黄土在受力和湿陷过程中微结构变化的CT扫描分析

ANALYSIS OF MICROSTRUCTURE CHANGE FOR LOESS IN THE PROCESS OF LOADING AND COLLAPSE WITH CT SCANNING

进行了原状黄土三轴剪切、浸水湿陷试验过程的 CT 扫描,根据 CT 图像、数据,利用损伤理论,分析了原状黄土在以上过程中的微结构变化。认为由于围压没有超过结构强度的临界值,损伤破坏表现出软化开裂破坏,整个过程是由轴向压密损伤为主导向横向开裂损伤为主导的转变过程,裂缝首先在结构强度较低的低密软弱大孔隙区域形成,随后衍生出一系列小裂缝,最终形成剪切面。硬化屈服损伤破坏后期的强度增长是靠材料的挤压导致的密度提高和截面积的增长来共同维持的,并稳定在一个水平上。由试验可知,原状黄土在湿陷过程中发生了某些物理化学变化,大孔隙对黄土的湿陷没有必然的贡献。

The triaxial shear test, soaking test, and CT scanning during soaking are carried out on intact loess specimens. According to images and data of the CT scanning, the microstructure change of the samples is analyzed by means of damage theory. It is shown when the confining pressure is less than the critical structural strength of the sample, the damage destruction exhibits softening dehiscence. During the course of damage, there is a change from axial dominant density damage to crosswise dominant dehiscence damage. In the area containing a variety of big holes, fractures first appear where the structure strength is weak with low density, and then a variety of small fractures are produced which subsequently change into one single shear surface. For hardening yield damage, the later strength depends on the increase of density and sectional area of the sample. It is found that some physical and chemical changes occur in the collapse process and the big pores in loess do not always contribute to collapsibility.