Stress ratio sensitivity—a novel parameter for evaluating the shearing-based structural characteristic of loess

The structural characteristics of the soil dominate macro-mechanical behaviors. The features of loess in geological engineering contexts are related to its structural properties. Hence, quantitative studies of loess’ structural properties have been widely undertaken. In this study, a novel structural parameter—stress ratio sensitivity (S_η)—has been proposed, based on the concept of mechanical sensitivity by considering the stress ratio characteristics of undisturbed and remolded loess. The rationality of the S_η parameter was validated via the performance of triaxial shear tests on samples with different water contents. The results suggest that the value of S_η decreases first and then stabilizes as the strain increases, and here, its value converged towards, but was always larger than 1. The S_η–strain curves herein can be divided into three stages: rapidly decreasing, slowly decreasing, and stable state. A higher water content in the sample corresponds to a lower rate of decrease in S_η. Furthermore, the initial value of the structural parameter (S_ηo) was obtained via the fitting of data onto the rapidly decreasing stage of the S_η–strain curves, which could be referred to evaluate the initial structural state of loess. Increasing confining pressure and water content reduced both the S_η and S_ηo values significantly. Variations in loess’ structural properties have been attributed to changes in cohesion, whose difference reflected the loss in structural property due to remolding compared with the original. As the cohesion difference (∆\({c}^{\prime}\)) increases, the value of the S_ηo increases exponentially. The S_η can reasonably describe the evolution of loess’ structural properties under different loading conditions, and provide a new idea for quantitatively illustrating the relationship between the structural characteristics and macro-mechanical behavior of loess.