Dynamic damage laws of sandstone under different water bearing conditions based on nuclear magnetic resonance

To study the dynamic damage characteristics of sandstone under different water bearing conditions, three different kinds of samples with different moisture states (dry, semi-saturated, and saturated) were prepared. The impact damage of the rock was tested using a split Hopkinson pressure bar (SHPB) with four values of low incident energy. The T₂ spectrum curves, porosity, and pore image of the samples were obtained by scanning the samples by nuclear magnetic resonance test. The results show the following:(1) an increase in the impact energy led to increased average strain rate and strength; (2) after impact, the porosity and porosity variation rate of every sample under different water bearing conditions increase with different amounts; (3) compared with the test before impact, T₂ spectrum curve has obvious right movement trend and large pore peaks increase. The greater the impact energy increase, more obvious the large pore peaks increased are; (4) nuclear magnetic resonance images show that the number and size of pores increase, which show the expansion and evolution of pores in the rocks.