Investigation on directional failure mechanism of tunnel peripheral holes induced by instantaneous expansion

Due to the detrimental effects of detonation waves on the stability of surrounding rock, nonexplosive excavation techniques for tunnel peripheral holes have been developed. One such method is the instantaneous expander with a single fracture (IESF), which utilizes coal gangue and straw as eco-friendly, recycled components. This paper provides theoretical analysis of the directional failure mechanism of tunnel peripheral holes under the action of IESF, as well as numerical evaluation of its performance relative to conventional blasting (CB) and shaped-charge blasting (SCB) techniques, while accounting for rock mass heterogeneity. A damage variable is introduced to describe the progressive rock failure, and finite element simulations are carried out. Results indicate that IESF outperforms CB and SCB in terms of directional rock failure ability and reducing over/under excavation depth. Moreover, IESF offers superior safety and lower cost. This research reveals the directional progressive failure mechanism of tunnel peripheral holes under instantaneous expansion, providing a theoretical basis for the application of IESF in the shapedexcavation of tunnel peripheral holes.