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

• A new nonexplosive shaped-excavation method for tunnel peripheral holes is studied. • The mechanism of directional rock failure under IESF is investigated. • The progressive rock failures of tunnel peripheral holes are displayed. • IESF shows superior directional rock failure capability compared to CB and SCB. • The numerical results are verified by comparing with the field test results. Due to the detrimental effects of detonation waves on the stability of surrounding rock, non-explosive 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 shaped-excavation of tunnel peripheral holes. [ABSTRACT FROM AUTHOR]