Damage characteristics of mudstone in loosening blasting: an HJC model-based study

To address the support challenges of deep high-stress roadways in coal mines, this study investigates fracture propagation in floor mudstone from the Shanxi Gucheng Coal Mine using the Holmquist-Johnson-Cook constitutive model. Based on laboratory mechanical tests and theoretical calculations, a comprehensive set of HJC model parameters for mudstone was systematically determined. A two-dimensional radial decoupled charge model was developed in LS-DYNA using an Arbitrary Lagrangian-Eulerian fluid-solid coupling algorithm to simulate the loosening blasting process. The results indicate that while the original HJC model's damage variable effectively captures the formation of the crushed zone, it severely underestimates tensile crack extension, predicting a maximum crack length of merely 25.5 cm. To overcome this limitation, the model was optimized by incorporating supplemental failure criteria for shear strain and tensile stress. The enhanced model successfully reproduced the entire radial fracture propagation process, capturing an extensive fractured zone radius of 205 cm. Crucially, field borehole peeping verified these findings, revealing macroscopic radial fractures extending approximately 1.9 m, which is basically consistent with the simulation results. This study accurately elucidates the dynamic damage mechanisms of mudstone and provides a robust theoretical basis for engineering parameter designs, such as the 4 m borehole row spacing implemented for effective floor pressure-relief blasting.