Improvement of Structural Parameters of Loess and Its Relationship with Strength Indicators

This paper derives and modifies the structural quantitative indicator of loess—the structural index—based on the theory of limit equilibrium, thereby obtaining structural evolution parameters and structural modification parameters. However, since the structural index is defined for uniaxial stress states, this paper also introduces a structural parameter applicable to complex stress states—the complex stress structural parameter mτ. This parameter is not only applicable to complex stress states, but also enables the study of soils such as soft clay that are difficult to test under uniaxial compression. Additionally, it offers the advantages of requiring less testing effort, featuring simpler expression formulas, and possessing clearer physical meaning. Finally, the relationship between complex stress structure parameters and soil strength indicators was analyzed. We defined a quantitative indicator—the comprehensive structural state parameter Pcs—that reflects the combined effects of soil structural factors. By combining comprehensive structural state parameters with the physical properties of undisturbed loess (such as moisture content and dry density), it is possible to determine the strength parameters of loess under a given structural state over a wide range.