Study on mechanical properties of roadheader’s picks when cutting pressure-relief rocks

With the deepening of coal mining, borehole unloading has become the main measure to improve the efficiency of deep rock excavation under high in-situ stress, which can effectively reduce the stress of surrounding rock and improve the excavation efficiency. After borehole unloading, the rock produces stress transfer, strength deterioration and non-linear distribution inside the rock mass, resulting in changes in the excavation characteristics of the rock mass. In order to ensure the rapid and efficient excavation of the unloaded rock in the borehole, ABAQUS finite element analysis software has been used to study the influence of different parameters on the excavation efficiency of the unloaded rock in the borehole. The results show that under the working conditions of 50 MPa in-situ stress, cutting angle of 30°, the pick is continuously affected by high ground stress, and the force is large, which is not suitable for excavation of unloading rock; when the cutting angle is 45° and 60°, the three-directional force of the pick is significantly decreased, and with the change of cutting parameters, the rate of force change of the cutting teeth is between 8% and 54%, indicating that the ratio of cutting parameters had a great impact on the mechanical properties of the pick. The optimal tunneling parameters are cutting angle of 60°, cutting speed of 2 m/s, cutting depth of 0.075 m. In the multi-tooth simulation, when the spacing between the cutting teeth is 0.075 m, the force on the cutting teeth is the minimum, and the maximum characteristic values of the multi-tooth synchronous cutting teeth in X and Z directions are smaller than the stress characteristic values of the asynchronous cutting teeth, and the driving efficiency of synchronous cutting is higher than that of asynchronous cutting. The above research results can effectively reduce the difficulty of rock crushing under high ground stress unloading and improve the tunneling efficiency.