Energy Evolution Principles of Shock-Wave in Sandstone under Unloading Stress

Excavation process often induces the unloading rock mass to be in different damage stages, thus changing the propagation and attenuation characteristics of shock-wave energy in rock mass. This paper involved an investigation on the energy dissipation principles during unloading stress process. First, the paper presented small disturbance impact tests to acquire shock-wave data using the modified split Hopkinson pressure bar device. Then we discussed the shock-wave characteristics under different unloading stresses, attenuation characteristics of shock-wave energy at distance and its effects on unloading stress on the attenuation characteristics of shock-wave energy. Results showed that the presence or absence of unloading stress in sandstone had significant effect on shock-waveform. The shock-wave energy showed a spatial exponential attenuation characteristic, and the decay coefficient indicated that the variation degree in low unloading stress region was significantly greater than that in high unloading stress region. The unloading stress cut-off point was sigma/sigma(c)= 23.88%. The shock-wave energy at different locations declined with a trend of slight decrease and rapid attenuation, illustrated that the closer the incident end of the sandstone was, the greater the attenuation degree of the shock-wave energy would be. This paper also analyzed the attenuation rate of shock-wave energy and corresponding different sensitivity to unloading stress, showed that the relationship between attenuation rate and unloading stress could be exposed by a composite linear exponential equation. Therefore, the conclusions can provide reference for the attenuation evolution analysis of shock-wave energy in the excavated rock mass.