Study on the Strength Characteristics of Frozen Salt-Rich Red Clay

In low-temperature environments, water and sulfates in red clay crystallize into ice and salt crystals, respectively, triggering a synergistic effect of frost heave and salt heave. Saturation and salt content significantly influence the strength and structural evolution of the soil, thereby affecting its bearing capacity and stability. To investigate the shear strength characteristics of salt-rich red clay, in this study, triaxial shear tests were conducted under varying confining pressures, saturation levels, and salt contents. Scanning electron microscopy (SEM) was used to observe and analyze the microstructural evolution, and the entropy-weighted rank-sum ratio (RSR) method was employed to evaluate the overall mechanical performance. The triaxial test results show that the peak strength increases with confining pressure and saturation but decreases obviously with increasing salt content. Higher salt content leads to earlier strain softening and failure becomes more abrupt. Conversely, increasing confining pressure suppresses softening and enhances strength. SEM observations further indicate that salt crystallization promotes particle separation, pore enlargement, microcrack propagation, and loss of interparticle cementation, thereby weakening the postpeak load-bearing skeleton. Consistently, the RSR method analysis assigns the highest weight to residual strength, with a value of 41.1%, indicating that postpeak bearing capacity is the key factor controlling the stability of frozen salt-rich red clay after deformation. In general, excessive salt content not only reduces peak strength but also aggravates microstructural damage, accelerates strain softening, and degrades residual strength.