Experimental study of nonlinear damping characteristics on granite and red sandstone under the multi-level cyclic loading-unloading triaxial compression

Damping is an important dynamic characteristic of rock masses and has an important impact on seismic engineering. In this paper, a multi-level cyclic loading-unloading triaxial compression experiment was conducted on granite and red sandstone under different confining pressures with two stress paths: one with different amplitudes and the other with the same amplitude. The effects of the two stress paths on the damping ratio, damping coefficient, and elastic modulus evolution characteristics under different confining pressures were studied. The damping parameters and dynamic elastic modulus of the two types of rock under different confining pressures were calculated, and the variation in the damping parameters with the stress level and strain level was determined. The linear interrelation of the damping ratio, damping coefficient, and dynamic elastic modulus was explored. The results show that the damping coefficients of the red sandstone and granite can be expressed as a linear function of the dynamic elastic modulus. The dynamic elastic moduli of the red sandstone and granite increased with increasing strain ratios and stress ratios. Under the variable-amplitude stress path, the dynamic elastic modulus growth rate of the red sandstone was approximately 60% of that of the granite. Under the fixed-amplitude stress path, the dynamic elastic modulus growth rate of the red sandstone was approximately 20% of that of the granite.