Impact Fracture Characteristics of Red Sandstone with Varying Moisture Contents under Biaxial Static Compressive Stress

This study explores the dynamic fracture behavior of red sandstone under varying moisture contents. Dynamic impact tests were conducted using a true triaxial Hopkinson pressure bar system under combined axial and lateral confining pressures, aiming to characterize the fracture behavior of red sandstone under dynamic loading. The experimental matrix included five distinct moisture content levels and five lateral confining pressure levels. The effects of moisture content and lateral confining pressure on dynamic fracture behavior were assessed via dynamic parameters, energy distribution analysis, and fractal dimension quantification. The results indicate that lateral confining pressure increases the dynamic elastic modulus and peak stress of red sandstone, whereas increasing moisture content leads to an overall reduction in strength-related parameters and an increase in failure strain. As stress levels or moisture conditions increase, the sensitivity of these dynamic parameters gradually weakens, exhibiting a clear diminishing marginal effect. Energy analysis shows that lateral confinement promotes energy transmission while suppressing energy reflection and dissipation. In contrast, increasing moisture content tends to enhance energy reflection and reduce transmitted energy, with the dissipation behavior exhibiting a quadratic trend. Fragmentation analysis shows that lateral confinement effectively suppresses dynamic fracture in red sandstone. Meanwhile, the influence of moisture content on fragment size distribution depends on the level of lateral stress, leading to distinct evolutionary patterns under different confinement conditions.