Experimental study on dynamic fatigue properties of dolomite samples under triaxial multilevel cyclic loading

In an earthquake, the initiation, movement, and deposit characteristics of a rockslide are closely related to the dynamic responses of rock masses, which constitute slope materials. In this study, considering time-varying amplitudes of earthquake wave, dolomite samples collected from the source area of Donghekou rockslide, triggered by the 2008 Wenchuan earthquake, were tested under triaxial multilevel cyclic loading to investigate the dynamic fatigue properties. For three samples considered herein, cyclic loadings reduced the fatigue strength by 33.1%, 29.8%, and 39.9% in comparison with static compressive strength. Based on the hysteresis loops of the axial stress–strain curve, cumulative residual strain, dynamic elastic modulus, dynamic damping ratio, and damping coefficient were obtained, and their response to increasing number of cycles or stress amplitude revealed a significant three-phase evolution process for the fatigue behavior of dolomite subjected to multilevel cyclic loading. At each level of cyclic loading, the cracks and pores generated in the prior level of loading were closed, which resulted in the recovery of the stiffness of the rock sample in the initial period, thereby causing the dynamic damping to initially decrease and then increase. In the last phase before failure, a sharp increase was observed in the cumulative residual strain, whereas a significant decrease was observed in the dynamic elastic modulus, indicating severe unrecoverable damage in rock samples. Compared with the fatigue failure mode under static loading, cyclic loading resulted in an extremely rough shear surface, with shearing powders in the shear zone and local crushing at the two ends of the shearing surface. The generation of shear surfaces was significantly influenced by the development of pre-existing quartz veins in rock samples.