Dynamic Behavior of Lignin Fiber-Stabilized Loess Subjected to Freeze–Thaw Cycles through Resonant Column Testing

Lignin fiber (LF), derived from wood, is a green solution for reinforcing soils. Although the behavior of LF-stabilized loess under static loading has been well studied, its response to repeated loading, such as cyclic freeze–thaw (F–T) and seismic loading, warrants further investigation. This study conducted a series of resonant column tests on LF-stabilized loess, considering the effects of LF content, F–T cycles, and confining stress. Test data were interpreted using three dynamic models for clayey soils, and microscopic tests were conducted to understand the reinforcing mechanisms. Results showed that increasing the LF dosage improved dynamic shear modulus up to 3% LF content but reduced it beyond that. The dynamic shear modulus generally decreased with F–T cycles, with the most significant drop after the second cycle. Increasing the confining stress resulted in a linear increase in dynamic modulus. Conversely, the damping ratio showed opposite trends compared to the dynamic shear modulus. Among the three dynamic models examined, the Stokoe model best described the dynamic responses. Based on the microscopic analysis, the dynamic responses of loess specimens prepared to the same dry density were affected by the combined effects of increasing fiber reinforcement and increasing pore space as LF content increased.