Effects of Alhagi sparsifolia root content and soil moisture content on soil deformation and strength under different freeze-thaw temperature conditions

This study focuses on cold arid regions in Xinjiang, China, and investigates the reinforcement effect of Alhagi sparsifolia roots on sandy soil under freeze-thaw conditions. Freeze-thaw cycle and direct shear tests, combined with environmental scanning electron microscopy (ESEM), were conducted to analyze the effects of root reinforcement on the deformation and strength characteristics of sandy soil under varying soil water contents (8–14 %) and freezing temperatures (−5 to −20 ℃). The results revealed that soil deformation during freeze-thaw cycle underwent five distinct stages and was strongly controlled by soil water content and temperature. Root incorporation reduced the maximum soil deformation by more than 30 %, and the suppressive effect exceeded 51 % at high soil water content (14 %). In low-water-content soils (8 %), excessive root content (>0.35 %) induced deformation rebound, which was attributed to root clustering and the development of interfacial voids. At the optimal root content (0.28–0.35 %), the maximum shear stress of the root-soil composite increased by 5–45 %, with the specific magnitude depending on soil water content and freezing temperature. Moreover, the optimal root content (η) decreased with increasing soil water content. The results demonstrate the effectiveness of A. sparsifolia in enhancing soil stability under freeze-thaw conditions and highlight the nonlinear and moisture-sensitive characteristics of root reinforcement. This study provides a theoretical basis for optimizing vegetation-based slope stabilization strategies in cold arid environments. • The freeze-thaw deformation process of sandy soil was divided into five distinct stages. • An optimal root content (η = 0.28∼0.35 %) simultaneously minimized deformation and Maximized shear strength. • The deformation rebound at high root content was explained by root clustering effects and interfacial voids. • ESEM observations confirmed the root–soil interaction mechanism under freeze–thaw conditions.