Experimental study on dynamic impact characteristics of sandstone subjected to freeze-thaw cycles

ObjectiveThis study aims to investigate the effects of freeze-thaw cycles on the dynamic mechanical properties and microstructural characteristics of sandstone. MethodsDynamic impact compression tests, nuclear magnetic resonance (NMR) detection, and scanning electron microscopy (SEM) observations were conducted on sandstone samples subjected to 0, 30, 60, 90, and 120 freeze-thaw cycles, with impact velocities set at 3, 6, and 9 m/s respectively. ResultsThe results indicate that the dynamic impact failure mode of freeze-thawed sandstone is overall crushing failure. As the number of freeze-thaw cycles and impact velocity increase, the fragmentation degree of sandstone intensifies, characterized by reduced fragment size, increased number of fragments and proportion of powder, and elevated fractal dimension. Under the same impact velocity, the dynamic mechanical properties of sandstone continuously deteriorate with the increase in freeze-thaw cycles, and all dynamic mechanical performance indicators exhibit rate-dependent effects. Additionally, an exponential attenuation model for the dynamic peak stress of freeze-thawed sandstone was established, which proves that impact velocity can partially compensate for the damage and deterioration caused by freeze-thaw cycles, resulting in a smaller attenuation constant and a delayed half-life. The established fractal dimension-dynamic strength evolution equation enables the fractal dimension to not only quantitatively describe the fragmentation degree of sandstone after impact failure but also further predict its dynamic strength. With the increase in freeze-thaw cycles, the size and number of pores and cracks inside the sandstone increase, and the degree of structural damage aggravates. Based on the above results, the damage and failure mechanism of sandstone under freeze-thaw cycles was explored, revealing that the freeze-thaw damage of sandstone is the result of the combined action of multiple factors. ConclusionThis study can provide relevant references for rock engineering in cold regions.