Quantitative representation of dynamic properties and internal fissure in deep-seated damaged granite

Abstract Understanding the dynamics of damaged rock masses and the evolution of internal fissures is beneficial to deep engineering. This manuscript takes the common granite in deep engineering as the research object. By applying impact loads, three initial damage states of rock samples were created, and Hopkinson impact tests were conducted at four confining pressure levels to analyze the dynamic characteristics of damaged granite. Selected rock samples of one type of damaged granite after impact at different confining pressures for CT scanning tests, and three-dimensional models of the rock samples were constructed using Avizo software to analyze the effect of confining pressure on the evolution of granite fissure patterns and to quantitatively represent the changes in internal fissure and three-dimensional fractal dimension. The results indicate that with increasing damage, the peak stress and peak modulus of the damaged granite decrease, while the peak strain increases. When the initial damage is consistent, all three parameters increase with the rising confining pressure. Confining pressure alters the number and development direction of internal fissures in granite. Higher confining pressure results in fewer fissures, with their development direction shifting more towards the center of the sample and becoming straighter. As confining pressure increases, the overall volume of three-dimensional fissures in the rock sample gradually decreases, the volume and maximum length of through fissures decrease, the proportion of independent fissures increases, and the three-dimensional fractal dimension continuously decreases. This research provides valuable theoretical guidance for supporting and constructing surrounding rock in deep engineering projects.