Research on crack propagation characteristics and mechanical mechanism around gas drainage boreholes.

Instability and fracturing around gas drainage boreholes are among the key factors contributing to low extraction efficiency. In this study, pressure-induced failure experiments were conducted on specimens containing boreholes. The Digital Image Correlation (DIC) method was employed to observe the entire process of crack initiation, propagation, and penetration. Deformation parameters of strain field characteristic points were extracted, and the spatial position and initiation time of the crack tip were analyzed using coordinate transformation formulas. The crack propagation mechanism was further elucidated based on the cohesive zone model. The results show that tensile microcracks appeared at the top and bottom edges around the borehole at 372s, and tangential displacement separation occurred at the left and right sides at 420s, almost simultaneously with tensile failure at the distal end. As loading continued, the distal cracks connected with the left and right side cracks, forming a macro-fracture. Before the peak stress reaches 48%, the initial tensile cracks initiate and propagate, with energy dissipation exceeding the elastic energy. In the later stages, the cohesive force c(x) impedes the propagation of the initial cracks. The characteristics of instability and failure in specimens containing boreholes are highly correlated with the propensity for longitudinal and circumferential cracking in the pressurized zones of mine drilling holes. This reveals the nature of delamination and complex fracturing around gas drainage boreholes and provides a valuable reference for studying the crack propagation patterns around gas drainage boreholes.