The structure of loess is an important physical property indicator. Just like grain size, moisture content and density, it also affects the physical and mechanical properties of loess. Based on the definition of the constitutive degree index, the definition of structural parameters was redefined. And conventional triaxial shear tests were conducted on undisturbed soil samples and remolded soil samples with different moisture contents and different dry densities. Firstly, the deformation characteristics and strength changes of the soil samples were analyzed. Then, based on the definition of structural parameters, the structural change laws of the soil were analyzed. Finally, the relationships between the structural properties and soil moisture, grain size and density were analyzed, thereby verifying that the newly proposed definitions of the structural parameters are reasonable.

In this paper, a new definition of a structural parameter for soil is given to characterize the mechanical properties of soils and their changing patterns. The soil structural parameter is a quantitative descriptor of soil structural properties. Structural parameters are related not only to the grain size, density, and moisture content of the soil material composition and state, but also to the spatial arrangement of soil particles in the soil skeleton structure and the characteristics of intergranular associations. The new definition of the structural parameter, established from the comparison of loess structural stability and variability, is defined as the ratio of the shear strength of undisturbed loess to that of remodeled saturated loess. The patterns of moisture content, confining pressure, and dry density on structural properties were analyzed and the degrees of influence of each factor on structural properties were quantified. By analyzing the change rule of the structural parameter of loess with the difference of moisture content and plastic limit, its change rule with plastic limit and liquid limit, and the change rule of the structural parameter with the liquidity index, the essential relationship between the structural parameter and grain size, density, and moisture is revealed. The essential relationship between the structural parameter and grain size, density, and moisture were also revealed.

Uncompacted saturated loess retains its residual pore structure without artificial compaction, making it highly sensitive to environmental changes such as dehydration-rehydration cycles. This study investigates the dynamic characteristics of uncompacted saturated loess in the Xi'an area, where infrastructure projects are commonly affected by the soil's instability. Dynamic triaxial tests were conducted under varying confining pressures and dehydration-rehydration cycles to examine the dynamic stress-strain relationship, dynamic modulus, and damping ratio variation. The methodology involved multi-stage loading using dynamic triaxial equipment, with cycles of drying and rehydration applied to replicate field conditions. A hyperbolic tangent function was used to model the dynamic stress-strain behavior, and structural parameters m1 and m2 were introduced to quantify the soil's stability and variability. Key findings show that dynamic stress increases with dehydration-rehydration cycles, while dynamic modulus and damping ratio decrease, especially during the initial cycles. The results provide critical insights into the behavior of uncompacted saturated loess under dynamic conditions, offering practical guidelines for managing soil stability in infrastructure projects across the Xi'an region.