Investigation of mechanical and ultrasonic properties of sandstone with different flaws characteristics under triaxial stress

This study investigates the impact of flaw angle and length on the mechanical properties and ultrasonic wave velocity of sandstone under triaxial stress. Sandstone specimens with different flaw angles (0°, 30°, 60°, 90°) and varying flaw lengths (10 mm, 15 mm, 20 mm, 25 mm) underwent comprehensive examination through conventional triaxial compression tests and ultrasonic monitoring systems. The experimental results indicate that flaw angle and length significantly affect the sandstone’s mechanical properties and ultrasonic velocity. As the flaw angle increases, both the peak stress and elastic modulus of sandstone demonstrate an upward trend. Conversely, increasing flaw length diminishes the sandstone’s mechanical strength and structural integrity. Particularly noteworthy is the observation that when the flaw length exceeds 20 mm, the unstable expansion of cracks significantly escalates, resulting in sandstone fracture at lower stress levels. The variation of longitudinal wave velocity reflected the failure process and crack evolution characteristics of sandstone. The wave velocity initially shows a temporary increase followed by a continuous decrease, with the turning point occurring near the crack closure stress. In contrast, the evolution of crack width is observed to follow the opposite pattern. This study provides new insights into the impact of flaw characteristics on the mechanical and ultrasonic properties of sandstone, offering valuable guidance for geological engineering design, rock stability assessment, and coal mining operations.