Experimental Study on the Triaxial Shear Strength Characteristics of Red Clay Subjected to Artificial Freezing-Thawing Process

In the pursuit of understanding the shear strength variations of red clay in three states, i.e., normal, frozen, and freeze-thaw, during the implementation of the artificial permafrost method, a low-temperature MTS triaxial testing system is utilized. Triaxial shear experiments on remolded red clay are conducted under varying initial moisture levels, freezing temperatures, and confining pressures. The aim is to explore the triaxial shear strength characteristics of red clay in different freeze-thaw states and elucidate the variations in shear strength throughout the entire artificial freeze-thaw process under diverse conditions. The results show that: (1) In the frozen state, stress-strain curves of red clay consistently exhibit strain hardening. With increased confining pressure at normal temperature and post freeze-thaw cycles, stress-strain curves transition from strain softening to strain hardening, particularly evident under a high confining pressure of 800 kPa. (2) In the frozen state, the shear strength, cohesion, and internal friction angle of red clay exhibit an initial increase followed by a decrease with rising moisture content, reaching a peak at 30%. Throughout the process from normal temperature to freezing and then to freeze-thaw, the shear strength of red clay in the frozen state average increase is 10.5 times, while post freeze-thaw shear strength is lower than that at normal temperature. (3) Lower freezing temperatures correspond to higher shear strength in the frozen state of red clay. After freeze-thaw, cohesion, internal friction angle, and shear strength of red clay decrease with decreasing freezing temperatures. The study results can provide theoretical and technical insights for the construction of artificial permafrost in red clay formations.