CHANGE OF MECHANICAL STRENGTH OF LOESS IN ILI REGION UNDER DIFFERENT FREEZE-THAW CYCLES AND MOISTURE CONTENTS

The occurrence of frequent loess landslides during the snowmelt and rainy seasons in the Ili region of Xinjiang necessitates a thorough investigation into the mechanical strength variations of loess in the region under different freeze-thaw cycles and moisture contents. This study focuses on examining the macroscopic and microscopic characteristics of loess at a natural slope in Xinyuan County,Ili region. Through comprehensive laboratory triaxial compression tests and scanning electron microscopy experiments,the following key research findings are obtained:(1)Under different freeze-thaw cycle conditions,the triaxial compression tests reveal a predominant axial deformation process during which the deformation failure mechanism transitions from extrusion-lateral tensile cracking to bending-longitudinal tensile cracking. The cohesion of the samples generally exhibits an initial decrease,followed by an increase and subsequent stabilization,whereas the internal friction angle demonstrates an overall increasing-decreasing trend. (2)Moisture content significantly influences the degree of hardening-softening of the yellow loess samples. Increasing moisture content leads to a gradual transformation from weak softening to weak hardening,followed by general hardening,and finally,a return to weak softening. The cohesion and internal friction angle of the samples exhibit a quadratic relationship with moisture content,displaying an initial increase and subsequent decrease. (3)The microstructure of the loess undergoes a transformation from a granular,intercalated,and face-cemented to a micro-cemented structure under different freeze-thaw cycle conditions,evolving further into a blocky,dispersed,and point contact-cemented structure. The coalescence of smaller particles results in the formation of larger particles,leading to a complex particle morphology with reduced equiaxed particles and disordered arrangements. Continuous fracturing of the yellow loess particles contributes to pore filling,pore coalescence,and simplified pore morphology. Overall,the micro-particle structure of the loess in the Ili region experiences a stable-unstable-stable process. (4)With increasing moisture content,the microstructure of the yellow loess exhibits a transition from a granular,intercalated,and face-cemented to a micro-cemented structure. The optimal moisture content represents a critical point for the loess in the Ili region,characterized by the highest proportion of large particles,equiaxed particles,the simplest contour lines,and the most ordered particle arrangement. These research findings provide a robust theoretical foundation for the prediction and prevention of loess landslide disasters in the Ili region.