Crack Propagation Behavior and Damage Extent of Rock Mass under Instantaneous Expansion in Borehole

Roof-cutting blasting by explosives involves certain operational risks and is prone to cause damage to surrounding rock. Accordingly, a new non-explosive directional rock-breaking technology called Instantaneous Expansion with a Single Fracture (IESF) has been developed. This paper focuses on the research of the crack propagation behavior and damage extent of rock mass under the action of IESF. Firstly, the directional rock-breaking principle of IESF is analyzed, and the theoretical radius of the crushed zone ( R_c ) and fracture zone ( R_f ) for conventional blasting (CB), shaped-charge blasting (SCB), and IESF under cylindrical charge conditions are derived. Subsequently, a field comparative experiment of the three methods was conducted. The results showed that CB produced cracks in random orientations around the hole wall, SCB produced secondary cracks in addition to two primary cracks in splitting direction, and the cracks produced by CB and SCB contain both Mode I and Mode II. Conversely, IESF only produces Mode I cracks in the presplitting direction. Finally, R_c and R_f of the three numerical models considering the rock mass heterogeneity were statistically analyzed, the results demonstrate that R_c (IESF) < R_c (SCB) < R_c (CB), while R_f (IESF) > R_f (SCB) > R_f (CB). The statistical analysis of the monitoring point pressure and Young's modulus during the damage process further verified the directional rock-breaking mechanism of IESF. The research results have improved the theoretical system of IESF and contributed to the promotion and application of IESF technology.