Experimental study on the influence of soluble salt content on unsaturated mechanical characteristics of undisturbed Ili loess

Due to the perennial influence by west wind climate, the loess in Ili, China, is obviously different from that in the loess plateau of the monsoon area, showing the characteristics of large collapsible deformation and high soluble salt content. During the operation of hydraulic structures such as canals, the distribution of soluble salt content in the surrounding unsaturated soil is uneven due to the movement of water, which affects the deformation and safety of construction projects. In order to reveal the mechanical characteristics of the undisturbed unsaturated Ili loess with different soluble salt contents, the net mean stress increase and decrease tests of controlling suction, the suction increase and decrease tests of controlling net mean stress, and the consolidation shear tests of controlling net confining pressure and suction were carried out under different soluble salt contents, to explore the influence of soluble salt content on the characteristics of deformation, yield, strength, and water content. The results show that the soluble salt content has a critical value to improve the cementation between particles, and there exist maximum yield values of net mean stress, yield shear stresses, and shear strength with the soluble salt content of 14–20 g/kg, corresponding to the maximum structural strength and elastic region. The rebound coefficient increases with the increase of the initial rebound pressure. With the increase of soluble salt content, the water discharge of the consolidation stage and the compressibility index are decreasing. The degree of saturation is more affected by the soluble salt content in the transition zone. For a certain soluble salt content, the initial and subsequent yield curves are approximately assumed to be ellipses that are symmetrical to the initial stress state line, and the hardening effect produced by stress and suction is isotropic. The above results verify the LC and SI yield curves of unsaturated Ili loess and reveal the shape and hardening law of yield curves in the p-q plane, which offer model parameters for the establishment of the humidification deformation constitutive model and provide reference for the prediction of unsaturated mechanical and hydraulic properties in the Ili area.