Abstract
The effect of high delay time accuracy of electronic delay detonators (EDDs) on overbreak, remaining rock damage, and surface smoothness which are expected on smooth blasting was investigated by experimental and theoretical approach in comparison with that of pyrotechnically delayed detonators (PDDs).
As an experimental approach, test-blasts were conducted in a deep iron mine. The test site region, those composed of very hard granodiorite. Five rounds were performed, EDDs were used in the holes on the perimeter of the right half, and PDDs were used on the perimeter of the left half. Following each shot, the cross section was measured by laser to determine amount of overbreak and surface smoothness. In situ seismic prospecting was used to estimate the depth of damage in the remaining rock, and the damage was further investigated by boring into both side walls. Perimeter charge initiation by the EDDs resulted in better smooth blasting results than the PDDs.
As a theoretical approach, numerical simulation was adopted. This numerical simulation method is based upon a finite element method and rock fracture mechanics. The dynamic stress field induced by explosives is determined by a finite element scheme, and initiation and propagation of cracks are represented by the remeshing procedure. Furthermore, heterogeneity of rock strength and nonlinear mechanical behavior of cracks are also taken into account. Smooth blasting by complete simultaneous initiation (with no error initiation), simultaneous initiations with initiation error of an electronic delay detonator and with initiation error of a pyrotechnically delayed detonator was analyzed. The result from this numerical analysis supported the validity of the EDDs results on smooth blasting.