Effect of freeze-thaw cycles in mechanical behaviors of frozen loess

A series of triaxial compression, creep and stress relaxation tests at temperature of − 6 °C were conducted on frozen loess, experienced different freeze-thaw numbers (0-12times), in order to study the thermal cycling effect in mechanical behaviors. The freeze-thaw process has a strong influence in the mechanical behaviors of frozen loess. The strength, stiffness and viscosity properties of frozen loess weaken gradually with the increase of the freeze-thaw procedure until the cycle number gets to the critical value for steady state of soil sample. The freezing low temperature ranged from − 6 °C to − 12 °C has no evident effect in the testing results of same freeze-thaw numbers. The strength distribution loci of frozen loess in the equivalent stress-mean stress space exhibits a unidirectional shrinkage over the range of the freeze-thaw process studied. Triaxial strength characteristics of frozen loess, experienced different freeze-thaw numbers, are more in agreement with the Ma's failure criterion for frozen soils (Ma et al., 1993). The stiffness properties (elastic modulus, elastoplastic coupled degree and damage degree) and the viscosity properties (relaxing stress, stable relaxation time, stable creep rate and viscoelastic modulus) of frozen loess both depend on the freeze-thaw process. The microstructure change of frozen loess induced by the thermal cycling effect is analyzed detailly so as to explore the micro-mechanism of property degeneration. Finally, a developed constitutive model, considering the freeze-thaw and confining pressure effect, is proposed to research and predict the triaxial strength and deformation characteristics of frozen loess experienced different thermal cycling process.