Abstract: In order to study the humidification and deformation characteristics of intact loess under complex stress conditions, the double-line grading wetting tests on intact loess under measuring suction were carried out by using collapsing true triaxial apparatus for unsaturated soil. The variation characteristics of suction under the action of coupling stress and water were discussed. The humidification deformation characteristics of true triaxial soaking tests and the effects of suction, net confining pressure, intermediate principal stress and stress ratio on humidification deformation were studied. The results showed that the yield points of unsaturated soil were determined by the ei-lgp compression curves. Before the yield points, the slope of the curves were approximately equal. After the yield points, the slope reduced with the decrease of the initial suction, and the intersection points between unsaturated soil and saturated soil moved to the lower right with the increase of initial suction. In the process of isotropic compression, suction approximately linearly decreased with the increase of net average stress, the smaller the initial suction, the slower the suction decreased and the smaller the variation amount of suction. When grading soaking and humidifying under pressure equalization, suction s decreased with the increase of water immersion w, and the humidification volume strain enlarged with the increase of water immersion w. The -w relationship curves under different net confining pressures intersected with each other. Before the intersection area, the larger the net confining pressure, the smaller the humidification volume strain, and after the intersection area, the larger the net confining pressure, the larger the humidification volume strain. Under the same net confining pressure condition, when the water immersion amount was the same, the larger the initial suction, the larger the humidification volume strain. In the true triaxial shear humidification tests, the stress ratio k, the intermediate principal stress parameter b value and the net confining pressure ?3 all had a certain influence on the humidification deformation. When q/p≤1, the front section of the humidification deformation curve was lower concave, and the back section was upper concave, mainly showing volume humidification deformation. When q/p>1, the humidification deformation curve had only the lower concave part, which was mainly characterized by shear humidification deformation. The shape of the humidification deformation curve depended on different combinations of k and b values.

Key words: wetting deformation, intact loess, collapsing true triaxial apparatus, suction, intermediate principal stress, stress ratio