Abstract:

 To explore the influence of osmotic suction on the compression, yield, and critical state characteristics of unsaturated loess under three‑dimensional stress conditions, isotropic compression tests and constant p & constant b shear tests were conducted on loess with different pore water salinities by means of a suction‑controlled unsaturated true triaxial apparatus. The results show that the isotropic compression curve gradually moves down with the increase of osmotic suction, and the yield stress shows a decreasing trend. The shear strength decreases with the increase of b value and increases with the increase of osmotic suction. Under different b values, the critical state line in the p-q plane can be normalized to the critical state line of saturated loess by using the effective net mean stress, and the slope M increases with the increase of osmotic suction. The plastic potential surfaces in the meridian plane are elliptical. In the meridian plane, the plastic potential surfaces exhibit an elliptical shape. As the osmotic suction escalates, the major axis progressively diminishes in length, whereas the minor axis experiences an elongation. The critical state line in the e-lgp plane (e is the void ratio of unsaturated soil) exhibits an upward shift as osmotic suction increases, accompanied by a gradual reduction in the slopes denoted by λ₀, λ₁. The ratio of the critical state void ratio of unsaturated loess to that of saturated loess, denoted as e/e_s, exhibits a normalized relationship with the gas saturation (1−S_r, S_r is the degree of saturation of soil in the critical state). Furthermore, by incorporating the osmotic suction π , a three-dimensional predictive model is developed for determining the critical state void ratio of unsaturated saline loess.

Key words: unsaturated true triaxial test, saline loess, osmotic suction, critical state characteristics