Abstract: In seismic events, the occurrence of a rock landslide strongly depends on the dynamic mechanical properties of the rock mass materials of slope. In order to understand the characteristics of rock material under dynamic load, this study took phyllite, a representative rock mass developed in the Donghekou landslide area triggered by the Wenchuan earthquake in 2008, as the research object, to conduct a multi-stage cyclic loading and unloading test under triaxial compression. The confining pressure was 10 MPa, the loading frequency was 2 Hz, the loading waveform was sine wave, and 60 cycles were loaded at each level of stress. According to the axial stress-strain curve, the effects of cycle number and upper limit stress on elastic modulus, damping parameters and residual strain of phyllite samples were analyzed, and the evolution law of dissipated energy was also studied. The results are shown as follows: (1) The elastic modulus, damping ratio and damping coefficient of the samples decreased as the cycle number increased. When the upper limit stress was low, the internal structure of rock began to change significantly due to the closure of initial cracks and pores and formation of small new cracks, which caused the values of the parameters fluctuated greatly with a general increase as the cycle number increased. When the upper limit stress was high, the parameters demonstrated a slight change. (2) The cumulative residual strain showed an increasing trend as the cycle number and stress level increased, which was mainly related to the stress increase process (ramp loading stage) of rock samples. However, the relationship between the cumulative residual strain and the upper limit stress of rock samples at one stress level (cyclic loading stage) showed a W-type change. (3) The dissipated energy per unit volume also showed an overall increasing trend with the increase in cycle number and stress level. However, at lower upper limit stress level, the energy dissipation per unit volume changed slightly with the increase of cycles; at higher upper limit stress level, the energy dissipation increased in an “L” shape while in a “U” shape near failure. The research results can help to understand the mechanical behaviors of rock under dynamic cyclic loading, as well as to provide theoretical support for the formation mechanism analysis of large rock landslides under earthquake action from the perspective of rock mechanics in future work.

Key words: multi-stage cyclic loading and unloading, elastic modulus, damping ratio, damping coefficient, residual strain, dissipated energy