Abstract：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.
