Evolution of the Damping Ratio Considering Cyclic Confining Pressure Under Intermittent Cyclic Loading

The damping ratio is essential to conducting dynamic analysis for underground engineering under traffic loading. Variations in the damping ratio are usually studied using cyclic triaxial tests with continuous cyclic loading; however, intermittent loading is observed under traffic loading. Moreover, both the deviator stress and confining pressure vary cyclically. So far, the development of the damping ratio under intermittent cyclic loading with cyclic confining pressure has rarely been studied. Thus, cyclic triaxial tests with continuous and intermittent cyclic loading were conducted. Unlike continuous loading, where the normalized damping ratio progressively decreases, the corresponding variations under intermittent cyclic loading showed a sudden increase in the initial damping ratio at each restart. Critically, the cyclic confining pressure significantly reduced the normalized damping ratio, with greater attenuation under intermittent loading at higher cyclic confining pressures. In addition, an empirical model incorporating these effects for the damping ratio under intermittent cyclic loading was developed.