Abstract: The values of rock dynamic parameters directly influence the results of dynamic calculation in rock structural engineering, which shall be validated with the results obtained from practical engineering projects. As the frequency and amplitude of actual dynamic loading could change within a specific range, a series of cyclic loading and unloading experiments was conducted by considering the variations of these two factors. The effects of these two factors on the dynamic characteristics of sandstone were analysed, such as dynamic stress-strain hysteresis curve, dynamic elastic modulus, damping ratio and damping coefficient. The results showed that the shape of stress-strain hysteresis loop was closely related to the frequency and amplitude of cyclic loading and unloading. It was found that the higher the frequency was, the plumper the hysteresis loop was, and the greater the cyclic loading amplitude was, and the narrower the hysteresis loop was. When the frequency of cyclic loading increased from 0.02 Hz to 1.00 Hz, the damping coefficient of sandstone gradually decreased, whereas the damping ratio and dynamic modulus slowly increased. The varying ranges of damping coefficient and damping ratio were relatively larger, while the growth range of dynamic elastic modulus was smaller. When the stress amplitude of cyclic loading increased from 10 MPa to 35 MPa, the damping ratio of sandstone gradually decreased, whereas the damping coefficient slightly changed and the dynamic elastic modulus slowly increased. However, the effects of stress magnitude on the dynamic elastic modulus were more significant. Therefore, this study can provide useful references for reasonably selecting dynamic parameters of rock mass.

Key words: cyclic loading, frequency, stress amplitude, damping ratio, damping coefficient, dynamic elastic modulus