Abstract: The triaxial cyclic loading and unloading is conducted on the coal sample through RMT-150B rock mechanics testing system. The deformation and strength characteristics of the coal samples during the tests are analyzed. The results show that during the tri-axial cyclic loading the coal sample deformation shows distinct memory and good fitting in stress-strain curve between the cyclic loading and the continuous loading. For loading and unloading prior to yield, the elastic modulus of loading procedure is always lower than the elastic modulus of unloading procedure. And the elastic modulus increased slightly with the frequency. The elastic modulus of unloading procedure after peak value is lower than that before peak value; however, the elastic modulus is still higher than that of first loading procedure. The peak strength and residual strength are proportional to the confining pressure during triaxial compressive test, which is consistent with the Coulomb strength criterion. The friction factor obtained from the regression analyses of the peak strength, residual strength and confining pressure are roughly equal and the cohesion is reduced by 54.4%.

Key words: rock mechanics, triaxial compression, cyclic loading, deformation characteristics, strength characteristics