An Experimental Study on the Expansion Rate of Blasting Cracks in Prefabricated Grooved Concrete Under Vertical Stresses

With the advancement of deep engineering (e.g., deep resource development, tunnel excavation), the deep rock mass is in a high in situ stress environment, leading to a critical engineering challenge: traditional blasting often causes disordered blast-induced crack propagation (severe deviation from the target direction) and unstable expansion rates, which reduce the directional blasting efficiency, trigger over-excavation/under-excavation, and threaten construction safety. Water jet notching is a promising directional control technique, but its coupling effect with vertical stress (a dominant component of in situ stress) on blasting crack characteristics remains unclear—hindering its application in deep engineering. To address this problem, reveal the law of blasting crack expansion in deep rock, explore the mechanism of controlled blasting for deep rock fractures, and clarify the effect of deep environmental water jet notching on the blasting effect, this study carried out experimental research on the crack extension velocity of the directional blasting of prefabricated grooved concrete under vertical stress (based on the crack extension strain gauge test system and perimeter pressure loading system) and verified the results by numerical simulations. The main conclusions are as follows: (1) Within the experimental test range, with the increase in vertical stress, the deviation of cracks from the prefabricated groove center in the vertical direction gradually decreases, indicating that vertical stress can further guide the direction of the crack extension on the basis of prefabricated grooves. (2) The experimentally measured crack expansion velocity shows a decreasing trend with the increase in the crack expansion length; the average crack expansion velocity is enhanced with the increase in vertical stress, while the change in the crack tip velocity is suppressed as a whole and gradually tends to be flat at approximately 555.6 m/s. (3) Numerical simulation results (using a model replicating the experimental concrete specimens) further verify the accuracy of the experimental results: the increase in vertical stress further guides the vertical crack expansion, enhances the average crack expansion velocity, and slows down the decay of the crack extension velocity. The core value of this research lies in “converting theoretical experimental data into engineering control capabilities.” Its findings can be directly applied to key areas such as deep resource development, tunnel engineering, and water conservancy projects. While ensuring engineering safety, improving efficiency, and reducing costs, it also provides scientific support for engineering construction in complex geological conditions.