Abstract: A series of collapsibility tests on Q2 loess of Pucheng power plant in Shaanxi province under 1D and 3D stress conditions were conducted using GDG high pressure oedometer and unsaturated collapsible triaxial apparatus. Under 1D stress condition, the collapsibility of Q2 loess is moderate or weak. The maximum coefficient of collapsibility decreases with the increase of depth. The Q2 loess is not collapsible under low pressure, but it is possibly collapsible under high pressure. The collapsibility of Q2 loess layer is stronger than that of ancient layer. The collapsibility sensibility of Q2 loess is weaker. Large-scale projects should use actual pressure to evaluate collapsibility of Q2 loess. Under 3D stress condition, curves of collapsible strain in terms of quantity of wetting are divided into three stages: the collapsible strain increasing slightly, the collapsible strain increasing rapidly and the collapsible strain being almost unchanged. The influences of net confining pressure, deviatoric stress and suction, especially the latter two, on the collapsible strain during the process of wetting are obvious. The collapsible volumetric strain increases with the increase in the collapsible deviatoric strain and the relationship is almost linear.

Key words: Q2 loess, wetting, triaxial, collapsibility