Rheological properties of the high soluble salt content Ili loess with different water contents

Rheology can be often used to reveal the flow and deformation of viscoelastic materials, in terms of mechanical stability and long-term deformation parameters of soil structures. This study aims to explore the influence of moisture content and soluble salt content on the rheological characteristics and structural stability of Ili loessial soil in Northwest China. A series of steady-state and dynamic rheological tests were also carried out for the Ili loessial soil with the different contents of moisture and soluble salt using the rheometer. Firstly, the shear rate/shear strain and shear stress curves were obtained with the different water volume fractions and soluble salt content under steady and dynamics. The Bingham model was introduced to fit the rheological curve under a small shear rate. Secondly, the viscosity curves were also obtained under different water volume fractions and soluble salt content. Finally, an analysis was made on the evolution in the steady-state and dynamic rheological properties of soil structure. Meantime, the influence of moisture and soluble salt content on steady-state and dynamic rheological parameters was investigated to quantitatively analyze the relationship between rheological parameters and each variable. The results show that the soil was changed from the solid to the quasi-solid state in the steady-state shear process, and finally tended to the flow state. The shear stress increased first and then decreased with the increase in the shear rate. The Ili loessial soil conformed to the Bingham model at the low shear rate (10-4-5×10-4 s-1). The yield stress and viscosity decreased with the increase in moisture and soluble salt content. Specifically, the yield stress was between 300 and 1100 Pa. The viscosity with different water content decreased with the increase of shear rate, ranging from 1 to 107 Pa•s. The Ili loessial soil exhibited the shear thinning behavior. The shear stress increased first and then decreased with the increase of shear strain under dynamic shear. There was a linear decrease in both dynamic shear strength and viscoelastic parameters (including the storage and loss modulus, linear viscoelastic shear stress, yield shear stress, the maximum shear stress, shear strain at the maximum shear stress, yield point strain, and integral z) with the increase of moisture and soluble salt content, indicating the decrease in the stability of soil structure. Once the moisture content reached 27.5%, there was a weak influence of soluble salt content on these parameters. There was no change in the loss factor at the shear strain of less than 0.1%, where the soil was in the linear viscoelastic zone. The loss factor increased gradually when the shear strain was greater than 0.1%. The soil with the high moisture and soluble salt content reached the yield point first, indicating that the high moisture and soluble salt content were not conducive to the stability of the soil structure. The influence of soluble salt content on the rheological parameters decreased with the moisture content. Therefore, the rheological properties of Ili loessial soil were characterized qualitatively and quantitatively. The finding can provide a strong reference for further understanding of the viscoelastic properties of loessial soils.