Mechanisms of Asymmetric Dynamic Response Induced by Weak Interlayer Geometry and Wave Impedance in Single-Hole Bench Blasting

Weak interlayers in layered rock masses can strongly influence stress-wave propagation, crack development, block motion, and flyrock behavior during bench slope blasting. To clarify the controlling mechanisms, a quasi-two-dimensional single-hole bench-slope model containing a weak interlayer was established using a continuous-discontinuous element method. Three single-factor groups were designed to examine the effects of interlayer thickness, dip angle, and wave impedance on the dynamic response of the slope. The results show that the weak interlayer acts as a geometric and dynamic symmetry-breaking interface. Relative to the locally quasi-radial response around the centrally initiated charge, interface reflection, transmission, and local dissipation produce direction-dependent stress, velocity, crack, and displacement fields. Interlayer thickness controls the spatial extent of this asymmetric response, dip angle determines its preferred direction, and wave impedance governs its dynamic intensity through unequal energy partition across the interface. Within the respective single-factor analyses, relatively larger flyrock responses were observed for the cases with a 2.0 m interlayer thickness, a 70° dip angle, and a low-wave-impedance interlayer. These observations represent comparative trends within the present quasi-two-dimensional single-hole model and should not be regarded as direct predictions of field-scale flyrock risk or a verified combined unfavorable blasting condition. These findings indicate that weak-interlayer geometry and mechanical contrast play important roles in controlling asymmetric blasting responses. Within the assumptions of the present quasi-two-dimensional single-hole model, the results provide mechanistic insights into relative response trends rather than direct field-scale blasting predictions.