Study on vibration characteristics of roadheader cutting pre-cracked hard rock

To address severe equipment vibration and large load fluctuations during hard-rock excavation, this study proposes mechanical pre-cracking as a preparatory treatment. A hard-rock model containing pre-cracked holes is developed using the discrete element method; the crack initiation and propagation induced by a hydraulic cracker are simulated. The rock models before and after pre-cracking and a rigid-flexible coupling model of the roadheader are then analysed jointly via DEM-MFBD two-way coupling, and the cutting loads and vibration responses are systematically examined. Results indicate that the three-way average load on the cutting head is reduced by 8.2% and the load fluctuation coefficient decreases from 0.0242 to 0.0213 following rock pre-cracking, effectively mitigating impact loads. Frequency-domain analysis shows that, within the principal vibration band of 20-30 Hz, the vibration-acceleration amplitudes of the cutting head, cutting arm and slewing table are reduced by 14.7%, 8.7% and 3.6%, respectively, demonstrating a "near-loaded component" vibration response. This reveals an attenuation law along the transmission path: components closer to the load exhibit superior vibration damping compared with remote elements. The study confirms that mechanical pre-cracking achieves effective vibration attenuation at the source by reducing the overall stiffness of the rock mass and altering the rock-breaking pattern, thereby providing a theoretical basis and engineering reference for improving the efficiency and reliability of hard-rock tunnelling equipment.