Mechanical properties and two damage models of frozen-thawed rocks under triaxial compression

Freeze-thaw induced damage in rock engineering is common in cold regions. However, a damage model for capturing the whole failure process of frozen-thawed rocks is still lacking. In this paper, triaxial compression tests of red sandstone experienced with different freeze-thaw cycles (FTCs) were conducted. Subsequently, the variation of mechanical properties with the numbers of FTCs under different confining pressures were obtained, including peak deviator stress, peak strain, linear elastic modulus, residual strength, friction angle and cohesion. The completely compacted point on stress-strain curve of rock was determined by calculating the strain difference between the stress-strain curve and a reference line. On theses bases, two damage constitutive models considering the initial compaction phase and residual deformation phase were established by means of the continuum damage mechanics and statistical microelement strength theory together with the random exponential function of strain difference. The calculated data obtained from the two proposed models and measured data were then compared. The results shows that the proposed model I is suitable for all rocks samples experienced with FTCs, while the proposed model II is suitable for rocks with small residual strength or large stress difference between peak strength and residual strength. Meanwhile, the two proposed models were compared with the existing ones by evaluating the factor omega . The influence of confining pressure and FTCs on damage evolution of rock was discussed, and the physical meanings of the parameters in the two models were analyzed in details. The findings are beneficial for providing a reference in developing a constitutive damage model for rocks in cold regions.