Mechanisms of rock cutting,breaking,and strength perception of PDC bolt bits in coal mine roadways

ZHANG Nong; GUO Feng; XIE Zhengzheng; WEI Qun; WANG Peng; WANG Jiale; CHEN Ruiji

doi:10.13247/j.cnki.jcumt.20240564

Abstract：Transparent visualization of surrounding rock structures is a crucial prerequisite for intelligent tunneling.However,the current perception accuracy of undulating changes in coal roadway surrounding rocks remains low,primarily due to unclear principles of rock identifica-tion during drilling,significant limitations in field applications and the poor adaptability of drilling parameters to rock properties.Through theoretical analysis and laboratory experi-ments,a planar cutting force model for PDC bolt bits was developed,clarifying the evolution of drilling parameters and the failure characteristics under various drilling modes.The results show that,firstly,based on the optimization of the contact surface types between the cutting teeth and the rock during the drilling process,three theoretical relationships between drilling parameters and rock uniaxial compressive strength were successfully established.This indi-rectly indicates that maintaining certain drilling parameters constant is the optimal path to a-chieving real-time rock strength perception during drilling.Secondly,a new real-time detection system for rock properties during drilling was developed.This system achieves a high level of simulation of the coal roadway hydraulic anchor drill machine's working conditions in terms of drilling posture,confining pressure application,drill rig power,and other aspects.It is e-quipped with two automatic drilling control modes and high-frequency data acquisition func-tions.Subsequently,drilling experiments were conducted under different drilling modes.In the V-n mode,thrust and torque were found to be highly sensitive to changes in drilling pa-rameters and rock strength,and both can serve as primary parameters for identifying rock strength.Drilling failure typically occurred in cases with high drilling speed and low rotational speed,and the probability of failure increased with the rock strength.In the Ft-n mode,only drilling speed showed a sensitivity to rock strength,with drilling failure typically occurring in cases with high thrust and rotational speed,and low rock strength.Finally,the conventional drilling data was substituted into the theoretical relationship for real-time rock strength percep-tion,yielding an average prediction error rate of 10.51％for rock uniaxial compressive strength.The total energy consumed in rock breaking and friction exceeded the cutting input energy,which was identified as the direct cause of drilling failure.The above findings provide theoretical and technical references for intelligent perception applications in coal mine roadway surrounding rock changes.