Research on sandstone blasting damage and fracturing based on nuclear magnetic resonance and micro CT technology

There are many types of rocks and complex distribution of internal pores, which pose challenges for precise blasting of rock layers. Therefore, studying the spatial distribution of pores inside rocks and exploring the mechanisms of pore development and crack propagation under explosive loads is of great significance for fine blasting. This study takes red sandstone as an example and combines nuclear magnetic resonance (NMR) and computed tomography (CT) techniques to investigate the effect of porosity on sandstone fracture under explosive loading. Numerical simulation techniques are used to explore the mechanism of pore damage inside sandstone under explosive loading. The results showed that after the blasting, there was a significant “draw close” phenomenon between peak 1 and peak 2 in the T₂ spectrum, and the signal intensity amplitude of peak 2 was much greater than that of peak 1. Sandstones with higher porosity typically have higher signal intensity amplitudes at peak 1 and peak 2, and exhibit more severe macroscopic fractures within the sandstone. After blasting, the number of pores in sandstone increases, and internal damage gradually shifts from microscopic rupture to macroscopic rupture. As the quality of explosives improves, the average and peak values of T₂ gradually increase, and the differences in average pore size and pore size become more pronounced. The distribution of pores gradually becomes uneven and irregular. Sandstones with higher porosity have faster propagation and attenuation rates of shock waves during blasting, larger pressure peaks, and more frequent propagation and alternation between pores and sandstone skeletons. This makes it easier for the initial pore throat structure to reach the bearing limit, promoting connectivity between sandstone pores.