Abstract：The collapsability test for undisturbed Q3 loess under suction control is studied with stress controlled triaxial apparatus. 15 CT-triaxial tests are performed，including double-triaxial unloading confining pressure tests and isotropic compression tests. During the tests，computerized tomography(CT) is employed. Using the CT data，the effect of the Q3 loess¢s structure is analyzed. The results show that，for the double triaxial collapsible tests，collapsible deformation increases with net confining pressure increasing，including the volumetric strain，axial strain and deviator strain. For the isotropic compression collapse tests，the relationship between water content and the CT data is linear before the specimen is saturated. The CT data increasing velocity will slow down with high enough saturation. For the isotropic compression collapse tests，if the specimen has the same suction，the high net confining pressure versus big volumetric strain，and the value of the structural evolution have the same rule，too.
