Abstract: In order to explore the critical state characteristic of high soluble salt loess in Ili area, a series of triaxial consolidation shear tests controlling suction and net confining pressure is performed on the unsaturated undisturbed Ili loess with different soluble salt contents. The results show that the strength of the unsaturated undisturbed Ili loess has a peak value with the increase of soluble salt content under the consolidation shear of constant suction. The q-p or e-p critical state lines are parallel lines of unsaturated soil with a certain soluble salt content under different suctions. The q-p' critical state lines under different suctions can be normalized as a straight line represented by the saturated critical state line, and the slope of the straight line decreases as a power function with the increase of soluble salt content. The slope ( ) of e-p critical state line of unsaturated soil is larger than the counterpart ( ) of saturated soil, both first decrease and then increase with the increase of soluble salt content. Under the same effective net mean stress, the ratio of critical state void ratio ( ) between unsaturated soil and saturated soil and gas saturation (1– ) can be normalized. The initial and subsequent yield curves in the q-p plane can be approximately assumed to be ellipses that symmetrical to the line. The hardening effect produced by suction and stress on the yield curve is isotropic.

Key words: unsaturated Ili loess, constant suction triaxial test, soluble salt content, yield, critical state line