黄土液化微细观特性试验研究

黄土液化演化过程的微观机理分析是液化防御的科学问题之一。通过微细观及动力学试验探索黄土液化的本质和影响因素。首先用CT细观扫描实验探索黄土渗透液化的细观变化,研究表明土体液面上升的根本原因是弱碱性盐类胶结物的吸水作用导致土样含水面整体上升;试样达到高饱和度,大孔隙周围颗粒间胶结物质破坏后有效应力为零,土层液化。粉土的孔隙尺寸和特殊的胶结物质导致高饱和度。土样微观结构的差异也会影响土的液面上升和破坏强度。针对低黏性粉土、粉质砂土及粉质黏土的三类黄土液化实验分析表明,低黏性粉土动荷加载时间更短,更易于液化,即低粘性粉土液化最为严重,粉质砂土为中等液化,粉质黏土相比其他黄土类别不易液化。电镜扫描土样微观结构参数分析表明,土颗粒周围胶结物质的化学元素比值(Ca/Fe),以及土颗粒粒径分布和孔隙尺寸(孔隙与颗粒比)均影响液化等级,可初步判断液化的强弱。

Experimental Investigation of Micro-mesoscopic Features of Loess Liquefaction

Nowadays, the microscopic analysis of the evolution process mechanism of loess liquefaction is a hot topic. In this study, we attempt to investigate the nature and influence factors of loess liquefaction through dynamic tests. We use the CT scanning test to study the macroscopic change of loess liquefaction. The results show that the primary cause of liquid level rise is the water absorption of alkalescent salt cement. When specimens become highly saturated, the cementing material between the particles surrounding the soil macropores is destroyed. Then, the effective stress is zero and the soil is liquefied. The difference in the microstructure of soil can also influence the increase in liquid level and the failure strength of soil. Liquefaction tests on three kinds of loess (low-cohesive silt, silty sand, and silty clay) indicate that the dynamic loading time of the low-cohesive silt is the shortest. In other words, the liquefaction of low-cohesive silt is most severe and the silty sand is in medium liquefaction; by comparison, the silty clay is difficult to liquefy. The analysis of soil microstructure parameters with scanning electron microscope indicated that the chemical element (Ca/Fe) ratios of the cements around the soil particles, and the particle size distribution and pore size of the soil particles affect the degree of liquefaction.