微差爆破作用下多条定向裂纹扩展行为试验研究OA

Refined delay blasting using digital electronic detonators has been widely used in rock break-ing engineering,where notched borehole could control the direction of explosion-induced crack propa-gation.This study investigates how delay time affects the propagation behavior of multiple directional cracks through dynamic caustics experiment for delay blasting on specimens with multi-directional not-ched boreholes to unveil crack propagation path and mechanical properties of crack tip.Results show that multi-directional notched boreholes could effectively control the direction of crack propagation.In both groups of specimens,the main cracks generated by the explosion extended along the notched di-rection,with cracks from the first borehole longer than those from the second.At 30 μs delay time,cracks between the boreholes showed a"hook-like"distribution at their convergence point,with a lar-ger deflection angle in the cracks from the rear borehole.Propagation velocities,dynamic stress intensi-ty factors and dynamic energy release rates exhibited consistent trends,showing significant increase when the cracks approached each other.Cracks from the first borehole displayed pronounced fluctua-tions.Both cracks transformed into I-II mixed mode and then propagated alternately.At 180 μs delay time,the directional control provided by the second borehole's notch was weakened horizontally and formed a"Y-shaped"crack distribution,significantly affecting crack propagation velocity of the first borehole.This study offers references for optimizing delay times and improving rock breaking efficiency.