Dynamic mechanical properties of artificial jointed rock samples subjected to cyclic triaxial loading

The mechanical behavior of artificial jointed rock samples with different joint dip angles was analysed on the basis of the results of cyclic triaxial tests with 1.0 Hz frequency under different stress amplitudes and different confining pressures. It was found that the dynamic strength decreases with increasing joint dip angles and increases with increasing confining pressures. The stress ratio (the ratio of the maximum stress of the cyclic loading to the static triaxial compressive strength) can comprehensively reflect the influences of joint dip angles, confining pressures and stress amplitudes. For all samples with different joint dip angles, confining pressures and stress amplitudes, the number of cycles at failure decreases with increasing stress ratios. And the evolutionary characteristics of the residual axial strain and residual dilatancy with loading cycles, as well as the evolution law of damages, are determined by the stress ratios. As the stress ratio changes, the evolution laws of the residual strain and the damages form three kinds of situations. A damage variable is defined using the sum of absolute values of the volumetric contraction and dilatancy, which can consider the initial fatigue damage of jointed rocks under cyclic loading and reflect laws of the dynamic damage evolution. During each loading cycle, the samples are slightly compacted and then dilate largely in the reloading stage, while dilate slightly and are largely compacted when unloading. The volumetric strain exhibits a series of significant changing rule within a cycle and with the increasing number of cycles, which contributes to reveal the mesoscopic damage mechanism in the cyclic loading condition. Finally, the confining pressure and the joint dip angle strongly influence the dynamic deformation and failure mechanism of jointed rock samples by affecting the generating of the weak zone along the joint plane and the initiation and propagation of micro-cracks.