨胀反压法所得试验结果出现差异的主要原因。

Swelling pressure and mesomechanism of compacted laterite under constant volume condition

There are many defects of the main soil swelling pressure measuring methods at present. So, an improved method is put forward which could measure the soil swelling pressure under approximately completely restricted swelling conditions. Taking compacted laterite as study object, the swelling pressures of specimens have been measured at different initial water contents and dry densities. Comparing with the test results which belong to swell-consolidation method, it is indicated that the former swelling pressure values are less than the later ones. Meanwhile, the restricted swelling method has three major advantages. Firstly, it accords well with the definition of swelling pressure owning to the soil un-deformation after soaking. Secondly, it takes less time and occupies smaller space. Thirdly, it can measure swelling pressure within wide range of water content. Furthermore, the samples mesoscopic pore size distribution features under different conditions have been measured by mercury intrusion method and nitrogen adsorption method. The results show that the influence of sample water content is significant on the pore distribution of compacted laterite at the same dry density. The compacted laterite occurs “irreversible” swelling due to the incursion of water molecule into laterite crystal and grain. The “irreversible” swelling degree of laterite is major reason which brings to difference swelling pressure values between the restricted swelling method and swell-consolidation method.