Anisotropy and microscopic mechanism of lignin-modified loess

In recent years, calcium lignosulfonate, an environmentally friendly additive, has been widely applied in the field of loess reinforcement. However, research on the anisotropic behavior of lignosulfonate-modified loess under complex stress conditions remains limited. This study employs hollow cylindrical torsional shear tests to investigate the effects of calcium lignosulfonate on the anisotropic properties of loess. Additionally, microstructural mechanisms were explored using scanning electron microscopy (SEM), mercury intrusion porosimetry (MIP), and X-ray diffraction (XRD) analyses. The results indicate that lignosulfonate significantly enhances the failure strength of loess, with the modified loess exhibiting superior strength and plasticity compared to remolded loess. Microstructural analysis reveals that lignosulfonate improves particle bonding and stability by filling voids, forming "molecular bridges", and creating a three-dimensional network structure. The active functional groups of lignosulfonate interact with loess particles through ion exchange and chemical bonding, leading to reduced particle spacing and a thinner double electric layer. Furthermore, the particle orientation in lignosulfonate-modified loess becomes more uniform, effectively mitigating soil anisotropy. This study identifies the optimal calcium lignosulfonate content in loess as 1%, providing theoretical support for roadbed engineering and other construction projects under complex stress conditions in the Xining loess region of Qinghai Province.