Experimental and Numerical Investigation of Rock Breaking Performance by Single Impact Hammer Under Saw Blade Pre-slotted Conditions

Efficient hard rock breaking is crucial for inland waterway dredging. However, the water environment affects the crack propagation of rock breaking and the impact energy of hydraulic hammer, which in turn reduces the efficiency of rock breaking. This paper propose a saw blade pre-slotting assisted impact hammer method to enhance the efficiency of hard rock breaking. Based on the method, the effect of pre-slotted free face on rock breaking is first analyzed. Second, the impact hammer rock-breaking process under free face condition is analyzed using the finite–discrete element method (FDEM). Subsequently, orthogonal experimental method is used to study the effect and significance of working condition parameters (impact hammer diameter, sawing depth, free face distance, falling height, and weight block mass) on each index (impact force, crack length, specific energy, and number of impacts). The results show that the free face can reduce the impact force by 15% and significantly reduce the number of impacts, and the damage characteristics include shear damage in the impact crater center and tensile damage around the crater. The overall influence of parameters is sawing depth > free face distance > weight block mass > falling height > impact hammer diameter. The optimal parameter combinations includes impact hammer diameter of 25 mm, sawing depth of 40 mm, free face distance of 30 mm, falling height of 0.82 m, and weight block mass of 60 kg. The results provide ideas and guidance for efficient hard rock dredging.