Abstract: Compared with traditional blasting methods, static cracking is safer and more environmentally friendly and has been widely used in stone quarrying, rock fracturing, and urban building demolition. However, research on its directional fracture performance remain limited. Challenges such as long crack initiation times and poor predictability and controllability of fracture propagation direction persist. To investigate the influence of notch depth on the fracture behavior of specimens under expansive loading, five groups of static cracking tests were conducted on concrete specimens with different notch depths. Acoustic emission (AE), strain monitoring, and digital image correlation (DIC) were combined to examine the effects of notch depth on fracture modes under expansive loading. The evolution of energy characteristics, strain characteristics, and surface strain fields at different failure stages was also analyzed. Two types of cracks were observed during the tests: P-type cracks, which propagated parallel to the slot direction, and T-type cracks, which propagated perpendicular to it. The results show that, compared with circular-hole specimens, double-wing slotted-hole specimens exhibited crack initiation approximately 1 h earlier. In addition, greater notch depths led to earlier crack initiation. As notch depth increased, the final fracture mode gradually shifted from P-P-T-T to P-P, indicating that deeper notches enhanced stress concentration at the slot and thereby suppressed the formation of T-type cracks. In the P-P-T-T and P-P-T fracture modes, the initiation of T-type cracks caused the strain on the corresponding free surface to change from an increasing to a decreasing trend, producing a distinct turning point in the stress state. When P-type cracks initiated, both the AE hit count and cumulative energy increased sharply. Moreover, the AE hit count and cumulative energy were higher in the P-P-T-T and P-P-T fracture modes than in the P-P mode. In addition, the initiation of T-type cracks produced a second peak in the AE hit count.

Key words: static cracking, notch depth, expansion load, fracture mode