Association analysis of pore development characteristic and uniaxial compressive strength property of sandstone under cyclical impact

Three groups of SHPB experiments are designed to study the damage evolution law of sandstone under cyclical impact loadings. In these experiments, different grades of impulsive pressures and times of shock are considered to have some effects on the damage degree evolution of rock. Moreover, the rock samples subjected to different conditions are performed to investigate the nuclear magnetic resonance(NMR) behavior, and the rock porosity, crosswise relaxation time T₂ distribution and nuclear magnetic resonance image (NMRI) are obtained. The results show that: (1) The rock porosity increases with the times of shock under the same impulsive forces. As the times of shock increases, spectral peaks of the small micro-cracks move from left to right and the area of T₂ distribution increases, which means the porosity increases as the small micro-cracks develop into middle-size. The transition rate, small micro-cracks develop to middle-size, increases with the impulsive forces. (2) As the times of shock increases, both the intensity and area of NMRI white spot and the rock porosity are increased. The damage of rock sample gets bigger so that middle and large micro-cracks propagate and coalesce at the end. (3) The relationship between the NMR characteristics and rock mass strength is discussed which conform to exponential distribution. And a prediction mathematical model of uniaxial compressive strength is established based on the NMR results.