Influence of structure on shear characteristics of the unsaturated loess in Lanzhou, China

Loess is typically a kind of soil with metastable structure, which makes loess sensitive to collapse and sliding upon wetting. Such structure has thus profound influence on loessʹs mechanical behavior. However, there have been arguments about how the metastable structure influences on loessʹs mechanical behavior and what the mechanism behind is. In this study, the influence of structure on shear characteristics of the unsaturated loess in Lanzhou city of China was investigated with comparison of variation of shear strength and its parameters between six pairs of the undisturbed and remolded samples. It is found that the peak shear strength and strength parameters of the loess significantly reduced once its structure was destroyed, while shear behavior of the loess showed little change. Strength parameter c was much more sensitive to structure of the loess than ϕ. Shear strength reduction of the loess due to change of structure should be largely attributed to breaking up of cementation bonds between particles, evidenced by the difference in pore size distribution and microstructure of soil fabrics between the undisturbed and remolded samples. The bonds provided by clays and carbonates contributed the most to structure of the loess with minor by soluble salts, while matric suction played little role in structure of the loess.