Abstract: Cyclic impact tests on sandstone under different axial and confining pressures are conducted with a modified three-dimensional split Hopkinson pressure bar (SHPB). The main research contents are change property of energy absorption per unit volume, relationship between energy absorption per unit volume and average strain rate, effects of axial compression and confining pressure on energy dissipation of sandstone under cyclic impact loads. Confining pressures are set as 4, 8, 10 and 12 MPa; and four levels of axial stresses are 49, 84, 105 and 125 MPa respectively. Incident waves in input bar are approximately equal and incident energy is equal to 230 J. The results show that energy absorption per unit volume increases with the increasing number of cyclic impacts, when the cyclic impact loadings are a constant. Energy absorption per unit volume has a good linear increasing relationship with average strain rate. The linear-fitted slope K of average strain rate and energy absorption per unit volume indicates a trend of “increase, constant, then decrease” with the increasing axial stress. When the axial stress is smaller, K increases and then becomes lower with the increasing of confining pressure. The smaller axial stress is, the bigger the confining pressure corresponding to slope’s turning point is. After the axial stress reaches to 125 MPa, K continually reduces with the increase of confining pressure. The conclusions may provide the theoretical basis for blasting design of rock mass engineering under different in-situ stress conditions.

Key words: cyclic impact, axial compression, confining pressure, energy dissipation, effect