Analysis of unloading failure mechanical characteristics in columnar jointed rock mass

This study fabricated columnar jointed rock mass specimens with varying joint inclination angles using rock-like materials and conducted triaxial unloading tests under different initial confining pressures and unloading rates to investigate their mechanical characteristics under various conditions. The results indicate: (1) As the initial confining pressure increases, the peak strength of the specimens gradually rises, and the elastic modulus progressively increases. With increasing joint inclination angle, both the peak strength and elastic modulus of the specimens exhibit a "U"-shaped trend, initially decreasing and then increasing. (2) Under triaxial unloading conditions, the stress–strain curve of columnar jointed rock mass shows an inflection point at the unloading stage, where the elastic modulus suddenly increases, and the specimen volume transitions from compression to expansion. The strength of columnar jointed rock mass under triaxial unloading conditions is lower than that under conventional triaxial compression conditions. Moreover, as the unloading rate increases, the specimen strength gradually decreases, and the characteristics of brittle failure become more pronounced.