Decoupled explosion in an underground opening and dynamic responses of surrounding rock masses and structures and induced ground motions: A FEM-DEM numerical study

Underground explosion during, e.g., blasting excavation, could generate shock waves, which propagate in surrounding rock mass and might result in damage or destruction of surrounding underground and ground structures. Therefore, it is significant to evaluate dynamic response and stability of underground and ground structures during underground explosion. We aim to understand the explosion process, to investigate blast induced shock wave propagation in jointed rock mass and soil cover, and to determine the dynamic response of surrounding structures and ground motions, with the FEM-DEM method. Effects of explosive parameters including loading density, explosive type and explosion location, the shape of explosion chamber, joint parameters including joint stiffness, orientation, spacing and crossing angle, and soil cover thickness and ground locations on dynamic responses, wave attenuation and ground motions were investigated with the verified FEM based code AUTODYN and DEM based code UDEC. Results showed that peak particle velocity (PPV) increases with increasing charge loading density and decreasing scaled distance. PPV on side walls of the adjacent underground opening, in particular, on the side wall close to the explosion, increases with increasing charge loading density and decreasing distance from the explosion chamber. The explosive type, explosion location and explosion chamber shape have great effects on the PPVs of surrounding rock masses, dynamic responses of the adjacent opening and disturbed zone distributions. Joint properties could significantly influence blast-induced wave propagation. PPV increases with increasing joint stiffness or decreasing crossing angle between two joint sets. With increasing joint dip angle, PPV slightly decreases before sharply increasing. With increasing joint spacing, PPV increases before keeping constant. The ground soil cover could greatly attenuate blasting-induced wave, in particular when its thickness exceeded a critical value. The findings in this paper could be significant for blasting design, protective engineering and underground supporting.