Failure mechanism and lessons from two-wing polycrystalline diamond compact drill bit drilling in coal roadways.

• The failure characteristics of boreholes under different drilling modes are revealed. • A novel experimental system for measuring rock properties during drilling is developed. • A cutting mechanics model is established to analyze the failure mechanisms in drilling. Drilling failure is a key factor limiting the effectiveness of surrounding rock identification during coal roadway drilling. While most studies focus on the failure mechanisms of large-scale drilling projects, limited attention has been given to small-sized drill bits, such as rock bolt drill bits. This study, based on the use of a two-wing polycrystalline diamond compact (PDC) drill bit in coal roadways, developed a novel experimental system to detect rock mass properties during drilling. Drilling tests were conducted on specimens with varying uniaxial compressive strengths to analyze the failure characteristics under F t - n and V - n drilling modes, revealing the underlying failure mechanisms of PDC bolt drilling in coal roadways. The results show that in the F t - n mode, higher rotational speed and thrust increase the likelihood of failure, particularly in rocks with lower uniaxial compressive strength. Failure is preceded by a gradual reduction in drilling speed and an increase in torque, driven by reduced rock-breaking energy and increased friction energy. In the V - n mode, higher drilling speed combined with lower rotational speed makes rocks with higher uniaxial compressive strength more susceptible to failure. In this case, failure is indicated by a sharp increase in thrust and torque, leading to friction energy buildup. Additionally, the reliability of the findings was validated through chip particle size distribution and cutting depth measurements. This study provides new insights into the failure behavior of small-diameter PDC bits, with implications for both engineering applications and future research directions. [ABSTRACT FROM AUTHOR]