Study on the Evolution of Dynamic Liquefaction Characteristics in Lignin Fiber-Modified Sandy Soil

To investigate the liquefaction resistance characteristics of lignin fiber-reinforced sandy soil, natural sand from the Tarim Basin in Xinjiang was selected as the research subject. Cyclic triaxial tests were conducted to optimize the fiber content, and a comparative analysis was performed on the liquefaction resistance and dynamic strength indices of pure sand and optimally reinforced sand under varying confining pressures, consolidation ratios, and vibration frequencies. The results demonstrated that at a lignin fiber content of 2%, the pore water pressure growth rate of the specimen decreased, and the liquefaction failure time was prolonged. The "bridge effect" of fibers effectively inhibited particle sliding. When the confining pressure increased (≥ 200 kPa), the fiber reinforcement effect was significantly enhanced, with dynamic strength improving by up to 64%. At higher consolidation ratios ( K _c =1.5 ~ 2.0), the dynamic internal friction angle increased maximally to 32.3°, attributed to stress anisotropy activating the force-transfer pathways within the fiber network. As the vibration frequency increased (0.5 ~ 2.0 Hz), the dynamic internal friction angle decreased by approximately 2.64°~6.18°, indicating that the viscoelastic hysteresis of fibers weakened the reinforcement effect under high-frequency loading. Based on experimental data, a multivariate nonlinear model for the dynamic internal friction angle was established, incorporating fiber content F _c , consolidation ratio K _c , vibration frequency f , and vibration cycles N . The model achieved an R ² of 0.980 and an RMSE of 0.794°, with validation confirming its predictive accuracy within conventional parameter ranges, meeting engineering requirements. The findings provide a theoretical basis for the seismic design of lignin fiber-reinforced sandy soil foundations.