Dynamic effect and stress propagation property analysis by transient unloading of a rock sample with high stress

In this paper, the strain rate equation of a rock sample end block unit was obtained during the transient unloading process. The strain rate reached a 101 s-1 magnitude, indicating that the rock sample had an obvious dynamic effect according to the strain rate standard of rock loading dynamics. Moreover, the dynamic module of the 3DEC program and its “static stress initialization-dynamic unloading” calculation mode were used to analyse the stress propagation property in the transient unloading process. It was found that the rock sample with elastic material produced a tensile stress that was reflected at the fixed end and free end, circularly forming high values of tensile stress and compressive stress. The cycle period was 4 × T when the propagation time from the free end to the fixed end was T. On the other hand, a rock sample with elastic-plastic material displayed a plastic damage zone that was affected by tensile stress, which was produced by reflection at the fixed end. Finally, it was found that the inner stress was always tensile stress and that compressive stress never appeared after the damage zone was produced in the circular propagation process.